Kirstin Krüger

Publications

Peer-reviewed publications:

• Vettoretti, Guido; Hu, Ruei-Jia; Bethke, Ingo; Krüger, Kirstin; Sigl, Michael & Outten, Stephen et al, Volcanism-induced collapse and recovery of the Atlantic meridional overturning circulation under glacial conditions. Science Advances. 12(6). doi: 10.1126/sciadv.adx2124, 2026
• Wang, X., L. Coy, M. Fujiwara, P. Lin, A. Ming, F. Li, E. M. Bednarz, Z. Zhuo, K. Krüger, Chapter 4: Hunga effects on stratospheric temperatures and circulation. In APARC, 2025: The Hunga Eruption Atmospheric Impacts Report [Yunqian Zhu, Graham Mann, Paul A. Newman, William Randel (Eds.)]. APARC Report No. 11, WCRP Report No. 10/2025, DOI: 10.34734/FZJ-2025-05241, 2025. (https://aparc-climate.org/publications/aparc-report-no-11/)
• Collet Dominik, Sam White, Scott Bremer, Brita Brenna, Håkon Glørstad, Ingar Mørkestøl Gundersen, Heli Huhtamaa, Kirstin Krüger, Hans W. Linderholm, Fredrik Charpentier Ljungqvist et al, The Little Ice Age: The History and Future of a Traveling Concept, WIREs Climate Change, https://doi.org/10.1002/wcc.70023, 2025.
• Zoëga, T, T Storelvmo, K Krüger, Climate state dependent response to very large Icelandic effusive volcanic eruptions, Geophysical Research Letters 52 (16), e2025GL114638, 2025.
• Zoëga, T, T Storelvmo, K Krüger, Arctic warming from a high-latitude effusive volcanic eruption, Scientific Reports 15 (1), 14653, 2025.
• Ballo, EG, WJ D'Andrea, HI Høeg, K Loftsgarden, M Bajard, S Eckhardt, Massimo Cassiani, Nikolaos Evangeliou, Jostein Bakke, Kirstin Krüger, 2000 years of climate, environmental, and societal variability in southeastern Norway from the annually laminated sediments of Lake Sagtjernet, Quaternary Science Reviews 354, 109232, 2025.
• Zoëga, T, T Storelvmo, K Krüger, Modelled surface climate response to effusive Icelandic volcanic eruptions: sensitivity to season and size, Atmospheric Chemistry and Physics 25 (5), 2989-3010, 2025.
• Fuglestvedt, HF, I Gabriel, M Sigl, T Thordarson, K Krüger, Revisiting the 10th‐century Eldgjá eruption: Modeling the climatic and environmental impacts, Geophysical Research Letters 52 (1), e2024GL110507, 2025.
• Zhuo, Z, HF Fuglestvedt, M Toohey, K Krüger, Initial atmospheric conditions control transport of volcanic volatiles, forcing and impacts, Atmospheric Chemistry and Physics 24 (10), 6233-6249, 2024.
• van Dijk, EJC, J Jungclaus, M Sigl, C Timmreck, K Krüger, High-frequency climate forcing causes prolonged cold periods in the Holocene, Communications Earth & Environment 5 (1), 242, 2024.
• Fuglestvedt, HF, Z Zhuo, M Toohey, K Krüger, Volcanic forcing of high-latitude Northern Hemisphere eruptions, Npj Climate and Atmospheric Science 7 (1), 10, 2024.
• van Dijk, Evelien; Gundersen, Ingar Mørkestøl; Bode, Anna de; Høeg, Helge Irgens; Loftsgarden, Kjetil & Iversen, Frode, Claudia Timmreck, Johann Jungclaus, and Kirstin Krüger, Climate and societal impacts in Scandinavia following the 536 and 540 CE volcanic double event. Climate of the Past, 19(2), p. 357–398. doi: 10.5194/cp-19-357-2023, 2023.
• van Dijk, E, J Jungclaus, S Lorenz, C Timmreck, K Krüger, Was there a volcanic-induced long-lasting cooling over the Northern Hemisphere in the mid-6th–7th century? Climate of the Past 18 (7), 1601-1623, 2022.
• Brenna, H., Kutterolf, S., & Krüger, K. (2019). Global ozone depletion and increase of UV radiation caused by pre-industrial tropical volcanic eruptions. Sci Rep 9, 9435, https://doi.org/10.1038/s41598-019-45630-0.
• Toohey, M., Krüger, K., Schmidt, H. et al. (2019). Disproportionately strong climate forcing from extratropical explosive volcanic eruptions. Nature Geosci 12, 100–107, https://doi.org/10.1038/s41561-018-0286-2
• Toohey, M., K. Krüger, M. Sigl, F. Stordal, & H. Svensen, H. (2016). Climatic and societal impacts of a volcanic double event at the dawn of the Middle Ages, Climatic Change, 136, 401–412, https://doi.org/10.1007/s10584-016-1648-7
• Krüger, K., Kutterolf, S., T.H., Hansteen, (2015). Chapter 16: Halogen release from Plinian eruptions and depletion of stratospheric Ozone, Volcanism and global environmental change, Cambridge University Press, ISBN: 9781107058378, Ed. A. Schmidt et al., PP. 244-259.
• Sigl, M., J.R. McConnell, M. Toohey, M. Curran, S.B. Das, R. Edwards, E. Isaksson, K. Kawamura, S. Kipfstuhl, K. Krüger, L. Layman, O. Maselli, Y. Motizuki, H. Motoyama, D. Pasteris, & M. Severi, (2014)  Insights from Antarctica on volcanic forcing during the Common Era. Nature Clim Change 4, 693–697, https://doi.org/10.1038/nclimate2293
• Montzka, S., S. Reimann, S. O'Doherty, A. Engel, K. Krüger & W.T., Sturges, (2011). Chapter 1: Ozone-Depleting Substances and Related Chemicals, Scientific Assessment of Ozone Depletion: 2010, PP 112.
• Butchart, N, A. Charlton-Perez, I., Cionni, S.C., Hardiman, Krüger, K. et al. (2010). Chapter 4: Stratospheric Dynamics, SPARC CCMVal Report on the Evaluation of Chemistry-Climate Models, SPARC No. 5, WCRP-132, WMO/TD-No. 1526, PP 109-148.

• Weber, Lisa; Krüger, Kirstin & Fiedler, Stephanie (2026). On CMIP6 Model Consensus for the Climate Response in Eurasian Winter to Historical Volcanic Eruptions. Geophysical Research Letters. ISSN 0094-8276. 53(7). doi: 10.1029/2025GL120522. Full text in Research Archive Show summary

  This study provides a comprehensive analysis of the climate response in Northern Hemisphere (NH) winter to major volcanic eruptions of the past, using multi-member ensembles of historical experiments of 15 models from the Coupled Model Intercomparison Project Phase 6 (CMIP6) and three reanalysis data sets. Focusing on the two largest historical eruptions of Krakatoa and Pinatubo, the results highlight a large model consensus on the strengthening of the polar vortex and an associated increase in surface temperatures over parts of Northern Eurasia in the CMIP6 multi-model mean in the first winter following the eruptions. This finding is consistent with models simulating a positive phase of the North Atlantic Oscillation (NAO). The responses of the surface temperatures and winds show hardly any dependence on the phase of the El Niño-Southern Oscillation (ENSO).

• Vettoretti, Guido; Hu, Ruei-Jia; Bethke, Ingo; Krüger, Kirstin; Sigl, Michael & Outten, Stephen [Show all 11 contributors for this article] (2026). Volcanism-induced collapse and recovery of the Atlantic meridional overturning circulation under glacial conditions. Science Advances. 12(6). doi: 10.1126/sciadv.adx2124. Full text in Research Archive Show summary

  Volcanic eruptions have considerable impacts on climate across various timescales; however, it remains uncertain if, and how, volcanic activity could drive climate change over multiple millennia. Here we incorporate realistic volcanic forcing into a large ensemble of glacial era–coupled atmosphere-ocean model simulations. These simulations are constrained by sulfate records from ice cores, which help estimate the timing of past major eruptions. We investigate how volcanic eruptions may have occasionally triggered abrupt climate change during the last glacial period. Our results show that very large equatorial eruptions can induce large changes in the Atlantic Meridional Overturning Circulation via atmospheric and ocean circulation changes and air-sea buoyancy fluxes, potentially pushing the climate system between persistent warm and cold states lasting millennia. A simplified perspective of the dynamics shows how unforced natural climate variability may exert a stabilizing influence decades after an eruption, especially as the system nears a tipping point.

• Zoëga, Tómas; Storelvmo, Trude & Krüger, Kirstin (2025). Climate State Dependent Response to Very Large Icelandic Effusive Volcanic Eruptions. Geophysical Research Letters. ISSN 0094-8276. 52(16). doi: 10.1029/2025gl114638. Full text in Research Archive Show summary

  Effusive volcanic eruptions have been common in Iceland throughout the Holocene with the largest ones happening prior to the industrial revolution. Such eruptions can affect climate through the formation of sulfate aerosols and subsequent impacts on clouds. As different atmospheric conditions modulate the cloud and climate responses to aerosol perturbations, a pre‐industrial effusive eruption might have different climate impacts were it to happen today or in the future. Here we use an Earth system model to simulate the surface climate response to Icelandic effusive volcanic eruptions under pre‐industrial, present day, and end of the 21st century climate conditions. For the last case, high anthropogenic greenhouse gas and aerosol emissions are assumed. We find that the climate state significantly modulates the climate response, especially in the Arctic where we model amplified surface warming during winter under pre‐industrial conditions and stronger surface cooling during summer in warmer climates.

• Collet, Dominik; White, Sam; Bremer, Scott; Brenna, Brita; Glørstad, Håkon & Gundersen, Ingar Mørkestøl [Show all 13 contributors for this article] (2025). The Little Ice Age: The History and Future of a Traveling Concept. Wiley Interdisciplinary Reviews: Climate Change (WIRESs). ISSN 1757-7780. 16(5). doi: 10.1002/wcc.70023. Full text in Research Archive Show summary

  First coined in the 1930s, with reference to glaciation in North America, the concept of the “Little Ice Age” has undergone continuous revisions. It has traveled academically from glaciology to climatology, archeology, history, and, most recently, climate communication. Over time, it has grown into one of the most discussed topics in the field of climate history and attracts both considerable scholarly interest and public attention. The term “Little Ice Age” has been criticized for oversimplifying climatic change, focusing too much on temperature, and excluding possible effects on humans. Yet it remains a powerful “boundary object” in interdisciplinary cooperation, science communication, and the “environing” of history. In this sense, it serves similar functions as other concepts in the field of human–environment interactions, such as “global warming” or “climate resilience.” This article investigates the contested history and the potential uses of the “Little Ice Age” concept. It explores how the concept encourages interdisciplinary consilience, global perspectives, and public debate. In summary, these aspects are connected and contrasted to the use of similar concepts, such as “climate resilience” and “tipping points” in the sphere of climate–society interactions. This article is categorized under: Climate, History, Society, Culture > Major Historical Eras Perceptions, Behavior, and Communication of Climate Change > Communication Vulnerability and Adaptation to Climate Change > Learning from Cases and Analogies

• Ballo, Eirik Gottschalk; D’Andrea, William J.; Høeg, Helge Irgens; Loftsgarden, Kjetil; Bajard, Manon Juliette Andree & Eckhardt, Sabine [Show all 10 contributors for this article] (2025). 2000 years of climate, environmental, and societal variability in southeastern Norway from the annually laminated sediments of Lake Sagtjernet. Quaternary Science Reviews. ISSN 0277-3791. 354. doi: 10.1016/j.quascirev.2025.109232. Full text in Research Archive Show summary

  Previous Common Era (i.e., the past 2000 years) climate reconstructions from Fennoscandia have focused on northern and central areas, with scarce data from the southern areas. Using varved sediments from Lake Sagtjernet in southeastern Norway, we developed a hydrogen isotope record from sedimentary leaf waxes (n-alkanes) as a proxy for hydrogen isotopes in precipitation, which we interpret as an indicator of temperature variability over the past 2000 years. The climate reconstruction provides high, decadal resolution for the period 360–770 CE, allowing critical evaluation during the Dark Ages Cold Period (around 300–800 CE) and a cooling during the 6th century, previously suggested as the coldest period of the Common Era. Our results reveal that the most rapid drop in temperature occurred from 536 to 545 CE (+74/-90 years), corresponding in time to the 536 and 540 CE volcanic eruptions. We also document an inferred cold interval that persisted from around 650 to 710 CE (+72/-90 years). While past studies have suggested prolonged cooling during the Dark Ages Cold Period, our findings show that, on average, the climate during 360–770 CE was similar to the Common Era average in the Lake Sagtjernet record. To explore socio-environmental interactions throughout the past 2000 years, we present a pollen-based environmental reconstruction and integrate it with archaeological evidence from around Lake Sagtjernet. These analyses reveal significant societal activities such as land clearing, cereal cultivation, and large-scale iron production, which drastically altered the landscape in the Viking Age (around 800–1050 CE) and the first half of the Norwegian Middle Ages (around 1050–1350 CE). Modern cultivation practices following the Black Death (1349–1350 CE) were first established around 1470 CE and increased continuously until around 1940 CE. Intensification of societal activities through the past millennium, including iron production and modern cultivation, occurred during both warmer (Medieval Climate Anomaly; 950–1250 CE) and colder (Little Ice Age; 1450–1850 CE) periods.

• Zoega, Tomas; Storelvmo, Trude & Krüger, Kirstin (2025). Modelled surface climate response to effusive Icelandic volcanic eruptions: sensitivity to season and size. Atmospheric Chemistry and Physics (ACP). ISSN 1680-7316. 25(5), p. 2989–3010. doi: 10.5194/acp-25-2989-2025. Full text in Research Archive Show summary

  Effusive, long-lasting volcanic eruptions impact climate through the emission of gases and the subsequent production of aerosols. Previous studies, both modelling and observational, have made efforts to quantify these impacts and untangle them from natural variability. However, due to the scarcity of large and well-observed effusive volcanic eruptions, our understanding remains patchy. Here, we use an Earth system model to systematically investigate the climate response to high-latitude, effusive volcanic eruptions, similar to the 2014–2015 Holuhraun eruption in Iceland, as a function of eruption season and size. The results show that the climate response is regional and strongly modulated by different seasons, exhibiting midlatitude cooling during summer and Arctic warming during winter. Furthermore, as eruptions increase in size in terms of sulfur dioxide emissions, the climate response becomes increasingly insensitive to variations in emission strength, levelling off for eruptions between 20 and 30 times the size of the 2014–2015 Holuhraun eruption. Volcanic eruptions are generally considered to lead to surface cooling, but our results indicate that this is an oversimplification, especially in the Arctic, where warming is found to be the dominant response during autumn and winter.

• Zoega, Tomas; Storelvmo, Trude & Krüger, Kirstin (2025). Arctic warming from a high-latitude effusive volcanic eruption. Scientific Reports. 15(1). doi: 10.1038/s41598-025-98811-5. Full text in Research Archive Show summary

  The effusive Holuhraun eruption in Iceland emitted large quantities of sulfur into the troposphere during the fall and winter of 2014–15. Previous studies have shown that the resulting volcanic aerosols led to reduced insolation, and thus surface cooling, through increased cloud shortwave reflectance, mostly over the North Atlantic and Europe. Less attention has been paid to the Arctic, which at the time of the eruption received limited sunlight. Based on evidence from observations and model simulations, here we argue that increased cloud liquid water path and cloud cover following the 2014–15 Holuhraun eruption led to surface warming in the Arctic through trapping of longwave radiation. Our results show that sulfur emissions from the eruption led to extended lifetime of low and middle level clouds, reducing the longwave radiative cooling of the surface. This is the first time, to our knowledge, that an effusive volcanic eruption is shown to have this effect. Given the high level of volcanic activity in Iceland, these findings demonstrate the need to further investigate the climate impacts of high-latitude effusive volcanic eruptions. Moreover, marine cloud brightening through cloud seeding has been suggested as one way to combat anthropogenic climate change but, as our results suggest, such actions might have counteractive regional consequences.

• Fuglestvedt, Herman Fæhn; Gabriel, Imogen; Sigl, Michael; Thordarson, Thorvaldur & Krüger, Kirstin (2025). Revisiting the 10th-Century Eldgjá Eruption: Modeling the Climatic and Environmental Impacts. Geophysical Research Letters. ISSN 0094-8276. 52(1). doi: 10.1029/2024GL110507. Full text in Research Archive Show summary

  The 10th-century Eldgjá eruption in Iceland is the largest basaltic flood lava eruption of the Common Era. However, the extent of its impacts is unclear due to limited historical records. Combining volcanology and ice-core analyses from both recent and earlier studies, we present a gas emissions scenario for the Eldgjá eruption spanning 937 to 940 CE, co-injecting volcanic sulfur and halogens. The combined tropospheric and stratospheric sulfur emissions are 3–8 times higher than those adopted for Eldgjá in existing paleoclimate simulations. Earth system modeling of this scenario under pre-industrial conditions reveals a compound event with maximum northern extratropics surface cooling of ∼2°C in summer-autumn of 939 and 940 CE, prolonged Arctic sea ice growth, and large-scale precipitation changes, concurrent with stratospheric ozone depletion and elevated pollution. These results imply that the combined climatic and environmental effects of the Eldgjá eruption may have significantly impacted human populations at the time.

• Dijk, Evelien Van; Jungclaus, Johann; Sigl, Michael; Timmreck, Claudia & Krüger, Kirstin (2024). High-frequency climate forcing causes prolonged cold periods in the Holocene. Communications Earth & Environment. 5. doi: 10.1038/s43247-024-01380-0. Full text in Research Archive Show summary

  Understanding climate variability across interannual to centennial timescales is critical, as it encompasses the natural range of climate fluctuations that early human agricultural societies had to adapt to. Deviations from the long-term mean climate are often associated with both societal collapse and periods of prosperity and expansion. Here, we show that contrary to what global paleoproxy reconstructions suggest, the mid to late-Holocene was not a period of climate stability. We use mid- to late-Holocene Earth System Model simulations, forced by state-of-the-art reconstructions of external climate forcing to show that eleven long-lasting cold periods occurred in the Northern Hemisphere during the past 8000 years. These periods correlate with enhanced volcanic activity, where the clustering of volcanic eruptions induced a prolonged cooling effect through gradual ocean-sea ice feedback. These findings challenge the prevailing notion of the Holocene as a period characterized by climate stability, as portrayed in multi-proxy climate reconstructions. Instead, our simulations provide an improved representation of amplitude and timing of temperature variations on sub-centennial timescales.

• Zhuo, Zhihong; Fuglestvedt, Herman Fæhn; Toohey, Matthew & Krüger, Kirstin (2024). Initial atmospheric conditions control transport of volcanic volatiles, forcing and impacts. Atmospheric Chemistry and Physics (ACP). ISSN 1680-7316. 24(10), p. 6233–6249. doi: 10.5194/acp-24-6233-2024. Full text in Research Archive Show summary

  Volcanic eruptions impact the climate and environment. The volcanic forcing is determined by eruption source parameters, including the mass and composition of volcanic volatiles, eruption season, eruption latitude, and injection altitude. Moreover, initial atmospheric conditions of the climate system play an important role in shaping the volcanic forcing and response. However, our understanding of the combination of these factors, the distinctions between tropical and extratropical volcanic eruptions, and the co-injection of sulfur and halogens remains limited. Here, we perform ensemble simulations of volcanic eruptions at 15 and 64° N in January, injecting 17 Mt of SO2 together with HCl and HBr at 24 km altitude. Our findings reveal that initial atmospheric conditions control the transport of volcanic volatiles from the first month and modulate the subsequent latitudinal distribution of sulfate aerosols and halogens. This results in different volcanic forcing, surface temperature and ozone responses over the globe and Northern Hemisphere extratropics (NHET) among the model ensemble members with different initial atmospheric conditions. NH extratropical eruptions exhibit a larger NHET mean volcanic forcing, surface cooling and ozone depletion compared with tropical eruptions. However, tropical eruptions lead to more prolonged impacts compared with NH extratropical eruptions, both globally and in the NHET. The sensitivity of volcanic forcing to varying eruption source parameters and model dependency is discussed, emphasizing the need for future multi-model studies to consider the influence of initial conditions and eruption source parameters on volcanic forcing and subsequent impacts.

• Booge, Dennis; Tjiputra, Jerry; Oliviè, Dirk Jan Leo; Quack, Birgit & Krüger, Kirstin (2024). Natural marine bromoform emissions in the fully coupled ocean-atmosphere model NorESM2. Earth System Dynamics (ESD). ISSN 2190-4979. 15(3), p. 801–816. doi: 10.5194/esd-15-801-2024. Full text in Research Archive Show summary

  Oceanic bromoform (CHBr3) is an important precursor of atmospheric bromine. Although highly relevant for the future halogen burden and ozone layer in the stratosphere, global CHBr3 production in the ocean and its emissions are still poorly constrained in observations and are mostly neglected in climate models. Here, we newly implement marine CHBr3 in the second version of the state-of-the-art Norwegian Earth System Model (NorESM2) with fully coupled interactions of ocean, sea ice, and atmosphere. Our results are validated using oceanic and atmospheric observations from the HalOcAt (Halocarbons in the Ocean and Atmosphere) database. The simulated mean oceanic concentrations (6.61 ± 3.43 pmol L−1) are in good agreement with observations from open-ocean regions (5.02 ± 4.50 pmol L−1), while the mean atmospheric mixing ratios (0.76 ± 0.39 ppt) are lower than observed but within the range of uncertainty (1.45 ± 1.11 ppt). The NorESM2 ocean emissions of CHBr3 (214 Gg yr−1) are within the range of or higher than previously published estimates from bottom-up approaches but lower than estimates from top-down approaches. Annual mean fluxes are mostly positive (sea-to-air fluxes); driven by oceanic concentrations, sea surface temperature, and wind speed; and dependent on season and location. During winter, model results imply that some oceanic regions in high latitudes act as sinks of atmospheric CHBr3 due to their elevated atmospheric mixing ratios. We further demonstrate that key drivers for oceanic and atmospheric CHBr3 variability are spatially heterogeneous. In the tropical West Pacific, which is a hot spot for oceanic bromine delivery to the stratosphere, wind speed is the main driver for CHBr3 fluxes on an annual basis. In the North Atlantic, as well as in the Southern Ocean region, atmospheric and oceanic CHBr3 variabilities interact during most of the seasons except for the winter months, when sea surface temperature is the main driver. Our study provides an improved process-based understanding of the biogeochemical cycling of CHBr3 and more reliable natural emission estimates, especially on seasonal and spatial scales, compared to previously published model estimates.

• Fuglestvedt, Herman Fæhn; Zhuo, Zhihong; Toohey, Matthew & Krüger, Kirstin (2024). Volcanic forcing of high-latitude Northern Hemisphere eruptions. npj Climate and Atmospheric Science. 7(1), p. 1–12. doi: 10.1038/s41612-023-00539-4. Full text in Research Archive Show summary

  High-latitude explosive volcanic eruptions can cause substantial hemispheric cooling. Here, we use a whole-atmosphere chemistry- climate model to simulate Northern Hemisphere (NH) high-latitude volcanic eruptions of magnitude similar to the 1991 Mt. Pinatubo eruption. Our simulations reveal that the initial stability of the polar vortex strongly influences sulphur dioxide lifetime and aerosol growth by controlling the dispersion of injected gases after such eruptions in winter. Consequently, atmospheric variability introduces a spread in the cumulative aerosol radiative forcing of more than 20%. We test the aerosol evolution’s sensitivity to co- injection of sulphur and halogens, injection season, and altitude, and show how aerosol processes impact radiative forcing. Several of these sensitivities are of similar magnitude to the variability stemming from initial conditions, highlighting the significant influence of atmospheric variability. We compare the modelled volcanic sulphate deposition over the Greenland i

• Hutchison, William; Gabriel, Imogen; Plunkett, Gill; Burke, Andrea; Sugden, Patrick & Innes, Helen [Show all 17 contributors for this article] (2024). High-Resolution Ice-Core Analyses Identify the Eldgjá Eruption and a Cluster of Icelandic and Trans-Continental Tephras Between 936 and 943 CE. Journal of Geophysical Research (JGR): Atmospheres. ISSN 2169-897X. 129(16). doi: 10.1029/2023JD040142. Full text in Research Archive Show summary

  The Eldgjá eruption is the largest basalt lava flood of the Common Era. It has been linked to a major ice-core sulfur (S) spike in 939–940 CE and Northern Hemisphere summer cooling in 940 CE. Despite its magnitude and potential climate impacts, uncertainties remain concerning the eruption timeline, atmospheric dispersal of emitted volatiles, and coincident volcanism in Iceland and elsewhere. Here, we present a comprehensive analysis of Greenland ice-cores from 936 to 943 CE, revealing a complex volatile record and cryptotephra with numerous geochemical populations. Transitional alkali basalt tephra matching Eldgjá are found in 939–940 CE, while tholeiitic basalt shards present in 936/937 CE and 940/941 CE are compatible with contemporaneous Icelandic eruptions from Grímsvötn and Bárðarbunga-Veiðivötn systems (including V-Sv tephra). We also find four silicic tephra populations, one of which we link to the Jala Pumice of Ceboruco (Mexico) at 941 ± 1 CE. Triple S isotopes, Δ33S, spanning 936–940 CE are indicative of upper tropospheric/lower stratospheric transport of aerosol sourced from the Icelandic fissure eruptions. However, anomalous Δ33S (down to −0.4‰) in 940–941 CE evidence stratospheric aerosol transport consistent with summer surface cooling revealed by tree-ring reconstructions. Tephra associated with the anomalous Δ33S have a variety of compositions, complicating the attribution of climate cooling to Eldgjá alone. Nevertheless, our study confirms a major S emission from Eldgjá in 939–940 CE and implicates Eldgjá and a cluster of eruptions as triggers of summer cooling, severe winters, and privations in ∼940 CE.

• Zhuo, Zhihong; Fuglestvedt, Herman Fæhn; Toohey, Matthey & Krüger, Kirstin (2023). Initial conditions control transport of volcanic volatiles, forcing and impacts. Atmospheric Chemistry and Physics Discussions (ACPD). doi: 10.5194/egusphere-2023-2374. Full text in Research Archive
• Dijk, Evelien Van; Gundersen, Ingar Mørkestøl; Bode, Anna de; Høeg, Helge Irgens; Loftsgarden, Kjetil & Iversen, Frode [Show all 9 contributors for this article] (2023). Climate and societal impacts in Scandinavia following the 536 and 540 CE volcanic double event. Climate of the Past. ISSN 1814-9324. 19(2), p. 357–398. doi: 10.5194/cp-19-357-2023. Full text in Research Archive Show summary

  In the Northern Hemisphere, the mid-6th century was one of the coldest periods of the last 2000 years, as indicated by both proxy records and Earth System Model (ESM) simulations. This cold period was initiated by volcanic eruptions in 536 CE and 540 CE. Evidence from historical sources, archaeological findings, and proxy records suggests that the extent and severity of this volcanic induced cooling was spatially heterogeneous and that the effect on society resulted in adaptation and resilience at some locations, whereas social crisis has been indicated at others. Here, we study the effect of the volcanic double event in 536 CE and 540 CE on the climate and society in Scandinavia with a special focus on Southern Norway. Using an ensemble of Max Planck Institute ESM transient simulations for 521–680 CE, the temperature, precipitation and atmospheric circulation patterns are studied. The simulated cooling magnitude is then used as input for the growing degree day (GDD) model set-up for Southern Norway. This GDD model indicates the possible effects on agriculture for three different study areas in Southern Norway, representative of typical meteorological and landscape conditions. Pollen from bogs and archaeological records inside the study area are then analysed at high resolution (1–3 cm sample intervals) to give insights into the validity of the GDD model set-up with regard to the volcanic climate impact on the regional scale, and to link the different types of data sets. After the 536/540 CE double event, a maximum surface air cooling of up to 3.5 °C during the mean growing season is simulated regionally in Southern Norway. With a worst-case scenario cooling of 3 °C, the GDD model indicates crop failures were likely in our northernmost and western study areas, while crops were more likely to mature in the southeastern study area. These results are in agreement with the pollen records from the respective areas. During the sixth century, excavations show an abandonment of farms, severe social impact but also a continuation of occupation or a mix of those. In addition, archaeological findings from one of the excavation sites suggest wetter conditions for the mid-sixth century in Scandinavia, as simulated by individual ensemble members. Finally, we discuss the likely climate and societal impacts of the 536/540 CE volcanic double event by synthesising the new and available data sets for the whole Scandinavia.

• Ridderseth, Hilde; Daltveit, Dagrun Slettebø; Hollund, Bjørg Eli; Kirkeleit, Jorunn; Kromhout, Hans & Krüger, Kirstin [Show all 8 contributors for this article] (2023). Validation of a full-shift benzene exposure empirical model developed for work on offshore petroleum installations on the Norwegian continental shelf. Journal of Occupational and Environmental Hygiene. ISSN 1545-9624. 20(10). doi: 10.1080/15459624.2023.2242416. Full text in Research Archive Show summary

  Workers on offshore petroleum installations might be exposed to benzene, a carcinogenic agent. Recently, a full-shift benzene exposure model was developed based on personal measurements. This study aimed to validate this exposure model by using datasets not included in the model. The exposure model was validated against an internal dataset of measurements from offshore installations owned by the same company that provided data for the model, and an external dataset from installations owned by another company. We used Tobit regression to estimate GM (geometric mean) benzene exposure overall and for individual job groups. Bias, relative bias, precision, and correlation were estimated to evaluate the agreement between measured exposures and the levels predicted by the model. Overall, the model overestimated exposure when compared to the predicted exposure level to the internal dataset with a factor of 1.7, a relative bias of 73%, a precision of 0.6, a correlation coefficient of 0.72 (p = 0.019), while the Lin’s Concordance Correlation Coefficient (CCC) was 0.53. The model underestimated exposure when compared to the external dataset with a factor of about 2, with a relative bias of −45%, a precision of 1.2, a correlation coefficient of 0.31 (p = 0.544), and a Lin’s CCC of 0.25. The exposure model overestimated benzene exposure in the internal validation dataset, while the precision and the correlation between the measured and predicted exposure levels were high. Differences in measurement strategies could be one of the reasons for the discrepancy. The exposure model agreed less with the external dataset.

• Liu, Guangyu; Hirooka, Toshihiko; Eguchi, Nawo & Krüger, Kirstin (2022). Dynamical evolution of a minor sudden stratospheric warming in the Southern Hemisphere in 2019. Atmospheric Chemistry and Physics (ACP). ISSN 1680-7316. 22(5), p. 3493–3505. doi: 10.5194/acp-22-3493-2022. Full text in Research Archive Show summary

  A major strong sudden stratospheric warming (SSW) occurred in the Southern Hemisphere (SH) stratosphere in 2002 (hereafter referred to as SSW2002), which is one of the most unusual winters in the SH. Following several warmings, the polar vortex broke down in midwinter. Eastward-traveling waves and their interaction with quasi-stationary planetary waves played an important role during this event. This study analyzed the Japanese 55-year reanalysis (JRA-55) dataset to examine the SSW event that occurred in the SH in 2019 (hereafter referred to as SSW2019). In 2019, a rapid temperature increase and decelerated westerly winds were observed at the polar cap, but since there was no reversal of westerly winds to easterly winds at 60∘ S in the middle to lower stratosphere, the SSW2019 was classified as a minor warming event. The results showed that quasi-stationary planetary waves of zonal wavenumber 1 developed during the SSW2019. The strong vertical component of the Eliassen–Palm flux with zonal wavenumber 1 is indicative of pronounced propagation of planetary waves to the stratosphere. The wave driving in September 2019 was larger than that of the major SSW event in 2002. Major SSWs tend to accompany preceding minor warmings, preconditioning, which changes the zonal flow that weaken the polar night jet as seen in SSW2002. A similar preconditioning was hardly observed in SSW2019. The strong wave driving in SSW2019 occurred in high latitudes. Waveguides (i.e., positive values of the refractive index squared) were found at high latitudes in the upper stratosphere during the warming period, which provided favorable conditions for quasi-stationary planetary waves to propagate upward and poleward.

• Fang, Shih-Wei; Timmreck, Claudia; Jungclaus, Johann; Krüger, Kirstin & Schmidt, Hauke (2022). On the additivity of climate responses to the volcanic and solar forcing in the early 19th century. Earth System Dynamics (ESD). ISSN 2190-4979. 13(4), p. 1535–1555. doi: 10.5194/esd-13-1535-2022. Full text in Research Archive Show summary

  The early 19th century was the coldest period over the past 500 years, when strong tropical volcanic events and a solar minimum coincided. The 1809 unidentified eruption and the 1815 Tambora eruption happened consecutively during the Dalton minimum of solar irradiance; however, the relative role of the two forcing (volcano and solar) agents is still unclear. In this study, we examine the responses from a set of early 19th century simulations with combined and separated volcanic and solar forcing agents, as suggested in the protocol for the past1000 experiment of the Paleoclimate Modelling Intercomparison Project – Phase 4 (PMIP4). From 20-member ensemble simulations with the Max Planck Institute Earth system model (MPI-ESM1.2-LR), we find that the volcano- and solar-induced surface cooling is additive in the global mean/large scale, regardless of combining or separating the forcing agents. The two solar reconstructions (SATIRE (Spectral and Total Irradiance REconstruction-Millennia model) and PMOD (Physikalisch-Meteorologisches Observatorium Davos)) contribute to a cooling before and after 1815 of ∼0.05 and ∼0.15 K monthly average near-surface air cooling, respectively, indicating a limited solar contribution to the early 19th century cold period. The volcanic events provide the main cooling contributions, inducing a surface cooling that peaks at ∼0.82 K for the 1809 event and ∼1.35 K for Tambora. After the Tambora eruption, the temperature in most regions increases toward climatology largely within 5 years, along with the reduction of volcanic forcing. In the northern extratropical oceans, the temperature increases slowly at a constant rate until 1830, which is related to the reduction of seasonality and the concurrent changes in Arctic sea-ice extent. The albedo feedback of Arctic sea ice is found to be the main contributor to the Arctic amplification of the cooling signal. Several non-additive responses to solar and volcanic forcing happen on regional scales. In the atmosphere, the stratospheric polar vortex tends to strengthen when combining both volcano and solar forcing, even though the two forcing agents separately induce opposite-sign changes in stratospheric temperatures and zonal winds. In the ocean, when combining the two forcings, additional surface cold water propagates to the northern extratropics from the additional solar cooling in the tropics, which results in regional cooling along the propagation. Overall, this study not only quantifies the surface responses from combinations of the volcano and solar forcing, but also highlights the components that cannot be simply added from the responses of the individual forcing agents, indicating that a relatively small forcing agent (such as solar in early 19th century) can impact the response from the large forcing (such as the 1815 Tambora eruption) when considering regional climates.

• Dijk, Evelien Van; Jungclaus, Johann; Lorenz, Stephan; Timmreck, Claudia & Krüger, Kirstin (2022). Was there a volcanic-induced long-lasting cooling over the Northern Hemisphere in the mid-6th-7th century? Climate of the Past. ISSN 1814-9324. 18(7), p. 1601–1623. doi: 10.5194/cp-18-1601-2022. Full text in Research Archive Show summary

  Abstract. The climate of the Northern Hemisphere (NH) in the mid-6th century was one of the coldest during the last 2 millennia based on multiple paleo-proxies. While the onset of this cold period can be clearly connected to the volcanic eruptions in 536 and 540 Common Era (CE), the duration, extent, and magnitude of the cold period are uncertain. Proxy data are sparse for the first millennium, which compounds the uncertainties of the reconstructions. To better understand the mechanisms of the prolonged cooling, we analyze new transient simulations over the Common Era and enhance the representation of mid-6th to 7th century climate by additional ensemble simulations covering 520–680 CE. We use the Max Planck Institute Earth System Model to apply the external forcing as recommended in the Paleoclimate Modelling Intercomparison Project phase 4. After the four large eruptions in 536, 540, 574, and 626 CE, a significant mean surface climate response in the NH lasting up to 20 years is simulated. The 2 m air temperature shows a cooling over the Arctic in winter, corresponding to the increase in Arctic sea ice, mainly in the Labrador Sea and to the east of Greenland. The increase in sea-ice extent relates to a decrease in the northward ocean heat transport into the Arctic within the first 2 years after the eruptions and to an increase in the Atlantic meridional overturning circulation, which peaks 10 years after the eruptions. A decrease in the global ocean heat content is simulated after the eruptions that does not recover during the simulation period. These ocean–sea-ice interactions sustain the surface cooling, as the cooling lasts longer than is expected solely from the direct effects of the volcanic forcing, and are thus responsible for the multi-decadal surface cooling. In boreal summer, the main cooling occurs over the continents at midlatitudes. A dipole pattern develops with high sea level pressure and a decrease in both precipitation and evaporation poleward of 40∘ N. In addition, more pronounced cooling over land compared to ocean leads to an enhanced land–sea contrast. While our model ensemble simulations show a similar ∼20-year summer cooling over NH land after the eruptions as tree ring reconstructions, a volcanic-induced century-long cooling, as reconstructed from tree ring data, does not occur in our simulations.

• Bajard, Manon Juliette Andree; Ballo, Eirik Gottschalk; Høeg, Helge Irgens; Bakke, Jostein; Støren, Eivind Wilhelm Nagel & Loftsgarden, Kjetil [Show all 11 contributors for this article] (2022). Climate adaptation of pre-Viking societies. Quaternary Science Reviews. ISSN 0277-3791. 278. doi: 10.1016/j.quascirev.2022.107374. Full text in Research Archive Show summary

  Understanding how the Viking societies were impacted by past climate variability and how they adapted to it has hardly been investigated. Here, we have carried out a new multi-proxy investigation of lake sediments, including geochemical and palynological analyses, to reconstruct past changes in temperature and agricultural practices of pre-Viking and Viking societies in Southeastern Norway during the period between 200 and 1300 CE. The periods 200–300 and 800–1300 CE were warmer than the 300–800 CE period, which is known as the “Dark Ages Cold Period”. This cold period was punctuated by century-scale more temperate intervals, which were dominated by the cultivation of cereals and hemp (before 280 CE, 420–480 CE, 580–700 CE, and after 800 CE). In between, cold intervals were dominated by livestock farming. Our results demonstrate that the pre-Viking societies changed their agricultural strategy in response to climate variability during the Late Antiquity.

• Hamer, Paul David; Marécal, Virginie; Hossaini, Ryan; Pirre, Michel; Krysztofiak, Gisele & Ziska, Franziska [Show all 19 contributors for this article] (2021). Cloud-scale modelling of the impact of deep convection on the fate of oceanic bromoform in the troposphere: a case study over the west coast of Borneo. Atmospheric Chemistry and Physics (ACP). ISSN 1680-7316. 21(22), p. 16955–16984. doi: 10.5194/acp-21-16955-2021. Full text in Research Archive Show summary

  This paper presents a modelling study on the fate of CHBr3 and its product gases in the troposphere within the context of tropical deep convection. A cloud-scale case study was conducted along the west coast of Borneo, where several deep convective systems were triggered on the afternoon and early evening of 19 November 2011. These systems were sampled by the Falcon aircraft during the field campaign of the SHIVA project and analysed using a simulation with the cloud-resolving meteorological model C-CATT-BRAMS at 2×2 km resolution that represents the emissions, transport by large-scale flow, convection, photochemistry, and washout of CHBr3 and its product gases (PGs). We find that simulated CHBr3 mixing ratios and the observed values in the boundary layer and the outflow of the convective systems agree. However, the model underestimates the background CHBr3 mixing ratios in the upper troposphere, which suggests a missing source at the regional scale. An analysis of the simulated chemical speciation of bromine within and around each simulated convective system during the mature convective stage reveals that >85 % of the bromine derived from CHBr3 and its PGs is transported vertically to the point of convective detrainment in the form of CHBr3 and that the remaining small fraction is in the form of organic PGs, principally insoluble brominated carbonyls produced from the photo-oxidation of CHBr3. The model simulates that within the boundary layer and free troposphere, the inorganic PGs are only present in soluble forms, i.e. HBr, HOBr, and BrONO2, and, consequently, within the convective clouds, the inorganic PGs are almost entirely removed by wet scavenging. We find that HBr is the most abundant PG in background lower-tropospheric air and that this prevalence of HBr is a result of the relatively low background tropospheric ozone levels at the regional scale. Contrary to a previous study in a different environment, for the conditions in the simulation, the insoluble Br2 species is hardly formed within the convective systems and therefore plays no significant role in the vertical transport of bromine. This likely results from the relatively small quantities of simulated inorganic bromine involved, the presence of HBr in large excess compared to HOBr and BrO, and the relatively efficient removal of soluble compounds within the convective column.

• Schure, Anneke Theresia Maria ter; Bajard, Manon Juliette Andree; Loftsgarden, Kjetil; Høeg, Helge Irgens; Ballo, Eirik Gottschalk & Bakke, Jostein [Show all 12 contributors for this article] (2021). Anthropogenic and environmental drivers of vegetation change in southeastern Norway during the Holocene. Quaternary Science Reviews. ISSN 0277-3791. 270. doi: 10.1016/j.quascirev.2021.107175. Full text in Research Archive Show summary

  Uncovering anthropogenic and environmental drivers behind past biological change requires integrated analyses of long-term records from a diversity of disciplines. We applied an interdisciplinary approach exploring effects of human land-use and environmental changes on vegetation dynamics at Lake Ljøgottjern in southeastern Norway during the Holocene. Combined analysis of pollen and sedimentary ancient DNA (sedaDNA) metabarcoding of the sedimentary sequence of the lake describes the vegetation dynamics at different scales, and establishes a timeline for pastoral farming activities. We integrate this reconstruction with geochemical analysis of the sediments, climate data, archaeological evidence of local human settlement and regional human population dynamics. Our data covering the last 10,000 years reveals consistent vegetation signals from pollen and sedaDNA indicating periods of deforestation connected to cultivation, matching the archaeological evidence. Multivariate analysis integrating the environmental data from geochemical and archaeological reconstructions with the vegetation composition indicates that the vegetation dynamics at Lake Ljøgottjern were primarily related to natural processes from the base of the core (in ca. 8000 BCE, Mesolithic) up to the Early Iron Age (ca. 500 BCE–550 CE), when agricultural activities in the region intensified. The pollen signal reflects the establishment of a Bronze Age (ca. 1800–500 BCE) farm in the area, while subsequent intensification of pollen concentrations of cultivated plants combined with the first sedaDNA signals of cultivation and pastoralism are consistent with evidence of the establishment of farming closer to the lake at around 300 BCE. These signals also correspond to the intensification of agriculture in southeastern Norway in the first centuries of the Early Iron Age. Applying an interdisciplinary approach allows us to reconstruct anthropogenic and environmental dynamics, and untangle effects of human land-use and environmental changes on vegetation dynamics in southeastern Norway during the Holocene.

• Brenna, Hans; Kutterolf, Steffen; Mills, Michael; Niemeier, Ulrike; Timmreck, Claudia & Krüger, Kirstin (2021). Decadal Disruption of the QBO by Tropical Volcanic Supereruptions. Geophysical Research Letters. ISSN 0094-8276. 48(5), p. 1–13. doi: 10.1029/2020GL089687. Full text in Research Archive Show summary

  The Los Chocoyos (14.6°N, 91.2°W) supereruption happened ∼75,000 years ago in Guatemala and was one of the largest eruptions of the past 100,000 years. It emitted enormous amounts of sulfur, chlorine, and bromine, with multi‐decadal consequences for the global climate and environment. Here, we simulate the impact of a Los Chocoyos‐like eruption on the quasi‐biennial oscillation (QBO), an oscillation of zonal winds in the tropical stratosphere, with a comprehensive aerosol chemistry Earth System Model. We find a ∼10‐year disruption of the QBO starting 4 months post eruption, with anomalous easterly winds lasting ∼5 years, followed by westerlies, before returning to QBO conditions with a slightly prolonged periodicity. Volcanic aerosol heating and ozone depletion cooling leads to the QBO disruption and anomalous wind regimes through radiative changes and wave‐mean flow interactions. Different model ensembles, volcanic forcing scenarios and results of a second model back up the robustness of our results.

• Tegtmeier, Susann; Atlas, Elliot; Quack, Birgit; Ziska, Franziska & Krüger, Kirstin (2020). Variability and past long-term changes of brominated very short-lived substances at the tropical tropopause. Atmospheric Chemistry and Physics (ACP). ISSN 1680-7316. 20, p. 7103–7123. doi: 10.5194/acp-20-7103-2020. Full text in Research Archive Show summary

  Abstract. Halogenated very short-lived substances (VSLSs), such as bromoform (CHBr3), can be transported to the stratosphere and contribute to the halogen loading and ozone depletion. Given their highly variable emission rates and their short atmospheric lifetimes, the exact amount as well as the spatio-temporal variability of their contribution to the stratospheric halogen loading are still uncertain. We combine observational data sets with Lagrangian atmospheric modelling in order to analyse the spatial and temporal variability of the CHBr3 injection into the stratosphere for the time period 1979–2013. Regional maxima with mixing ratios of up to 0.4–0.5 ppt at 17 km altitude are diagnosed to be over Central America (1) and over the Maritime Continent–west Pacific (2), both of which are confirmed by high-altitude aircraft campaigns. The CHBr3 maximum over Central America is caused by the co-occurrence of convectively driven short transport timescales and strong regional sources, which in conjunction drive the seasonality of CHBr3 injection. Model results at a daily resolution reveal isolated, exceptionally high CHBr3 values in this region which are confirmed by aircraft measurements during the ACCENT campaign and do not occur in spatially or temporally averaged model fields. CHBr3 injection over the west Pacific is centred south of the Equator due to strong oceanic sources underneath prescribed by the here-applied bottom-up emission inventory. The globally largest CHBr3 mixing ratios at the cold point level of up to 0.6 ppt are diagnosed to occur over the region of India, Bay of Bengal, and Arabian Sea (3); however, no data from aircraft campaigns are available to confirm this finding. Inter-annual variability of stratospheric CHBr3 injection of 10 %–20 % is to a large part driven by the variability of coupled ocean–atmosphere circulation systems. Long-term changes, on the other hand, correlate with the regional sea surface temperature trends resulting in positive trends of stratospheric CHBr3 injection over the west Pacific and Asian monsoon region and negative trends over the east Pacific. For the tropical mean, these opposite regional trends balance each other out, resulting in a relatively weak positive trend of 0.017±0.012 ppt Br per decade for 1979–2013, corresponding to 3 % Br per decade. The overall contribution of CHBr3 together with CH2Br2 to the stratospheric halogen loading accounts for 4.7 ppt Br, in good agreement with existing studies, with 50 % and 50 % being injected in the form of source and product gases, respectively.

• Wright, Jonathon S.; Sun, Xiaoyan; Konopka, Paul; Krüger, Kirstin; Legras, Bernard & Molod, Andrea [Show all 9 contributors for this article] (2020). Differences in tropical high clouds among reanalyses:origins and radiative impacts. Atmospheric Chemistry and Physics (ACP). ISSN 1680-7316. 20, p. 8989–9030. doi: 10.5194/acp-20-8989-2020. Full text in Research Archive Show summary

  Abstract. We examine differences among reanalysis high-cloud products in the tropics, assess the impacts of these differences on radiation budgets at the top of the atmosphere and within the tropical upper troposphere and lower stratosphere (UTLS), and discuss their possible origins in the context of the reanalysis models. We focus on the ERA5 (fifth-generation European Centre for Medium-range Weather Forecasts – ECMWF – reanalysis), ERA-Interim (ECMWF Interim Reanalysis), JRA-55 (Japanese 55-year Reanalysis), MERRA-2 (Modern-Era Retrospective Analysis for Research and Applications, Version 2), and CFSR/CFSv2 (Climate Forecast System Reanalysis/Climate Forecast System Version 2) reanalyses. As a general rule, JRA-55 produces the smallest tropical high-cloud fractions and cloud water contents among the reanalyses, while MERRA-2 produces the largest. Accordingly, long-wave cloud radiative effects are relatively weak in JRA-55 and relatively strong in MERRA-2. Only MERRA-2 and ERA5 among the reanalyses produce tropical-mean values of outgoing long-wave radiation (OLR) close to those observed, but ERA5 tends to underestimate cloud effects, while MERRA-2 tends to overestimate variability. ERA5 also produces distributions of long-wave, short-wave, and total cloud radiative effects at the top of the atmosphere that are very consistent with those observed. The other reanalyses all exhibit substantial biases in at least one of these metrics, although compensation between the long-wave and short-wave effects helps to constrain biases in the total cloud radiative effect for most reanalyses. The vertical distribution of cloud water content emerges as a key difference between ERA-Interim and other reanalyses. Whereas ERA-Interim shows a monotonic decrease of cloud water content with increasing height, the other reanalyses all produce distinct anvil layers. The latter is in better agreement with observations and yields very different profiles of radiative heating in the UTLS. For example, whereas the altitude of the level of zero net radiative heating tends to be lower in convective regions than in the rest of the tropics in ERA-Interim, the opposite is true for the other four reanalyses. Differences in cloud water content also help to explain systematic differences in radiative heating in the tropical lower stratosphere among the reanalyses. We discuss several ways in which aspects of the cloud and convection schemes impact the tropical environment. Discrepancies in the vertical profiles of temperature and specific humidity in convective regions are particularly noteworthy, as these variables are directly constrained by data assimilation, are widely used, and feed back to convective behaviour through their relationships with thermodynamic stability.

• Tegtmeier, Susann; Anstey, James; Davis, Sean; Dragani, Rossana; Harada, Yayoi & Ivanciu, Ioana [Show all 13 contributors for this article] (2020). Temperature and tropopause characteristics from reanalyses data in the tropical tropopause layer. Atmospheric Chemistry and Physics (ACP). ISSN 1680-7316. 20(2), p. 753–770. doi: 10.5194/acp-20-753-2020. Full text in Research Archive Show summary

  The tropical tropopause layer (TTL) is the transition region between the well-mixed convective troposphere and the radiatively controlled stratosphere with air masses showing chemical and dynamical properties of both regions. The representation of the TTL in meteorological reanalysis data sets is important for studying the complex interactions of circulation, convection, trace gases, clouds, and radiation. In this paper, we present the evaluation of climatological and long-term TTL temperature and tropopause characteristics in the reanalysis data sets ERA-Interim, ERA5, JRA-25, JRA-55, MERRA, MERRA-2, NCEP-NCAR (R1), and CFSR. The evaluation has been performed as part of the SPARC (Stratosphere–troposphere Processes and their Role in Climate) Reanalysis Intercomparison Project (S-RIP). The most recent atmospheric reanalysis data sets (ERA-Interim, ERA5, JRA-55, MERRA-2, and CFSR) all provide realistic representations of the major characteristics of the temperature structure within the TTL. There is good agreement between reanalysis estimates of tropical mean temperatures and radio occultation data, with relatively small cold biases for most data sets. Temperatures at the cold point and lapse rate tropopause levels, on the other hand, show warm biases in reanalyses when compared to observations. This tropopause-level warm bias is related to the vertical resolution of the reanalysis data, with the smallest bias found for data sets with the highest vertical resolution around the tropopause. Differences in the cold point temperature maximize over equatorial Africa, related to Kelvin wave activity and associated disturbances in TTL temperatures. Interannual variability in reanalysis temperatures is best constrained in the upper TTL, with larger differences at levels below the cold point. The reanalyses reproduce the temperature responses to major dynamical and radiative signals such as volcanic eruptions and the quasi-biennial oscillation (QBO). Long-term reanalysis trends in temperature in the upper TTL show good agreement with trends derived from adjusted radiosonde data sets indicating significant stratospheric cooling of around −0.5 to −1 K per decade. At 100 hPa and the cold point, most of the reanalyses suggest small but significant cooling trends of −0.3 to −0.6 K per decade that are statistically consistent with trends based on the adjusted radiosonde data sets. Advances of the reanalysis and observational systems over the last decades have led to a clear improvement in the TTL reanalysis products over time. Biases of the temperature profiles and differences in interannual variability clearly decreased in 2006, when densely sampled radio occultation data started being assimilated by the reanalyses. While there is an overall good agreement, different reanalyses offer different advantages in the TTL such as realistic profile and cold point temperature, continuous time series, or a realistic representation of signals of interannual variability. Their use in model simulations and in comparisons with climate model output should be tailored to their specific strengths and weaknesses.

• Brenna, Hans; Kutterolf, Steffen; Mills, Michael J. & Krüger, Kirstin (2020). The potential impacts of a sulfur- And halogen-rich supereruption such as Los Chocoyos on the atmosphere and climate. Atmospheric Chemistry and Physics (ACP). ISSN 1680-7316. 20(11), p. 6521–6539. doi: 10.5194/acp-20-6521-2020. Full text in Research Archive Show summary

  The supereruption of Los Chocoyos (14.6∘ N, 91.2∘ W) in Guatemala ∼84 kyr ago was one of the largest volcanic events of the past 100 000 years. Recent petrologic data show that the eruption released very large amounts of climate-relevant sulfur and ozone-destroying chlorine and bromine gases (523±94 Mt sulfur, 1200±156 Mt chlorine, and 2±0.46 Mt bromine). Using the Earth system model (ESM) of the Community Earth System Model version 2 (CESM2) coupled with the Whole Atmosphere Community Climate Model version 6 (WACCM6), we simulated the impacts of the sulfur- and halogen-rich Los Chocoyos eruption on the preindustrial Earth system. Our simulations show that elevated sulfate burden and aerosol optical depth (AOD) persists for 5 years in the model, while the volcanic halogens stay elevated for nearly 15 years. As a consequence, the eruption leads to a collapse of the ozone layer with global mean column ozone values dropping to 50 DU (80 % decrease) and leading to a 550 % increase in surface UV over the first 5 years, with potential impacts on the biosphere. The volcanic eruption shows an asymmetric-hemispheric response with enhanced aerosol, ozone, UV, and climate signals over the Northern Hemisphere. Surface climate is impacted globally due to peak AOD of >6, which leads to a maximum surface cooling of >6 K, precipitation and terrestrial net primary production decrease of >25 %, and sea ice area increases of 40 % in the first 3 years. Locally, a wetting (>100 %) and strong increase in net primary production (NPP) (>700 %) over northern Africa is simulated in the first 5 years and related to a southward shift of the Intertropical Convergence Zone (ITCZ) to the southern tropics. The ocean responds with pronounced El Niño conditions in the first 3 years that shift to the southern tropics and are coherent with the ITCZ change. Recovery to pre-eruption ozone levels and climate takes 15 years and 30 years, respectively. The long-lasting surface cooling is sustained by an immediate increase in the Arctic sea ice area, followed by a decrease in poleward ocean heat transport at 60∘ N which lasts up to 20 years. In contrast, when simulating Los Chocoyos conventionally by including sulfur and neglecting halogens, we simulate a larger sulfate burden and AOD, more pronounced surface climate changes, and an increase in column ozone. By comparing our aerosol chemistry ESM results to other supereruption simulations with aerosol climate models, we find a higher surface climate impact per injected sulfur amount than previous studies for our different sets of model experiments, since the CESM2(WACCM6) creates smaller aerosols with a longer lifetime, partly due to the interactive aerosol chemistry. As the model uncertainties for the climate response to supereruptions are very large, observational evidence from paleo archives and a coordinated model intercomparison would help to improve our understanding of the climate and environment response.

• Niemeier, Ulrike; Timmreck, Claudia & Krüger, Kirstin (2019). Revisiting the Agung 1963 volcanic forcing - Impact of one or two eruptions. Atmospheric Chemistry and Physics (ACP). ISSN 1680-7316. 19(15), p. 10379–10390. doi: 10.5194/acp-19-10379-2019. Full text in Research Archive Show summary

  In 1963 a series of eruptions of Mt. Agung, Indonesia, resulted in the third largest eruption of the 20th century and claimed about 1900 lives. Two eruptions of this series injected SO2 into the stratosphere, which can create a long-lasting stratospheric sulfate layer. The estimated mass flux of the first eruption was about twice as large as the mass flux of the second eruption. We followed the estimated emission profiles and assumed for the first eruption on 17 March an injection rate of 4.7 Tg SO2 and 2.3 Tg SO2 for the second eruption on 16 May. The injected sulfur forms a sulfate layer in the stratosphere. The evolution of sulfur is nonlinear and depends on the injection rate and aerosol background conditions. We performed ensembles of two model experiments, one with a single eruption and a second one with two eruptions. The two smaller eruptions result in a lower sulfur burden, smaller aerosol particles, and 0.1 to 0.3 Wm−2 (10 %–20 %) lower radiative forcing in monthly mean global average compared to the individual eruption experiment. The differences are the consequence of slightly stronger meridional transport due to different seasons of the eruptions, lower injection height of the second eruption, and the resulting different aerosol evolution. Overall, the evolution of the volcanic clouds is different in case of two eruptions than with a single eruption only. The differences between the two experiments are significant. We conclude that there is no justification to use one eruption only and both climatic eruptions should be taken into account in future emission datasets.

• Brenna, Hans; Kutterolf, Steffen & Krüger, Kirstin (2019). Global ozone depletion and increase of UV radiation caused by pre-industrial tropical volcanic eruptions. Scientific Reports. 9. doi: 10.1038/s41598-019-45630-0. Full text in Research Archive Show summary

  Large explosive tropical volcanic eruptions inject high amounts of gases into the stratosphere, where they disperse globally through the large-scale meridional circulation. There is now increasing observational evidence that volcanic halogens can reach the upper troposphere and lower stratosphere. Here, we present the first study that combines measurement-based data of sulfur, chlorine and bromine releases from tropical volcanic eruptions with complex coupled chemistry climate model simulations taking radiative-dynamical-chemical feedbacks into account. Halogen model input parameters represent a size-time-region-wide average for the Central American eruptions over the last 200 ka ensuring a comprehensive perspective. The simulations reveal global, long-lasting impact on the ozone layer affecting atmospheric composition and circulation for a decade. Column ozone drops below 220 DU (ozone hole conditions) in the tropics, Arctic and Antarctica, increasing biologically active UV by 80 to 400%. Our model results could potentially be validated using high-resolution proxies from ice cores and pollen records.

• Toohey, Matthew; Krüger, Kirstin; Schmidt, Hauke; Timmreck, Claudia; Sigl, Michael & Stoffel, Markus [Show all 7 contributors for this article] (2019). Disproportionately strong climate forcing from extratropical explosive volcanic eruptions. Nature Geoscience. ISSN 1752-0894. 12, p. 100–107. doi: 10.1038/s41561-018-0286-2. Full text in Research Archive Show summary

  Extratropical volcanic eruptions are commonly thought to be less effective at driving large-scale surface cooling than tropical eruptions. However, recent minor extratropical eruptions have produced a measurable climate impact, and proxy records suggest that the most extreme Northern Hemisphere cold period of the Common Era was initiated by an extratropical eruption in 536 ce. Using ice-core-derived volcanic stratospheric sulfur injections and Northern Hemisphere summer temperature reconstructions from tree rings, we show here that in proportion to their estimated stratospheric sulfur injection, extratropical explosive eruptions since 750 ce have produced stronger hemispheric cooling than tropical eruptions. Stratospheric aerosol simulations demonstrate that for eruptions with a sulfur injection magnitude and height equal to that of the 1991 Mount Pinatubo eruption, extratropical eruptions produce time-integrated radiative forcing anomalies over the Northern Hemisphere extratropics up to 80% greater than tropical eruptions, as decreases in aerosol lifetime are overwhelmed by the enhanced radiative impact associated with the relative confinement of aerosol to a single hemisphere. The model results are consistent with the temperature reconstructions, and elucidate how the radiative forcing produced by extratropical eruptions is strongly dependent on the eruption season and sulfur injection height within the stratosphere.

• Vogel, Andreas; Durant, Adam; Cassiani, Massimo; Clarkson, Rory J.; Slaby, Michal & Diplas, Spyridon [Show all 8 contributors for this article] (2019). Simulation of volcanic ash ingestion into a large aero engine: particle–fan interactions. Journal of turbomachinery. ISSN 0889-504X. 141(1). doi: 10.1115/1.4041464. Full text in Research Archive Show summary

  Volcanic ash (VA) clouds in flight corridors present a significant threat to aircraft operations as VA particles can cause damage to gas turbine engine components that lead to a reduction of engine performance and compromise flight safety. In the last decade, research has mainly focused on processes such as erosion of compressor blades and static components caused by impinging ash particles as well as clogging and/or corrosion effects of soft or molten ash particles on hot section turbine airfoils and components. However, there is a lack of information on how the fan separates ingested VA particles from the core stream flow into the bypass flow and therefore influences the mass concentration inside the engine core section, which is most vulnerable and critical for safety. In this numerical simulation study, we investigated the VA particle–fan interactions and resulting reductions in particle mass concentrations entering the engine core section as a function of particle size, fan rotation rate, and for two different flight altitudes. For this, we used a high-bypass gas-turbine engine design, with representative intake, fan, spinner, and splitter geometries for numerical computational fluid dynamics (CFD) simulations including a Lagrangian particle-tracking algorithm. Our results reveal that particle–fan interactions redirect particles from the core stream flow into the bypass stream tube, which leads to a significant particle mass concentration reduction inside the engine core section. The results also show that the particle–fan interactions increase with increasing fan rotation rates and VA particle size. Depending on ingested VA size distributions, the particle mass inside the engine core flow can be up to 30% reduced compared to the incoming particle mass flow. The presented results enable future calculations of effective core flow exposure or dosages based on simulated or observed atmospheric VA particle size distribution, which is required to quantify engine failure mechanisms after exposure to VA. As an example, we applied our methodology to a recent aircraft encounter during the Mt. Kelud 2014 eruption. Based on ambient VA concentrations simulated with an atmospheric particle dispersion model (FLEXPART), we calculated the effective particle mass concentration inside the core stream flow along the actual flight track and compared it with the whole engine exposure.

• Zavarsky, Alex; Booge, Dennis; Fiehn, Alina; Krüger, Kirstin; Atlas, Elliot & Marandino, Christa (2018). The influence of air-sea fluxes on atmospheric aerosols during the summer monsoon over the Indian Ocean. Geophysical Research Letters. ISSN 0094-8276. 45(1), p. 418–426. doi: 10.1002/2017GL076410. Full text in Research Archive
• Fiehn, Alina; Quack, Birgit; Marandino, Christa A. & Krüger, Kirstin (2018). Transport Variability of Very Short Lived Substances From the West Indian Ocean to the Stratosphere. Journal of Geophysical Research (JGR): Space Physics. ISSN 2169-9380. 123(10), p. 5720–5738. doi: 10.1029/2017JD027563. Full text in Research Archive Show summary

  Halogen- and sulfur-containing compounds are supersaturated in the surface ocean, which results in their emission to the atmosphere. These compounds can be transported to the stratosphere, where they impact ozone, the background aerosol layer, and climate. In this study we calculate the seasonal and interannual variability of transport from the West Indian Ocean (WIO) surface to the stratosphere for 2000–2016 with the Lagrangian transport model FLEXPART using ERA-Interim meteorological fields. We investigate the transport relevant for very short lived substances (VSLS) with tropospheric lifetimes corresponding to dimethylsulfide (1 day), methyl iodide (CH3I, 3.5 days), bromoform (CHBr3, 17 days), and dibromomethane (CH2Br2, 150 days). The stratospheric source gas injection of VSLS tracers from the WIO shows a distinct annual cycle associated with the Asian monsoon. Over the 16-year time series, a slight increase in source gas injection from the WIO to the stratosphere is found for all VSLS tracers and during all seasons. The interannual variability shows a relationship with sea surface temperatures in the WIO as well as the El Niño–Southern Oscillation. During boreal spring of El Niño, enhanced stratospheric injection of VSLS from the tropical WIO is caused by positive sea surface temperature anomalies and enhanced vertical uplift above the WIO. During boreal fall of La Niña, strong injection is related to enhanced atmospheric upward motion over the East Indian Ocean and a prolonged Indian summer monsoon season. Related physical mechanisms and uncertainties are discussed in this study. 1.

• Fiehn, Alina; Quack, Birgit; Stemmler, Irene; Ziska, Franziska & Krüger, Kirstin (2018). Importance of seasonally resolved oceanic emissions for bromoform delivery from the tropical Indian Ocean and west Pacific to the stratosphere. Atmospheric Chemistry and Physics (ACP). ISSN 1680-7316. 18(16), p. 11973–11990. doi: 10.5194/acp-18-11973-2018. Full text in Research Archive Show summary

  Oceanic very short-lived substances (VSLSs), such as bromoform (CHBr3), contribute to stratospheric halogen loading and, thus, to ozone depletion. However, the amount, timing, and region of bromine delivery to the stratosphere through one of the main entrance gates, the Indian summer monsoon circulation, are still uncertain. In this study, we created two bromoform emission inventories with monthly resolution for the tropical Indian Ocean and west Pacific based on new in situ bromoform measurements and novel ocean biogeochemistry modeling. The mass transport and atmospheric mixing ratios of bromoform were modeled for the year 2014 with the particle dispersion model FLEXPART driven by ERA-Interim reanalysis.We compare results between two emission scenarios: (1) monthly averaged and (2) annually averaged emissions. Both simulations reproduce the atmospheric distribution of bromoform from ship- and aircraft-based observations in the boundary layer and upper troposphere above the Indian Ocean reasonably well. Using monthly resolved emissions, the main oceanic source regions for the stratosphere include the Arabian Sea and Bay of Bengal in boreal summer and the tropical west Pacific Ocean in boreal winter. The main stratospheric injection in boreal summer occurs over the southern tip of India associated with the high local oceanic sources and strong convection of the summer monsoon. In boreal winter more bromoform is entrained over the west Pacific than over the Indian Ocean. The annually averaged stratospheric injection of bromoform is in the same range whether using monthly averaged or annually averaged emissions in our Lagrangian calculations. However, monthly averaged emissions result in the highest mixing ratios within the Asian monsoon anticyclone in boreal summer and above the central Indian Ocean in boreal winter, while annually averaged emissions display a maximum above the west Indian Ocean in boreal spring. In the Asian summer monsoon anticyclone bromoform atmospheric mixing ratios vary by up to 50% between using monthly averaged and annually averaged oceanic emissions. Our results underline that the seasonal and regional stratospheric bromine injection from the tropical Indian Ocean and west Pacific critically depend on the seasonality and spatial distribution of the VSLS emissions.

• Fujiwara, Masatomo; Wright, Jonathon S.; Manney, Gloria L.; Gray, Lesley J.; Anstey, James & Birner, Thomas [Show all 36 contributors for this article] (2017). Introduction to the SPARC Reanalysis Intercomparison Project (S-RIP) and overview of the reanalysis systems. Atmospheric Chemistry and Physics (ACP). ISSN 1680-7316. 17(2), p. 1417–1452. doi: 10.5194/acp-17-1417-2017. Full text in Research Archive Show summary

  The climate research community uses atmospheric reanalysis data sets to understand a wide range of processes and variability in the atmosphere, yet different reanalyses may give very different results for the same diagnostics. The Stratosphere–troposphere Processes And their Role in Climate (SPARC) Reanalysis Intercomparison Project (S-RIP) is a coordinated activity to compare reanalysis data sets using a variety of key diagnostics. The objectives of this project are to identify differences among reanalyses and understand their underlying causes, to provide guidance on appropriate usage of various reanalysis products in scientific studies, particularly those of relevance to SPARC, and to contribute to future improvements in the reanalysis products by establishing collaborative links between reanalysis centres and data users. The project focuses predominantly on differences among reanalyses, although studies that include operational analyses and studies comparing reanalyses with observations are also included when appropriate. The emphasis is on diagnostics of the upper troposphere, stratosphere, and lower mesosphere. This paper summarizes the motivation and goals of the S-RIP activity and extensively reviews key technical aspects of the reanalysis data sets that are the focus of this activity. The special issue "The SPARC Reanalysis Intercomparison Project (S-RIP)" in this journal serves to collect research with relevance to the S-RIP in preparation for the publication of the planned two (interim and full) S-RIP reports.

• Lennartz, Sinikka T.; Marandino, Christa A.; Hobe, Marc von; Cortes, Pau; Quack, Birgit & Simo, Rafel [Show all 14 contributors for this article] (2017). Direct oceanic emissions unlikely to account for the missing source of atmospheric carbonyl sulfide. Atmospheric Chemistry and Physics (ACP). ISSN 1680-7316. 17, p. 385–402. doi: 10.5194/acp-17-385-2017. Full text in Research Archive Show summary

  The climate active trace-gas carbonyl sulfide (OCS) is the most abundant sulfur gas in the atmosphere. A missing source in its atmospheric budget is currently suggested, resulting from an upward revision of the vegetation sink. Tropical oceanic emissions have been proposed to close the resulting gap in the atmospheric budget. We present a bottom-up approach including (i) new observations of OCS in surface waters of the tropical Atlantic, Pacific and Indian oceans and (ii) a further improved global box model to show that direct OCS emissions are unlikely to account for the missing source. The box model suggests an undersaturation of the surface water with respect to OCS integrated over the entire tropical ocean area and, further, global annual direct emissions of OCS well below that suggested by top-down estimates. In addition, we discuss the potential of indirect emission from CS2 and dimethylsulfide (DMS) to account for the gap in the atmospheric budget. This bottom-up estimate of oceanic emissions has implications for using OCS as a proxy for global terrestrial CO2 uptake, which is currently impeded by the inadequate quantification of atmospheric OCS sources and sinks.

• Fiehn, Alina; Quack, Birgit; Hepach, Helmke; Fuhlbrugge, Steffen; Tegtmeier, Susann & Toohey, Matthew [Show all 8 contributors for this article] (2017). Delivery of halogenated very short-lived substances from the west Indian Ocean to the stratosphere during the Asian summer monsoon. Atmospheric Chemistry and Physics (ACP). ISSN 1680-7316. 17, p. 6723–6741. doi: 10.5194/acp-17-6723-2017. Full text in Research Archive Show summary

  Halogenated very short-lived substances (VSLS) are naturally produced in the ocean and emitted to the atmosphere. When transported to the stratosphere, these compounds can have a significant influence on the ozone layer and climate. During a research cruise on RV Sonne in the subtropical and tropical West Indian Ocean in July and August 2014, we measured the VSLS, methyl iodide (CH3I) and for the first time bromoform (CHBr3) and dibromomethane (CH2Br2), in surface seawater and the marine atmosphere to derive their emission strengths. Using the Lagrangian transport model Flexpart with ERA-Interim meteorological fields, we calculated the direct contribution of observed VSLS emissions to the stratospheric halogen burden during Asian summer monsoon. Furthermore, we compare the in situ calculations with the interannual variability of transport from a larger area of the West Indian Ocean surface to the stratosphere for July 2000-2015. We found that the West Indian Ocean is a strong source region for CHBr3 (910 pmol m 2 h 1), very strong for CH2Br2 (930 pmol m 2 h 1), and average for CH3I (460 pmol m 2 h 1). The atmospheric transport from the tropical West Indian Ocean surface to the stratosphere experiences two main pathways. On very short timescales, especially relevant for the shortest-lived compound CH3I (3.5 days lifetime), convection above the Indian Ocean lifts oceanic air masses and VSLS towards the tropopause. On a longer timescale, the Asian summer monsoon circulation transports oceanic VSLS towards India and Bay of Bengal, where they are lifted with the monsoon convection and reach stratospheric levels in the southeastern part of the Asian monsoon anticyclone. This transport pathway is more important for the longer-lived brominated compounds (17 and 150 days lifetime for CHBr3 and CH2Br2). The entrainment of CHBr3 and CH3I from the West Indian Ocean to the stratosphere during Asian summer monsoon is less than from previous cruises in the tropical West Pacific Ocean during boreal autumn/early winter, but higher than from the tropical Atlantic during boreal summer. In contrast, the projected CH2Br2 entrainment was very high because of the high emissions during the West Indian Ocean cruise. The 16-year July time series shows highest interannual variability for the short-lived CH3I and lowest for the long lived CH2Br2. During this time period, a small increase of VSLS entrainment from the West Indian Ocean through the Asian monsoon to the stratosphere is found. Overall, this study confirms that the subtropical and tropical West Indian Ocean is an important source region of halogenated VSLS, especially CH2Br2, to the troposphere and stratosphere during the Asian summer monsoon.

• Schlundt, Cathleen; Tegtmeier, Susann; Lennartz, Sinikka T.; Bracher, Astrid; Cheah, Wee & Krüger, Kirstin [Show all 8 contributors for this article] (2017). Oxygenated volatile organic carbon in the western Pacific convective center: Ocean cycling, air-sea gas exchange and atmospheric transport. Atmospheric Chemistry and Physics (ACP). ISSN 1680-7316. 17(17), p. 10837–10854. doi: 10.5194/acp-17-10837-2017. Full text in Research Archive Show summary

  A suite of oxygenated volatile organic compounds (OVOCs – acetaldehyde, acetone, propanal, butanal and butanone) were measured concurrently in the surface water and atmosphere of the South China Sea and Sulu Sea in November 2011. A strong correlation was observed between all OVOC concentrations in the surface seawater along the entire cruise track, except for acetaldehyde, suggesting similar sources and sinks in the surface ocean. Additionally, several phytoplankton groups, such as haptophytes or pelagophytes, were also correlated to all OVOCs, indicating that phytoplankton may be an important source of marine OVOCs in the South China and Sulu seas. Humic- and protein-like fluorescent dissolved organic matter (FDOM) components seemed to be additional precursors for butanone and acetaldehyde. The measurement-inferred OVOC fluxes generally showed an uptake of atmospheric OVOCs by the ocean for all gases, except for butanal. A few important exceptions were found along the Borneo coast, where OVOC fluxes from the ocean to the atmosphere were inferred. The atmospheric OVOC mixing ratios over the northern coast of Borneo were relatively high compared with literature values, suggesting that this coastal region is a local hotspot for atmospheric OVOCs. The calculated amount of OVOCs entrained into the ocean seemed to be an important source of OVOCs to the surface ocean. When the fluxes were out of the ocean, marine OVOCs were found to be enough to control the locally measured OVOC distribution in the atmosphere. Based on our model calculations, at least 0.4 ppb of marine-derived acetone and butanone can reach the upper troposphere, where they may have an important influence on hydrogen oxide radical formation over the western Pacific Ocean.

• Vogel, Andreas; Diplas, Spyridon; Durant, Adam; Azar, Amin S.; Sunding, Martin Fleissner & Rose, William I. [Show all 10 contributors for this article] (2017). Reference data set of volcanic ash physicochemical and optical properties. Journal of Geophysical Research (JGR): Atmospheres. ISSN 2169-897X. 122(17), p. 9485–9514. doi: 10.1002/2016JD026328. Full text in Research Archive Show summary

  Uncertainty in the physicochemical and optical properties of volcanic ash particles creates errors in the detection and modeling of volcanic ash clouds and in quantification of their potential impacts. In this study, we provide a data set that describes the physicochemical and optical properties of a representative selection of volcanic ash samples from nine different volcanic eruptions covering a wide range of silica contents (50–80 wt % SiO2). We measured and calculated parameters describing the physical (size distribution, complex shape, and dense‐rock equivalent mass density), chemical (bulk and surface composition), and optical (complex refractive index from ultraviolet to near‐infrared wavelengths) properties of the volcanic ash and classified the samples according to their SiO2 and total alkali contents into the common igneous rock types basalt to rhyolite. We found that the mass density ranges between ρ = 2.49 and 2.98 g/cm3 for rhyolitic to basaltic ash types and that the particle shape varies with changing particle size (d < 100 μm). The complex refractive indices in the wavelength range between λ = 300 nm and 1500 nm depend systematically on the composition of the samples. The real part values vary from n = 1.38 to 1.66 depending on ash type and wavelength and the imaginary part values from k = 0.00027 to 0.00268. We place our results into the context of existing data and thus provide a comprehensive data set that can be used for future and historic eruptions, when only basic information about the magma type producing the ash is known.

• Ziska, Franziska; Quack, Birgit; Tegtmeier, Susann; Stemmler, Irene & Krüger, Kirstin (2016). Future emissions of marine halogenated very-short lived substances under climate change. Journal of Atmospheric Chemistry. ISSN 0167-7764. doi: 10.1007/s10874-016-9355-3. Full text in Research Archive
• Bittner, Matthias; Timmreck, Claudia; Schmidt, Hauke; Toohey, Matthew & Krüger, Kirstin (2016). The impact of wave-mean flow interaction on the Northern Hemisphere polar vortex after tropical volcanic eruptions. Journal of Geophysical Research (JGR): Atmospheres. ISSN 2169-897X. 121(10), p. 5281–5297. doi: 10.1002/2015JD024603. Full text in Research Archive
• Fuhlbrugge, Steffen; Quack, Birgit; Atlas, Elliot; Fiehn, Alina; Hepach, Helmke & Krüger, Kirstin (2016). Meteorological constraints on oceanic halocarbons above the Peruvian upwelling. Atmospheric Chemistry and Physics (ACP). ISSN 1680-7316. 16(18), p. 12205–12217. doi: 10.5194/acp-16-12205-2016. Full text in Research Archive
• Fuhlbrugge, Steffen; Quack, Birgit; Tegtmeier, Susann; Atlas, Elliot; Hepach, Helmke & Shi, Qiang [Show all 8 contributors for this article] (2016). The contribution of oceanic halocarbons to marine and free tropospheric air over the tropical West Pacific. Atmospheric Chemistry and Physics (ACP). ISSN 1680-7316. 16(12), p. 7569–7585. doi: 10.5194/acp-16-7569-2016. Full text in Research Archive
• Hossaini, R*; Patra, P.K.; Leeson, AA; Krysztofiak, G.; Abraham, NL & Andrews, SJ [Show all 44 contributors for this article] (2016). A multi-model intercomparison of halogenated very short-lived substances (TransCom-VSLS): Linking oceanic emissions and tropospheric transport for a reconciled estimate of the stratospheric source gas injection of bromine. Atmospheric Chemistry and Physics (ACP). ISSN 1680-7316. 16(14), p. 9163–9187. doi: 10.5194/acp-16-9163-2016. Full text in Research Archive
• Hepach, Helmke; Quack, Birgit; Tegtmeier, Susann; Engel, Anja; Bracher, Astrid & Fuhlbrugge, Steffen [Show all 11 contributors for this article] (2016). Biogenic halocarbons from the Peruvian upwelling region as tropospheric halogen source. Atmospheric Chemistry and Physics (ACP). ISSN 1680-7316. 16(18), p. 12219–12237. doi: 10.5194/acp-16-12219-2016. Full text in Research Archive
• Toohey, Matthew; Krüger, Kirstin; Sigl, Michael; Stordal, Frode & Svensen, Henrik (2016). Climatic and societal impacts of a volcanic double event at the dawn of the Middle Ages. Climatic Change. ISSN 0165-0009. 136(3), p. 401–412. doi: 10.1007/s10584-016-1648-7. Full text in Research Archive
• Lennartz, ST; Krysztofiak, G.; Marandino, C.A.; Sinnhuber, BM; Tegtmeier, S. & Ziska, F. [Show all 14 contributors for this article] (2015). Modelling marine emissions and atmospheric distributions of halocarbons and dimethyl sulfide: The influence of prescribed water concentration vs. prescribed emissions. Atmospheric Chemistry and Physics (ACP). ISSN 1680-7316. 15(20), p. 11753–11772. doi: 10.5194/acp-15-11753-2015. Full text in Research Archive
• Kutterolf, Steffen; Hansteen, Thor H.; Freundt, Armin; Wehrmann, Heidi; Appel, Karen & Krüger, Kirstin [Show all 7 contributors for this article] (2015). Bromine and chlorine emissions from Plinian eruptions along the Central American Volcanic Arc: From source to atmosphere. Earth and Planetary Science Letters. ISSN 0012-821X. 429, p. 234–246. doi: 10.1016/j.epsl.2015.07.064. Full text in Research Archive
• Tegtmeier, S.; Ziska, Franziska; Pisso, Ignacio; Quack, B; Velders, G. J. M. & Yang, X. [Show all 7 contributors for this article] (2015). Oceanic bromoform emissions weighted by their ozone depletion potential. Atmospheric Chemistry and Physics (ACP). ISSN 1680-7316. 15(23), p. 13647–13663. doi: 10.5194/acp-15-13647-2015. Full text in Research Archive Show summary

  At present, anthropogenic halogens and oceanic emissions of very short-lived substances (VSLSs) both contribute to the observed stratospheric ozone depletion. Emissions of the long-lived anthropogenic halogens have been reduced and are currently declining, whereas emissions of the biogenic VSLSs are expected to increase in future climate due to anthropogenic activities affecting oceanic production and emissions. Here, we introduce a new approach for assessing the impact of oceanic halocarbons on stratospheric ozone by calculating their ozone depletion potential (ODP)-weighted emissions. Seasonally and spatially dependent, global distributions are derived within a case-study framework for CHBr3 for the period 1999–2006. At present, ODP-weighted emissions of CHBr3 amount up to 50 % of ODP-weighted anthropogenic emissions of CFC-11 and to 9 % of all long-lived ozone depleting halogens. The ODP-weighted emissions are large where strong oceanic emissions coincide with high-reaching convective activity and show pronounced peaks at the Equator and the coasts with largest contributions from the Maritime Continent and western Pacific Ocean. Variations of tropical convective activity lead to seasonal shifts in the spatial distribution of the trajectory-derived ODP with the updraught mass flux, used as a proxy for trajectory-derived ODP, explaining 71 % of the variance of the ODP distribution. Future climate projections based on the RCP 8.5 scenario suggest a 31 % increase of the ODP-weighted CHBr3 emissions by 2100 compared to present values. This increase is related to a larger convective updraught mass flux in the upper troposphere and increasing emissions in a future climate. However, at the same time, it is reduced by less effective bromine-related ozone depletion due to declining stratospheric chlorine concentrations. The comparison of the ODP-weighted emissions of short- and long-lived halocarbons provides a new concept for assessing the overall impact of oceanic halocarbon emissions on stratospheric ozone depletion for current conditions and future projections.

• Krüger, Kirstin; Kutterolf, Steffen & Hansteen, Thor H. (2015). Halogen release from Plinian eruptions and depletion of stratospheric ozone. In Schmidt, Anja; Fristad, Kirsten & Elkins-Tanton, Linda T. (Ed.), Volcanism and global environmental change. Cambridge University Press. ISSN 9781107058378. p. 244–259. doi: 10.1017/cbo9781107415683.020. Full text in Research Archive
• Sigl, M; McConnell, Joseph R.; Toohey, Matthew; Curran, Mark A.J.; Das, Sarah B. & Edwards, Ross [Show all 16 contributors for this article] (2014). Insights from Antarctica on volcanic forcing during the common era. Nature Climate Change. ISSN 1758-678X. 4(8), p. 693–697. doi: 10.1038/nclimate2293. Full text in Research Archive
• Rex, M.; Wohltmann, I.; Ridder, T; Lehmann, R; Rosenlof, Karen H. & Wennberg, P [Show all 11 contributors for this article] (2014). A tropical West Pacific OH minimum and implications for stratospheric composition. Atmospheric Chemistry and Physics (ACP). ISSN 1680-7316. 14(9), p. 4827–4841. doi: 10.5194/acp-14-4827-2014. Full text in Research Archive
• Toohey, Matthew; Krüger, Kirstin; Bittner, Matthias; Timmreck, Claudia & Schmidt, Hauke (2014). The impact of volcanic aerosol on the Northern Hemisphere stratospheric polar vortex: mechanisms and sensitivity to forcing structure. Atmospheric Chemistry and Physics (ACP). ISSN 1680-7316. 14, p. 13063–13079. doi: 10.5194/acp-14-13063-2014. Full text in Research Archive
• Hepach, Helmke; Quack, Birgit; Ziska, F.; Fuhlbrügge, S.; Atlas, Elliot & Krüger, Kirstin [Show all 8 contributors for this article] (2014). Drivers of diel and regional variations of halocarbon emissions from the tropical North East Atlantic. Atmospheric Chemistry and Physics (ACP). ISSN 1680-7316. 14(3), p. 1255–1275. doi: 10.5194/acp-14-1255-2014. Full text in Research Archive
• Tegtmeier, S.; Krüger, Kirstin & al., , et (2013). The contribution of oceanic methyl iodide to stratospheric iodine. Atmospheric Chemistry and Physics (ACP). ISSN 1680-7316. 13, p. 11869–11886. doi: 10.5194/acp-13-11869-2013. Full text in Research Archive
• Hossaini, R*; al., , et & Krüger, Kirstin (2013). Evaluating global emission inventories of biogenic bromocarbons. Atmospheric Chemistry and Physics (ACP). ISSN 1680-7316. 13, p. 11819–11838. doi: 10.5194/acp-13-11819-2013. Full text in Research Archive
• Pfeilsticker, K.; Dorf, M.; Sturges, B.; Oram, D.; Engel, A. & Rex, M. [Show all 35 contributors for this article] (2013). The SHIVA Western Pacific campaign in fall 2011. Malaysian Journal of Science (MJS). ISSN 1394-3065. 32, p. 141–148. Full text in Research Archive
• Tegtmeier, S.; Hegglin, M.I.; Anderson, J.; Bourassa, A.; Brohede, S. & Degenstein, D. [Show all 27 contributors for this article] (2013). SPARC Data Initiative: A comparison of ozone climatologies from international satellite limb sounders. Journal of Geophysical Research (JGR): Atmospheres. ISSN 2169-897X. 118(21), p. 12,229–12,247. doi: 10.1002/2013JD019877. Full text in Research Archive
• Toohey, M*; Hegglin, M. I.; Tegtmeier, S.; Anderson, J; Anel, J.A. & Bourassa, A. [Show all 7 contributors for this article] (2013). Characterizing sampling biases in the trace gas climatologies of the SPARC Data Initiative. Journal of Geophysical Research (JGR): Atmospheres. ISSN 2169-897X. 118(20), p. 11,847–11,862. doi: 10.1002/jgrd.50874. Full text in Research Archive

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• Dijk, Evelien Van; Krüger, Kirstin; Sigl, Michael; Riede, Felix & Timmreck, Claudia (2025). The global impact of the 5624 BCE Mount Mazama eruption: The largest NH extratropical eruption of the Holocene. Full text in Research Archive
• Zoega, Tomas; Storelvmo, Trude & Krüger, Kirstin (2025). Arctic response to high-latitude effusive volcanic eruptions depends on the climate state. Full text in Research Archive
• Tjiputra, Jerry; Booge, Dennis; Krüger, Kirstin; Olivie, Dirk & Quack, Birgit (2024). Regional responses of marine bromoform emissions to future change. Full text in Research Archive
• Krüger, Kirstin & VIKINGS, Team (2024). Highlights from the VIKINGS project (Volcanoes, climate & society). Full text in Research Archive
• Dijk, Evelien Van; Riede, Felix; Timmreck, Claudia; Krüger, Kirstin & Sigl, Michael (2024). Extreme climatic and compound impacts of the Mount Mazama eruption. Full text in Research Archive
• Zoega, Tomas; Storelvmo, Trude & Krüger, Kirstin (2024). Climate response to the size and season of high-latitude, effusive volcanic eruptions. Full text in Research Archive
• Zoega, Tomas; Storelvmo, Trude & Krüger, Kirstin (2024). Surface climate response to the size and season of northern hemisphere, high latitude, effusive volcanic eruptions. Full text in Research Archive
• Burke, Andrea; Fuglestvedt, Herman Fæhn; Thomas, Liz; Marshall, Lauren & Krüger, Kirstin (2024). Revisiting the ‘transfer function’ of stratospheric sulfur loading from volcanic sulfate deposited on polar ice sheets. Full text in Research Archive
• Booge, Dennis; Tjiputra, Jerry; Olivie, Dirk Jan Leo; Quack, Birgit & Krüger, Kirstin (2024). Contrasting trends of marine bromoform emissions in a future climate. Full text in Research Archive
• Fuglestvedt, Herman Fæhn; Burke, Andrea & Krüger, Kirstin (2024). Refining volcanic forcing reconstructions Significance of the eruption season of northern extratropical eruptions. Full text in Research Archive
• Fuglestvedt, Herman Fæhn; Gabriel, Imogen; Sigl, Michael; Thordarson, Thorvaldur & Krüger, Kirstin (2024). Revisiting the 10th century Eldgjá eruption Modelling its climatic and environmental impacts. Full text in Research Archive
• Brodowsky, Christina Victoria; Barker, Simon; Sigl, Michael & Krüger, Kirstin (2024). Climatic and environmental impacts of an Oruanui-like supereruption in the Southern Hemisphere extratropics. Full text in Research Archive Show summary

  Explosive volcanic eruptions have disrupted the climate system dramatically in the past. Recent volcanological fieldwork suggests that at least four VEI 8 events took place in the past 100’000 years, depositing large amounts of volcanic volatiles onto polar ice sheets, each one with potentially significant impacts on human life on Earth. Previous studies on this research topic and time period tend to focus either on tropical eruptions or only consider changes in radiative forcing due to orbital parameters, solar variability, or changes in atmospheric CO2. Here, we seek to evaluate the climatic and environmental impacts of the ~25.5 ka Oruanui eruption (Taupō caldera, 38°S, 175°E, New Zealand). We thereby refine our understanding of the volcanic forcing based on volcanological and ice core data to provide a basis for long-term climate simulations. We use existing emission details for an idealized Oruanui-like eruption scenario. We run an ensemble of CESM2/WACCM simulations with 1850 pre-industrial conditions and instantaneously emit 260 Tg SO2, and the corresponding halogen load derived from petrological estimates into the stratosphere. We then analyze the climatic effects in the decades following the eruption compared with available paleo proxies. Our overarching goal is to provide comprehensive insights into the climatic and environmental repercussions of an Oruanui-like eruption, with a specific emphasis on the differences to tropical events of comparable magnitude. By comparing these two distinct types of eruptions, we aim to contribute to a refined understanding of volcanic impacts on Earth's climate and human life.

• Krüger, Kirstin; Dijk, Evelien Van; Jungclaus, Johann; Sigl, Michael & Timmreck, Claudia (2024). High-frequency climate forcing causes prolonged cold periods in the Holocene. Full text in Research Archive
• Krüger, Kirstin; Fuglestvedt, Herman Fæhn; Gabriel, Imogen; Sigl, Michael & Thordarson, Thorvaldur (2024). Revisiting the 10th-Century Eldgjá Eruption: Modeling the Climatic and Environmental Impacts. Full text in Research Archive Show summary

  The 10th-century Eldgjá eruption in Iceland is the largest basaltic flood lava eruption of the Common Era. However, the extent of its impacts is unclear due to limited historical records. By combining recent tephra analyses in volcanology and ice-core records, we present a gas emissions scenario for the Eldgjá eruption that spans 937 to 940 CE, co-injecting volcanic sulfur and halogens. The combined tropospheric and stratospheric sulfur emissions are 3-8 times higher than those adopted for Eldgjá in existing paleoclimate simulations. Earth system modeling of this scenario under pre-industrial conditions reveals a compound event with maximum northern extratropics surface cooling of ~2°C in summer-autumn of 939 and 940 CE, prolonged Arctic sea ice growth, and large-scale precipitation changes, concurrent with stratospheric ozone depletion and elevated pollution. These results imply that the combined climatic and environmental effects of the Eldgjá eruption may have significantly impacted human populations at the time.

• Krüger, Kirstin; Fuglestvedt, Herman Fæhn; Gabriel, Imogen; Sigl, Michael & Thordarson, Thorvaldur (2024). Revisiting the 10th-Century Eldgjá Eruption: Modeling the Climatic and Environmental Impacts. Full text in Research Archive Show summary

  The 10th-century Eldgjá eruption in Iceland is the largest basaltic flood lava eruption of the Common Era. However, the extent of its impacts is unclear due to limited historical records. By combining recent tephra analyses in volcanology and ice-core records, we present a gas emissions scenario for the Eldgjá eruption that spans 937 to 940 CE, co-injecting volcanic sulfur and halogens. The combined tropospheric and stratospheric sulfur emissions are 3-8 times higher than those adopted for Eldgjá in existing paleoclimate simulations. Earth system modeling of this scenario under pre-industrial conditions reveals a compound event with maximum northern extratropics surface cooling of ~2°C in summer-autumn of 939 and 940 CE, prolonged Arctic Sea ice growth, and large-scale precipitation changes, concurrent with stratospheric ozone depletion and elevated pollution. These results imply that the combined climatic and environmental effects of the Eldgjá eruption may have significantly impacted human populations at the time.

• Krüger, Kirstin (2023). Volcanic eruptions and viking society. [Internet]. https://www.sigma2.no/volcanic-eruptions-and-viking-society. Full text in Research Archive Show summary

  How did volcanic eruptions and their climate impact shape the early history and society of Scandinavia? .... Article is to be read at this link: https://www.sigma2.no/volcanic-eruptions-and-viking-society

• Oliviè, Dirk Jan Leo; Seland, Øyvind; Krüger, Kirstin & Schulz, Michael (2023). Analysis of NorESM2 full-chemistry simulation of the historical period (1850–2014). Full text in Research Archive
• Zanchettin, Davide; Timmreck, Claudia; Kohdri, Myriam; Hegerl, Gabi; Krüger, Kirstin & et, al. (2023). The Model Intercomparison Project on the Climatic Response to Volcanic Forcing (VolMIP): Status and Future Perspectives of the Initiative. Full text in Research Archive Show summary

  The Model Intercomparison Project on the climatic response to Volcanic forcing (VolMIP) is a protocol-driven international initiative under the umbrella of the sixth phase of the Coupled Model Intercomparison Project (CMIP6) aiming at coordinating the activities of different Research Institutes involved in numerical climate modelling focused on a multi-model assessment of climate models' performance under strong volcanic forcing conditions. The main objective of the initiative is to assess to what extent responses of the coupled ocean-atmosphere system to the same applied strong volcanic forcing are robustly simulated across state-of-the-art coupled climate models and identify the causes that limit robust simulated behavior, especially differences in their treatment of physical processes. To this purpose, four Tier-1 (mandatory) experiments branched into two main sets, named “volc-pinatubo” and “volc-long” were defined, together with eight more lower-priority experiments. Six years since the definition of the VolMIP protocol (Zanchettin et al., 2016), ensemble simulations of most of the mandatory VolMIP experiments have been completed and made publicly available through the Earth System Grid Federation open platform, with the first VolMIP results being currently published and several analyses in progress. The long turnover time between the experiment design, the integration of the simulations and the analysis of the output motivates an assessment of the overall effectiveness of the VolMIP strategy, particularly in the light of a possible second phase of the initiative. In this contribution, we will illustrate the status of the initiative, highlight its major achievements and discuss its future perspective in the light of emergent scientific questions regarding volcanically forced climate variability. Zanchettin, D., Khodri, M., Timmreck, C., Toohey, M., Schmidt, A., Gerber, E. P., Hegerl, G., Robock, A., Pausata, F. S. R., Ball, W. T., Bauer, S. E., Bekki, S., Dhomse, S. S., LeGrande, A. N., Mann, G. W., Marshall, L., Mills, M., Marchand, M., Niemeier, U., Poulain, V., Rozanov, E., Rubino, A., Stenke, A., Tsigaridis, K., and Tummon, F.: The Model Intercomparison Project on the climatic response to Volcanic forcing (VolMIP): experimental design and forcing input data for CMIP6, Geosci. Model Dev., 9, 2701–2719, https://doi.org/10.5194/gmd-9-2701-2016, 2016

• Booge, Dennis; Tjiputra, Jerry; Olivie, Dirk Jan Leo; Birgit, Quack & Krüger, Kirstin (2023). Global and regional marine bromoform emissions in a fully coupled ocean-atmosphere-model. Full text in Research Archive Show summary

  Bromoform (CHBr3) is one of the most important precursors of atmospheric reactive bromine with an atmospheric lifetime of ~20 days. Natural production, being the main source of oceanic CHBr3, is high at the coasts and in open ocean upwelling regions due to production by macroalgae and phytoplankton. Although highly relevant for the future halogen burden and ozone layer in the stratosphere, the global bromoform production in the ocean and their emissions are still poorly constrained in observations and are mostly neglected in Earth System Model (ESM) climate projections. Here, we show first model results of fully coupled ocean-atmosphere bromoform interactions in the Norwegian ESM (NorESM) with the ocean model BLOM and the ocean biogeochemistry component iHAMOCC for the CMIP6 historical period from 1850 to 2014. Our results are validated using oceanic and atmospheric measurements listed in the HalOcAt (Halocarbons in the Ocean and Atmosphere) data base and show an overall good agreement with those observations in open ocean regions. The NorESM open ocean emissions of CHBr3 are higher than previously published emission estimates from bottom-up approaches. Moreover, the emissions are mainly positive (sea-to-air fluxes) driven by the oceanic production, sea surface temperature and wind speed, dependent on season and location. However, during low-productive winter seasons, model results also show local negative fluxes (air-to-sea fluxes) in high latitudes, suggesting some oceanic regions to be a sink of atmospheric bromoform. Driving factors will be shown for different case studies, e.g. the tropical West Pacific, which is a hot spot for oceanic bromine delivery to the stratosphere. How to cite: Booge, D., Tjiputra, J., Olivié, D., Quack, B., Schulz, M., and Krüger, K.: Global and regional marine bromoform emissions in a fully coupled ocean-atmosphere-model, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-12225, https://doi.org/10.5194/egusphere-egu23-12225, 2023.

• Zoega, Tomas; Storelvmo, Trude & Krüger, Kirstin (2023). Surface Arctic warming from a high latitude effusive volcanic eruption. Full text in Research Archive
• Zoega, Tomas; Storelvmo, Trude & Krüger, Kirstin (2023). Can high latitude effusive volcanic eruptions cause surface winter warming in the Arctic? Full text in Research Archive
• Zoega, Tomas; Storelvmo, Trude & Krüger, Kirstin (2023). Arctic warming from a high latitude effusive volcanic eruption. Full text in Research Archive
• Zoega, Tomas; Storelvmo, Trude & Krüger, Kirstin (2023). Arctic warming from a high latitude effusive volcanic eruption. Full text in Research Archive
• Sigl, Michael; Fuglestvedt, Herman Fæhn; Krüger, Kirstin; Zhuo, Zhihong & et, al. (2023). Solar radiation management from Icelandic volcanoes during the Medieval Quiet Period. Full text in Research Archive
• Krüger, Kirstin & VIKINGS, Team (2023). Climatic and societal impacts in Scandinavia following the 536/540 CE volcanic double event. Full text in Research Archive
• Krüger, Kirstin & VIKINGS, Team (2023). Volcanic Eruptions and their Impacts on Climate and Society in 500-1250 CE. Full text in Research Archive
• Krüger, Kirstin (2023). Volcanic eruptions and Viking society. [Internet]. Sigma2. Full text in Research Archive Show summary

  Volcanic eruptions and the Viking society – The VIKINGS project and use of HPC resources

• Krüger, Kirstin & et, al. (2023). Initial meteorological conditions and eruption source parameters’ control on volcanic forcing and response. Full text in Research Archive
• Krüger, Kirstin & VIKINGS, Team (2023). VIKINGS: Volcanic Eruptions and their Impacts on Climate, Environment, and Viking Society in 500-1250 Common Era. Full text in Research Archive
• Fuglestvedt, Herman Fæhn; Zhuo, Zhihong; Toohey, Matthew & Krüger, Kirstin (2023). Arctic Polar Vortex Controls Aerosol Evolution After High-Latitude Volcanic Eruptions. Full text in Research Archive
• Fuglestvedt, Herman Fæhn; Gabriel, Imogen; Hutchison, William; Plunkett, Gill; Burke, Andrea & Sigl, Michael [Show all 8 contributors for this article] (2023). Impacts of the Icelandic Eldgjá eruption in 937-940 CE. Full text in Research Archive
• Krüger, Kirstin; Brenna, Hans; Fuglestvedt, Herman; Zhuo, Zhihong; Mills, Mike & Niemeier, Ulrike [Show all 7 contributors for this article] (2022). How large has a volcanic eruption to be to disrupt the QBO? Full text in Research Archive Show summary

  The dominating circulation phenomenon in the tropical stratosphere is the quasi-biennial oscillation (QBO), an approximately 28 months oscillation of alternating easterly or westerly winds centered at the equator. Volcanic aerosols may have an impact on the QBO phase as was observed for the Pinatubo eruption, which showed a “remarkably” prolonged Easterly wind regime. In contrast, geo-engineering studies model a prolonged Westerly phase or a shut-down of the QBO due to the artificial injection of sulfate aerosols. Extremely large volcanic eruptions which inject several 10s to 100s Tg SO2 might therefore have the potential to disturb the QBO. In addition, recent observations revealed two anomalous disruptions of the QBO in the 2010s with anomalous westerly winds probably due to Rossby wave propagating from the extratropics. We use an Earth System Model taking volcanic aerosol chemistry climate interactions into account to study the QBO response to violent volcanic eruptions. Simulating a tropical supereruption with 1000 Tg SO2 and halogens injection into the stratosphere reveals a disruption of the QBO for up to 10 years first with anomalous Easterlies followed by anomalous Westerlies before returning to a QBO regime with slightly longer period. Volcanic aerosol heating and ozone depletion cooling lead to the QBO disruption and anomalous wind regimes through radiation and wave-mean flow interactions. Here, we present a new set of sulfur- and halogen-rich volcanic eruptions experiments with 17 and 200 Tg SO2 injections into the tropical and Northern Hemisphere extratropics during January and July season to answer the above raised question.

• Krüger, Kirstin; Booge, Dennis; Quack, Birgit; Tjiputra, Jerry & Olivie, Dirk (2022). Future stratospheric halogen loading and ozone cycle: Modelling biogenic halocarbons in the ocean and their impact on the atmosphere. Full text in Research Archive Show summary

  Halogenated very short-lived substances (VSLSs) contribute to the tropospheric and stratospheric halogen burden, take part in ozone depletion, and, thus, impact climate. The contribution of oceanic VSLSs is estimated to be 10–40 % of the current total stratospheric bromine. Among them, is bromoform (CHBr3) one the most important precursor of atmospheric reactive bromine with a lifetime of ~20 days in the atmosphere. Oceanic sources of bromoform are highest at the coasts and in the open ocean in upwelling regions due to macroalgae and phytoplankton production. Although highly relevant for the future halogen burden and ozone layer in the stratosphere, the global bromoform production in the ocean and their emissions are still poorly constrained in observations and are mostly neglected in chemistry climate and Earth System Models (ESMs). Here, we show first model results following Stemmler et al (2015) but adding the full coupling of the oceanic bromoform production with the atmosphere through air-sea gas exchange and atmospheric chemistry in the Norwegian ESM (NorESM) with the ocean model BLOM and the biogeochemistry component iHAMOCC. We run NorESM for the CMIP6 historic scenario from 1850 to 2014. Our results reveal higher global bromoform emissions to the atmosphere than previously reported from bottom up approaches. Comparing our modelled bromoform results with HalOcAt observations reveal an overall good agreement for the open ocean and the seasonal cycle. Case studies for the tropical Indian Ocean and Pacific will be shown, which are hot spots in the ocean and for the stratospheric bromine delivery.

• Krüger, Kirstin & et, al (2022). Future stratospheric halogen loading and ozone cycle: Modelling biogenic halocarbons in the ocean and their impact on the atmosphere. Full text in Research Archive Show summary

  Halogenated very short-lived substances (VSLSs) contribute to the tropospheric and stratospheric halogen burden, take part in ozone depletion, and, thus, impact climate. The contribution of oceanic VSLSs is estimated to be 10–40 % of the current total stratospheric bromine. Among them, is bromoform (CHBr3) one the most important precursor of atmospheric reactive bromine with a lifetime of ~20 days in the atmosphere. Oceanic sources of bromoform are highest at the coasts and in the open ocean in upwelling regions due to macroalgae and phytoplankton production. Although highly relevant for the future halogen burden and ozone layer in the stratosphere, the global bromoform production in the ocean and their emissions are still poorly constrained in observations and are mostly neglected in chemistry climate and Earth System Models (ESMs). Here, we show first model results following Stemmler et al (2015) but adding the full coupling of the oceanic bromoform production with the atmosphere through air-sea gas exchange and atmospheric chemistry in the Norwegian ESM (NorESM) with the ocean model BLOM and the biogeochemistry component iHAMOCC. We run NorESM for the CMIP6 historic scenario from 1850 to 2014. Our results reveal higher global bromoform emissions to the atmosphere than previously reported from bottom up approaches. Comparing our modelled bromoform results with HalOcAt observations reveal an overall good agreement for the open ocean and the seasonal cycle. Case studies for the tropical Indian Ocean and Pacific will be shown, which are hot spots in the ocean and for the stratospheric bromine delivery.

• Zhuo, Zhihong; Fuglestvedt, Herman Fæhn; Toohey, Matthew; Mills, Michael J. & Krüger, Kirstin (2022). Impacts of tropical versus extratropical volcanic eruptions co-injecting sulphur and halogen to the stratosphere. Full text in Research Archive
• Zoega, Tomas; Storelvmo, Trude & Krüger, Kirstin (2022). Modelling the climate response to volcanic eruptions using a variable grid. Full text in Research Archive
• Zoega, Tomas; Storelvmo, Trude & Krüger, Kirstin (2022). Modelling the climate response to the 2014-15 Holuhraun eruption. Full text in Research Archive
• Zoega, Tomas; Storelvmo, Trude & Krüger, Kirstin (2022). Modelling the climate response to the 2014-15 Holuhraun eruption. Full text in Research Archive
• Sigl, Michael; Gabriel, Imogen & Krüger, Kirstin (2022). Timing of Holocene volcanic eruptions and their radiative aerosol forcing. Full text in Research Archive
• Krüger, Kirstin (2022). 536 “the worst year to be alive”? Full text in Research Archive
• Krüger, Kirstin; Fuglestvedt, Herman Fæhn; Dijk, Evelien Van; Zhuo, Zhihong; Sigl, Michael & Toohey, Matthew (2022). Modelling volcanic climate and environmental impacts and their signals in ice cores. Full text in Research Archive
• Krüger, Kirstin; Fuglestvedt, Herman Fæhn; Zhuo, Zhihong; Mills, Mike & Sigl, Michael (2022). Volcanic sulfate deposition to Greenland and Antarctica: A modeling sensitivity study with CESM(WACCM). Full text in Research Archive Show summary

  Reconstructions of the atmospheric sulfate aerosol burdens resulting from past volcanic eruptions are based on ice core-derived estimates of volcanic sulfate deposition and the assumption that the two quantities are directly proportional. Toohey et al (2013) modelled that the Antarctic and Greenland volcanic sulfate deposition is nonlinear for very large sulfur rich tropical eruptions (Tambora magnitude and larger), with significantly less sulfate deposition to Antarctica than to Greenland using the MAECHAM5-HAM aerosol-climate model. Here we test the relationship for simulations of explosive tropical and extratropical Northern Hemisphere volcanic eruptions by co-injecting sulfur and halogens into the stratosphere with the CESM2(WACCM) model including aerosol, chemistry, climate, and earth system processes. We consider different eruption parameters varying composition, latitude, season, injection height and magnitude. We run the model injecting 17 Tg and 200 Tg of SO2, together with scaled halogens, at 24 km altitude 15° N and 64° N during January and July pre industrial 1850 conditions. We will analyse the modelled sulphate deposition signals over Greenland and Antarctica and compare them to the volcanic ice core records of known eruptions of comparable strength during the Common Era and the Holocene. The analysis will focus on the deposition fluxes and their Greenland/Antarctica efficiencies in relation to the eruption parameters, sulphate aerosol transport, and the atmospheric circulation and deposition. With the help of the model data we will learn more about the volcanic sources to the sink processes, which will be helpful to better interpret volcanic signals in bipolar ice core records.

• Zhuo, Zhihong; Fuglestvedt, Herman Fæhn; Toohey, Matthew & Krüger, Kirstin (2022). Impacts of tropical versus extratropical volcanic eruptions with sulphur and halogen injections to the stratosphere. Full text in Research Archive
• Krüger, Kirstin (2022). VIKINGS: Volcanic Eruptions and their Impacts on Climate, Environment, and Viking Society in 500-1250 Common Era. Full text in Research Archive Show summary

  Welcome to the Geo-Wednesday in March! This month Kirstin Krüger, Professor at Meteorology and Oceanography, will give a talk about VIKINGS. VIKINGS is a multi-disciplinary project that aims to understand the role of volcanic eruptions and climate change in shaping the early history of Scandinavia. The period 500-1250 Common Era is characterized by societal unrest, Viking expansion, emerging kingship - and large volcanic eruptions evidenced by geochemical markers in natural archives. The climate variations in Europe, and especially in Scandinavia during this period, are however poorly resolved even on a timescale of centuries. Moreover, available dating of archeological findings from the time period have hardly been interpreted within a framework of climatic and environmental change. The VIKINGS project seeks to unravel the climate of this intriguing historic period and to address the role of volcanic eruptions impacting environmental and societal changes with a special focus on Southern Norway. Kirstin Krüger is a Professor in Meteorology at the UiO Department of Geosciences and the leader of the VIKINGS project – a Norwegian TOPPFORSK project. Her research focuses on stratospheric dynamics and the role of transport from climate relevant gases from the surface to the middle atmosphere. In the past 15 years, she has worked on large explosive volcanic eruptions and their impacts on climate, environment and society during present day and paleo time scales.

• Zhuo, Zhihong; Fuglestvedt, Herman Fæhn; Toohey, Matthew; Mills, Michael J & Krüger, Kirstin (2022). Impacts of tropical versus extratropical volcanic eruptions co-injecting sulphur and halogen to the stratosphere. Full text in Research Archive
• Zhuo, Zhihong; Fuglestvedt, Herman Fæhn & Krüger, Kirstin (2022). Impacts of tropical versus extratropical volcanic eruptions co-injecting sulfur and halogen to the stratosphere. Full text in Research Archive
• Tjiputra, Jerry; Booge, Dennis; Oliviè, Dirk Jan Leo; Quack, Birgit & Krüger, Kirstin (2022). Modeling bromoform in Norwegian Earth system model. Full text in Research Archive
• Hutchison, William; Krüger, Kirstin & et, al (2022). Timing and climate impact of Iceland’s largest basaltic eruptions: new insights from ice core archives. Full text in Research Archive
• Krüger, Kirstin & et, al (2022). Volcanic sulfate deposition to Greenland and Antarctica: A modeling sensitivity study with CESM(WACCM). Full text in Research Archive
• Krüger, Kirstin; Brenna, Hans & et, al (2022). How large has a volcanic eruption to be to disrupt the QBO? Full text in Research Archive Show summary

  The dominating circulation phenomenon in the tropical stratosphere is the quasi-biennial oscillation (QBO), an approximately 28 months oscillation of alternating easterly or westerly winds centered at the equator. Volcanic aerosols may have an impact on the QBO phase as was observed for the Pinatubo eruption, which showed a “remarkably” prolonged Easterly wind regime. In contrast, geo-engineering studies model a prolonged Westerly phase or a shut-down of the QBO due to the artificial injection of sulfate aerosols. Extremely large volcanic eruptions which inject several 10s to 100s Tg SO2 might therefore have the potential to disturb the QBO. In addition, recent observations revealed two anomalous disruptions of the QBO in the 2010s with anomalous westerly winds probably due to Rossby wave propagating from the extratropics. We use an Earth System Model taking volcanic aerosol chemistry climate interactions into account to study the QBO response to violent volcanic eruptions. Simulating a tropical supereruption with 1000 Tg SO2 and halogens injection into the stratosphere reveals a disruption of the QBO for up to 10 years first with anomalous Easterlies followed by anomalous Westerlies before returning to a QBO regime with slightly longer period. Volcanic aerosol heating and ozone depletion cooling lead to the QBO disruption and anomalous wind regimes through radiation and wave-mean flow interactions. Here, we present a new set of sulfur- and halogen-rich volcanic eruptions experiments with 17 and 200 Tg SO2 injections into the tropical and Northern Hemisphere extratropics during January and July season to answer the above raised question.

• Oliviè, Dirk Jan Leo; Seland, Øyvind; Krüger, Kirstin & Schulz, Michael (2022). Implementation of gas-phase chemistry in NorESM2. Full text in Research Archive
• Fuglestvedt, Herman Fæhn; Zhuo, Zhihong; Mills, Michael J. & Krüger, Kirstin (2021). Modelling the atmospheric impacts of high-latitude explosive volcanic eruptions. Full text in Research Archive
• Fuglestvedt, Herman Fæhn; Zhuo, Zhihong; Michael, Mills & Krüger, Kirstin (2021). Modelling the atmospheric impacts of high-latitude explosive volcanic eruptions. Full text in Research Archive
• Dijk, Evelien Van; Gundersen, Ingar Mørkestøl; Loftsgarden, Kjetil; Krüger, Kirstin & Iversen, Frode (2021). Can we link volcanic impacts on the climate to a change in society in Norway? Full text in Research Archive
• Dijk, Evelien Van & Krüger, Kirstin (2021). Large volcanic eruptions as a natural hazard: The impact of the 536/540 CE double event on the atmospheric circulation, surface climate, vegetation and society in Scandinavia. Full text in Research Archive
• Dijk, Evelien Van; Gundersen, Ingar Mørkestøl; Loftsgarden, Kjetil; Ballo, Eirik Gottschalk; Krüger, Kirstin & Iversen, Frode (2021). Can we link volcanic impacts on the climate to a change in society? Full text in Research Archive
• Dijk, Evelien Van & Krüger, Kirstin (2021). Impact of large volcanic eruptions on the 6th-7th century climate. Full text in Research Archive
• Tjoflot, Gunn Kristin; Krüger, Kirstin & Brenna, Hans (2021). Supervulkan kan endre vindsystemet i den tropiske stratosfæren. [Internet]. www.forskning.no. Full text in Research Archive Show summary

  Da Los Chocoyos i Guatemala hadde utbrudd for 84.000 år siden, kan utslipp av svovel og klor ha påvirket klimaet i lang tid, viser ny forskning.

• Fuglestvedt, Herman; Krüger, Kirstin; Zhuo, Zhihong; Sigl, Michael; Toohey, Matthew & Mills, Michael J. (2021). Modelling high-latitude explosive eruptions and their atmospheric and environmental impacts. Full text in Research Archive
• Zhuo, Zhihong; Fuglestvedt, Herman; Toohey, Matthew; Mills, Michael J. & Krüger, Kirstin (2021). Model comparison of volcanic aerosol forcing and climate impact of tropical and extratropical eruptions. Full text in Research Archive
• Schure, Anneke ter; Bajard, Manon Julietto Andree; Loftsgarden, Kjetil; Høeg, Helge Irgens; Ballo, Eirik Magnus Gottschalk & Bakke, Jostein [Show all 12 contributors for this article] (2021). Disentangling anthropogenic and environmental drivers of biological change in southeastern Norway during the Holocene. Full text in Research Archive
• Schure, Anneke ter; Bajard, Manon Julietto Andree; Loftsgarden, Kjetil; Høeg, Helge Irgens; Ballo, Eirik Magnus Gottschalk & Bakke, Jostein [Show all 12 contributors for this article] (2021). Anthropogenic and environmental drivers of biological change in southeastern Norway during the Holocene. Full text in Research Archive
• Bajard, Manon Julietto Andree; Ballo, Eirik Magnus Gottschalk; Høeg, Helge I.; Bakke, Jostein; Støren, Eivind N. & Loftsgarden, Kjetil [Show all 11 contributors for this article] (2021). Instability or adaptation of the pre-Viking society to the climate variability of the Late Antiquity? Full text in Research Archive Show summary

  Understanding how agricultural societies were impacted and adapted to past climate variations is critical to adapt to contemporary climate change and guaranty the food security. However, linking climate and change in the behaviour of a population are difficult to evidence. Here, we studied the climate variations of the period between 200 and 1300 CE and its impact on the pre-Viking and Viking societies in south Norway. We used a retrospective approach combining a multi-proxy analysis of lake sediments, including geochemical and palynological analyses, to reconstruct past changes in temperature and agricultural practices during the period 200-1300 CE. We associated variations in Ca/Ti ratio as a result of change in lake productivity with the temperature. The periods 200-300 and 800-1300 CE were warmer than the period between 300 and 800 CE, which is known as the “Dark Ages Cold Period” in the Northern Hemisphere. During this colder period, phases dominated by grazing activities (280-420 CE, 480-580 CE, 700-780 CE) alternated with phases dominated by the cultivation of cereals and hemp (before 280 CE, 420-480 CE, 580-700 CE, and after 800 CE). The alternation of these phases is synchronous of temperature changes. Cold periods are associated to livestock farming, and warmer periods to crop farming. This result suggests that when temperature no longer allowed crop farming, the food production specialized in animal breeding. The development of activities reached a maximum between 400 and 550 CE and a minimum between 680 and 800 CE, in agreement with archaeological findings. The Viking Age (800-1000 CE) started with an increase in temperature and corresponds to the warmest period between 200 and 1300 CE, allowing a larger development of the agriculture practices and society. Our results prove that the pre-Viking society adapted their agricultural practices to the climate variability of the Late Antiquity and that the Vikings expanded with climate warming.

• Tjoflot, Gunn Kristin; Brenna, Hans & Krüger, Kirstin (2021). Supervolcano eruption can change the periodic wind system in the tropical stratosphere. [Internet]. www.phys.org. Full text in Research Archive
• Zhuo, Zhihong; Fuglestvedt, Herman Fæhn & Krüger, Kirstin (2021). Impacts of tropical versus extratropical volcanic eruptions (including volcanic sulphur and halogen injections). Full text in Research Archive
• Zhuo, Zhihong; Fuglestvedt, Herman Fæhn; Toohey, Matthew; Mills, Michael J. & Krüger, Kirstin (2021). Model comparison of stratospheric aerosol forcing of tropical and extratropi-cal volcanic eruptions. Full text in Research Archive Show summary

  Major volcanic eruptions, as one of the natural forcing, increase sulfate aerosols in the stratosphere. The stratospheric aerosol forcing differs from tropical and extratropical eruptions, and depends on the eruption season and height, and volcanic volatile injections. In order to study different aerosol forcing and their impact, we perform simulations based on the fully coupled Community Earth System Model version 2 (CESM2) with the Whole Atmosphere Community Climate Model version 6 (WACCM6) with prognostic stratospheric aerosol and chemistry. Explosive eruptions at 14.6 N and 63.6 N in January and July injecting 17 Tg and 200 Tg SO2 at 24 km with and without halogens are simulated, in line with Central American Volcanic Arc and Icelandic volcanic eruptions. Simulated changes in the stratospheric sulfate and halogen burdens, and impacts on aerosol optical depth and ozone are analyzed.

• Zhuo, Zhihong; Fuglestvedt, Herman Fæhn; Toohey, Matthew; Mills, Michael J. & Krüger, Kirstin (2021). Model comparison of aerosol forcing and impactof tropicaland extratropical eruptions. Full text in Research Archive
• Sigl, Michael; Krüger, Kirstin & al, More authors Et (2021). Insights on the timing, global sulfate lifecycle an􀀀 climate impact of Earth's largest (pre-) historic volcanic eruptions. EGU General Assembly. EGU21-946. doi: 10.5194/egusphere-egu21-946,2021. Full text in Research Archive Show summary

  Extratropical volcanic eruptions are commonly thought to be less effective at driving large-scale surface cooling than tropical eruptions, and only the latter are commonly thought to be able to distribute sulfate globally. Here, we test both of these assumptions using a network of ice cores from the polar regions of Antarctica and Greenland covering the past 15’000 years and climate-aerosol modeling. We employ state-of-the-art analyses of trace elements, cryptoptephra and sulphur isotopes (Burke et al., 2019) to gain new insights into the timing of past eruptions, their stratospheric sulphur mass injections and subsequent sulphate aerosol lifecycle. We use this information to estimate the climate impact potential due to negative radiative forcing caused by Earth’s largest volcanic eruptions since the last Glacial. Our analysis encompasses over 1’000 eruptions and include the caldera-forming eruptions of Okmok II (Alaska, 43 BCE, VEI=6, 53°N; McConnell et al., 2020), Aniakchak II (Alaska, 1600s BCE, VEI=6, 57°N), Crater Lake (Mazama, Oregon, 5600s BCE, VEI=7, 43°N) and Laacher See (Germany, c. 13 ka BP, VEI=6, 50°N). We use our reconstructed radiative forcing and the coupled earth system models MPI-ESM1.2 and CESM (version 1.2.2) to analyze the climatic impact caused by these eruptions and compare the simulated temperature response with temperature reconstructions based on ultra-long tree-ring chronologies. Finally, based on these comparisons, we propose a number of stratigraphic age tie-points to anchor ice-core chronologies from Greenland (GICC05) and Antarctica (WD2014) to the absolute dated tree-ring chronology. We thereby aim to improve proxy synchronization throughout the Holocene -- a prerequisite for detection and attribution studies -- and invite the paleo-climate community to update climate proxy records based on ice cores to the latest chronologies. The European Research Council Grant 820047 under the European Union’s Horizon 2020 research and innovation program funded the research project THERA - Timing of Holocene Volcanic eruptions and their radiative aerosol forcing.

• Krüger, Kirstin & al, More authors Et (2021). Modeling sulfur- and halogen-rich supereruptions impacts on the atmosphere, climate and environment. Full text in Research Archive
• Krüger, Kirstin & VIKINGS, Team (2021). VIKINGS: Volcanic Eruptions and their Impacts on Climate, Environment, and Viking Society in 500-1250 Common Era. Full text in Research Archive
• Krüger, Kirstin & al, More authors Et (2021). Modeling sulfur- and halogen-rich eruptions impacts on the atmosphere, climate and environment. Full text in Research Archive
• Krüger, Kirstin (2020). Volcanic Eruptins and their Impacts on Climate, Environment, and Viking Society in 500-1250 CE. Full text in Research Archive Show summary

  This multi-disciplinary project aims to understand the role of volcanic eruptions and climate change in shaping the early history of Europe. The period 500-1250 CE is characterized by natural disasters, societal unrest, Viking expansion, emerging kingship – and large volcanic eruptions evidenced by geochemical markers in natural archives. Contemporary reports of a mysterious cloud which dimmed the light of the sun for at least a year were written at the dawn of the Middle Ages which marked the beginning of an unusual cold period in the mid of the 6th century due to the double volcanic eruption event in 536/540 CE. The social structure of Scandinavian society was radically changed between 500 and 750 CE. Population levels were reduced by plague and agriculture had to be adapted to a colder climate. Tree ring and climate model data from Scandinavia identify a prolonged period of cooling which may have lasted over a century. Following is a period of volcanic activity which was thought to be more quiescent in a global sense and is marked by the onset of the medieval warm period (c. 950 -1250 CE). However, volcanic eruptions in Iceland were frequently active during 700 to 1100 CE and must have had severe impacts on climate, environment and society in Northern Europe, which is not supported by available records. This presentation aims to shed more light into the background of this early Common Era period based on revised volcanic forcing, complex earth system climate model, proxy, and archaeology data.

• Dijk, Evelien Van & Krüger, Kirstin (2020). Was there a volcanic induced long lasting cooling in the mid 6th-7th century? Full text in Research Archive
• Dijk, Evelien Jacoba Cornelia Van & Krüger, Kirstin (2020). Impact of the 536/540 CE double volcanic eruption event on the 6th-7th century climate using model and proxy data. Full text in Research Archive
• Dijk, Evelien Jacoba Cornelia Van & Krüger, Kirstin (2020). The impact of the 536/540 CE double volcanic eruption event on the climate. Full text in Research Archive
• Dijk, Evelien Jacoba Cornelia Van & Krüger, Kirstin (2020). Impact of the 536/540 CE double eruption event on the 6th -7th century climate using model and proxy data. Full text in Research Archive
• Bajard, Manon Julietto Andree; Ballo, Eirik Magnus Gottschalk; Støren, Eivind Wilhelm Nagel; Bakke, Jostein; Høeg, Helge Irgens & Loftsgarden, Kjetil [Show all 8 contributors for this article] (2020). Volcanic Eruptions and their Impacts on Climate, Environment, and Viking Society in 500-1250 CE. Full text in Research Archive
• Bajard, Manon Julietto Andree; Ballo, Eirik Magnus Gottschalk; Støren, Eivind Wilhelm Nagel; Bakke, Jostein; Høeg, Helge Irgens & Loftsgarden, Kjetil [Show all 9 contributors for this article] (2020). Record of climate and environmental changes in a dead-ice lake close to Gardermoen told by a 10 000 years old freshwater fish and a Viking King. Full text in Research Archive Show summary

  We studied a six-meter long sediment sequence retrieved from the kettle lake Ljøgottjern, close to Oslo-Gardermoen Airport, to reconstruct environmental and climate changes during the last millennia. The lake is 18 m depth and located at 185 m a.s.l., under the maximum postglacial sea level. The largest burial mound of Northern Europe was built in the mid-6th century on the shore of this lake allegedly for King Rakni and makes this place ideal to study human-environment interactions in a paleo-perspective approach. Using a multi-proxy sedimentological analysis of this record, including 14C dating, paleo-secular variations, XRF and CT scans, and pollen, this study highlights different climate patterns throughout the Holocene. At the bottom of the core, a carbonated sandy-clayey layer with centimetric twigs overlays an organic rich black peaty-type layer, suggesting a continental environment. On top of that, a disturbed clay layer containing fish bones from a freshwater Carpinidae species was found. The fish could have been buried by the massive (70 cm) sandy carbonated deposit covering it. A sharp transition separates a clay cap on top of the deposit and the start of a finely laminated lacustrine sedimentation dated 9.3 ka cal. BP. The massive deposit could be associated to the outburst flood from the glacial lake Nedre Glomsjø dated 10-10.4 ka cal BP (Longva, 1984; Høgaas and Longva, 2016). A major change in the sedimentation occurred around 8 ka cal. BP, with darker sediments and a lower sedimentation rate. This change could be related to a warming climate and stabilization of the catchment by soil and forest development around the lake in the mid-Holocene. The sedimentation rate increased again between 2000 and 3000 years cal. BP as a result of the development of first human activities and major change in the vegetation (Høeg, 1997). We reconstructed temperature changes during the first millennia and compared it to societal dynamics. The period between 300 and 800 years cal. CE is colder than the period 800-1300 years cal. CE. After 1600 years cal. CE, an increase in erosion could be associated to the extension of the population and agriculture in Scandinavia and revealed a chronicle of the major floods in this area. The presence of freshwater fish older than 9,3 ka attests of their early and natural colonization of Scandinavian lakes. The comparison of this record with archaeological data will allow us to discuss socio-environmental dynamics following the deglaciation in the area. References: Smith, A.A. 2010. CO2 stor¬age. Journal of Sciences 32, 10-20. Høeg, H.I., 1997. Pollenanalytiske undersøkelser på Øvre Romerike : Ullensaker og Nannestad, Akershus fylke : Gardermoprosjektet, Varia (Universitetets oldsaksamling : trykt utg.). Universitetets oldsaksamling, Oslo. Høgaas, F., Longva, O., 2016. Mega deposits and erosive features related to the glacial lake Nedre Glomsjø outburst flood, southeastern Norway. Quat. Sci. Rev. 151, 273–291. https://doi.org/10.1016/j.quascirev.2016.09.015 Longva, O., 1984. Romeriksmjelen danna ved ein storflaum på Austlandet for vel 9000 år siden. Norges geologiske undersøkelse, Årsmelding 1984 8–11.

• Bajard, Manon Julietto Andree; Ballo, Eirik Magnus Gottschalk; Støren, Eivind Wilhelm Nagel; Bakke, Jostein; Høeg, Helge Irgens & Loftsgarden, Kjetil [Show all 9 contributors for this article] (2020). Tracing socio-environmental dynamics and climate changes in the period 300-1300 CE in Scandinavia from lake sediments. Full text in Research Archive Show summary

  Understanding large volcanic eruptions impacts on environments and societies is necessary to consider future climate and socio-environmental interactions. Lake sediments can record these dynamics on a continuous long time scale and include at the same time footprints from volcanic eruptions, climate changes and human activities. We analysed the sediments of Lake Ljøgottjern, located southeastern Norway. The largest burial mound of Northern Europe was built in the mid-6th century on the shore of this lake and makes this place an ideal site to study human-environmental interactions throughout the last millennia. Using a multi-proxy analysis of this sedimentary record, including 14C dating, geochemistry, as well as palynological data, we reconstructed temperature and socio-environmental changes in this area between 300 and 1300 CE (Common Era). We associated changes in Ca/Ti ratio with changes in temperature. The period between 300 and 800 CE was colder than the periods 200-300 and 800-1300 CE. Five abrupt cooling events seem to be linked to weakened positive NAO (North Atlantic Oscillation) phases, and two of them can also be linked to the two largest volcanic events of the period (i.e. the 536/540 CE double event, and 1257 CE eruption of Samalas). Palynological data indicate a decrease of the human activities and reforestation of the area in the 6th century. This abandonment is consistent with archaeological findings and could be related to the 536/540 cooling event. Very little activities are then recorded between 700 and 850 CE. Agricultural activities start again strongly in the Viking age with increase in temperature.

• Krüger, Kirstin & Bajard, Manon Julietto Andree (2019). Volcanic Eruptions and their Impacts on Climate, Environment, and Viking Society in 500-1250 CE. Full text in Research Archive Show summary

  VIKINGS(NFR) TACCO(Notur/NorStore)

• Krüger, Kirstin; Sigl, Michael; Toohey, Matthey & Iversen, Frode (2019). Volcanic Eruptions and their Impacts on Climate, Environment, and Viking Society in 500-1250 CE. Full text in Research Archive
• Krüger, Kirstin (2019). Volcanic Eruptions and their Impacts on Climate, Environment, and Viking Society in 500-1250 CE. Full text in Research Archive
• Krüger, Kirstin (2019). Working Group Overview. Full text in Research Archive Show summary

  VIKINGS/NFR TACCO INES KeyCLIM

• Brenna, Hans; Kutterolf, Steffen; Mills, Michael; Niemeier, Ulrike; Timmreck, Claudia & Krüger, Kirstin (2019). The Los Chocoyos super volcanic eruption disrupts the Quasi-Biennial Oscillation. Full text in Research Archive Show summary

  The Los Chocoyos super eruption happened ~81 kyrs ago in Guatemala, and was one of the largest eruptions of the past 100,000 years. The eruption emitted enormous amounts of sulfur, chlorine and bromine, with multi-decadal consequences for the global climate and environment (Brenna et al 2019 ACPD). In this paper, we simulate the impact of this sulfur- and halogen-rich super-eruption on the quasi-biennial oscillation (QBO), an oscillation of the zonal winds in the tropical stratosphere, with the comprehensive aerosol chemistry Earth System Model CESM2(WACCM6). We find a ~10 year disruption of the QBO before returning to QBO conditions with a slightly prolonged periodicity. Volcanic induced aerosol heating and ozone depletion cooling leads through radiative changes and wave-mean flow interactions to the QBO disruption and anomalous wind regimes. Different model ensembles, volcanic forcing scenarios and one other model backs up the robustness of our results.

• Krüger, Kirstin (2019). The sulfur- and halogen-rich super eruption Los Chocoyos and its impacts on climate, environment, and circulation. Full text in Research Archive Show summary

  The Los Chocoyos super eruption happened ~81 kyrs ago in Guatemala, and was one of the largest eruptions of the past 100,000 years. The eruption emitted enormous amounts of sulfur, chlorine and bromine with consequences for the global climate, environment and atmospheric circulation. Using the Earth System Model CESM2(WACCM6) we simulate the impacts of this super eruption on the pre-industrial Earth System. Our model results show that the ozone layer nearly collapses, with large impacts on UV and the biosphere, and the surface climate cools globally with >6 K. Recovery to pre-eruption ozone levels and climate takes 15 and 30 years respectively. The quasi-biennial oscillation (QBO), an oscillation of the zonal winds in the tropical stratosphere with ~28 month periodicity, reveals a 10 year disruption before returning to QBO conditions with a slightly prolonged periodicity. Different model ensembles, volcanic forcing scenarios and comparison with other models are used to test the robustness of our results.

• Fouilloux, Anne Claire; Iaquinta, Jean & Krüger, Kirstin (2019). Towards an infrastructure for Earth system modelling in Norway. Full text in Research Archive
• Fouilloux, Anne Claire; Krüger, Kirstin & Iaquinta, Jean (2019). Climate Analysis with Galaxy. Full text in Research Archive Show summary

  Advance in the development of climate models and associated data viewers and processing tools has achieved unprecedented maturity in the environmental scientific community. This progress was accompanied by the standardization of model output formats (conventions for Climate and Forecast metadata), the availability of open databases (i.e., the Earth System Grid Federation), and of the climate model codes themselves. However, scientific communities are not fully realizing the benefits of such advances because of the complexity for both running and analysing climate models. Using Galaxy makes it possible to share tools and easily (re-)run climate model runs or analyse climate data thus opening new opportunities for multidisciplinary research for instance ecology, social and human sciences. In this presentation, we will show how climate models can be run out-of-the-box, without much effort, using Galaxy platform. We will show how climate model outputs can be visualized using the same web portal.

• Krüger, Kirstin; Iversen, Frode; Jahren, Anne, Hope & Svensen, Henrik Hovland (2018). Volcanic Eruptions and their Impacts on Climate, Environment, and Viking Society in 500-1250 CE. Full text in Research Archive
• Krüger, Kirstin; Iversen, Frode; Jahren, Anne, Hope & Svensen, Henrik Hovland (2018). Volcanic Eruptions and their Impacts on Climate, Environment, and Viking Society in 500-1250 CE. Full text in Research Archive
• Krüger, Kirstin; Iversen, Frode; Jahren, Anne, Hope & Svensen, Henrik Hovland (2018). Volcanic Eruptions and their Impacts on Climate, Environment, and Viking Society in 500-1250 CE. Full text in Research Archive
• Krüger, Kirstin; Iversen, Frode; Jahren, Anne, Hope & Svensen, Henrik Hovland (2018). Volcanic Eruptions and their Impacts on Climate, Environment, and Viking Society in 500-1250 CE. Full text in Research Archive
• Brenna, Hans; Kutterolf, Steffen; Mills, Michael J & Krüger, Kirstin (2018). Atmospheric, climatic and environmental effects of the super-size Los Chocoyos eruption 84 kyrs ago. Full text in Research Archive Show summary

  The Los Chocoyos eruption (Magnitude ~8, dated to 84 kyrs before present) was one of the largest volcanic eruptions during the past 100,000 years. Originating from present-day Guatemala, the eruption formed the current stage of the large Atitlán caldera. Los Chocoyos released more than ~1100 km3 of tephra and the eruption is used as a widespread stratigraphic key marker during that time. The ash layers can be found in marine deposits from offshore Ecuador to Florida over an area of more than 107 km2. Using the new erupted magma mass from Kutterolf et al (2016) and recent volatile measurements (Metzner et al 2014, Krüger et al 2015, Kutterolf et al 2015) we estimate that the Los Chocoyos eruption released >1045 Mt SO2, ~1200 megatons of chlorine, and ~2 megatons of bromine, which classifies it as a super-size eruption. Considering these volatile emissions, the eruption must have caused massive effects on the atmosphere, climate and environment at that time, e.g. pronounced and long lasting ozone depletion with impacts on surface ultraviolet radiation. We will present results of the impact of volatile injections from the super-size Los Chocoyos eruption on atmospheric composition, chemistry and radiation. We will use the newly developed coupled chemistry climate model CESM2(WACCM) taking the combined effect of both sulfur and halogen interactively into account. The model results will be compared with a sulfur-rich only volcanic eruption. The analysis will focus in particular on halogen and ozone chemistry, radiation, atmospheric circulation and surface climate changes.

• Brenna, Hans; Kutterolf, Steffen; Mills, Michael J & Krüger, Kirstin (2018). Are we ready for the next big sulfur-and-halogen-rich eruption in the tropics? Full text in Research Archive Show summary

  Large Plinian volcanic eruptions inject large amounts of gases (e.g. S, Cl, Br) and solid particles into the stratosphere. If the eruption occurs in the tropics, it can have a global impact due to the dispersal through the large scale meridional overturning circulation. Previous modeling studies mainly concentrate on the sulfate aerosol effects on climate and ozone. In contrast, the role of volcanic halogens from tropical eruptions is believed to play an insignificant role for the global atmosphere, based on observations from the 1982 El Chichón and 1991 Pinatubo eruptions. New measurements regarding the halogen release by paleo Plinian eruptions (Kutterolf et al. 2015), as well as recent volcanic plume observations and model simulations facilitate our investigation into what effect the combined sulfur, chlorine and bromine emissions from large tropical eruptions have on ozone and the atmosphere in general. The post-Pinatubo period has been volcanically relatively quiet. This means that there are few well-observed large eruptions that can be used as input to modeling studies. Using the large and almost complete eruptive data set from the Central American Volcanic Arc (CAVA) of the last 200 ka, we can construct well constrained input-values to chemistry-climate model simulations. This past record suggests that a future Plinian CAVA eruption will release large amounts of sulfur and halogen. As the chlorine content of the atmosphere decreases during the 21th century future sulfur-and-halogen-rich eruptions will have a large impact on stratospheric ozone and climate. We will present results from the coupled chemistry climate model CESM(WACCM) of different CAVA eruption strength containing sulfur, chlorine and bromine and their impact on stratospheric ozone. We argue that if humanity wants to be prepared for the next big tropical eruption we need also take volcanic halogens into account due to their potentially large impact on stratospheric composition and chemistry.

• Brenna, Hans; Kutterolf, Steffen & Krüger, Kirstin (2018). Global ozone depletion and increase of UV radiation caused by pre-industrial tropical volcanic eruptions. Full text in Research Archive Show summary

  Abstract Large explosive tropical volcanic eruptions inject significant amounts of gases into the stratosphere, where they disperse globally through the large-scale meridional circulation. Halogens from tropical eruptions have been thought to be negligible based on observations of the largest eruptions of the satellite era, and thus most studies focus on sulfuric acid aerosols. More recent observations and plume modeling indicate that explosive volcanism can be a big source of halogens to the stratosphere. Here, we present the first study, based on observations, of sulfur, chlorine and bromine releases from tropical volcanic eruptions from the Central American Volcanic Arc over the last 200 ka combined with state-of-the-art coupled chemistry climate model simulations using CESM1(WACCM). The simulations reveal global, long-lasting impact on the ozone layer affecting atmospheric composition and circulation for a decade. Column ozone drops below 220 DU (ozone hole conditions) in the tropics, Arctic and Antarctica, increasing biologically active UV by 80 to 400%. Given the current decline in anthropogenic chlorine, halogen and sulfur rich explosive tropical eruptions may become the major threat to the future ozone layer.

• Fiehn, Alina; Krüger, Kirstin; Stemmler, Irene; Quack, Birgit & Ziska, Franziska (2018). Importance of seasonally resolved oceanic emissions for bromoform delivery to the stratosphere through the Asian monsoon. Full text in Research Archive Show summary

  Very short-lived substances (VSLS) of marine origin, such as bromoform (CHBr3), contribute to stratospheric bromine loading and, thus, to ozone depletion. However, amount, timing, and region of bromine delivery to the stratosphere through one of the main entrance gates, the Asian monsoon circulation, are still uncertain. The atmospheric distribution of bromoform and its delivery to the stratosphere have been the topic of several chemistry transport and chemistry climate modeling studies, but only few studies considered seasonally varying surface water concentrations or emissions in their model simulations. In this study, we create two bromoform emission inventories with monthly resolution for the tropical Indian Ocean and West Pacific based on new in situ bromoform measurements in the tropical West Indian Ocean (Fiehn et al., 2017) incorporated into the observation based climatology (Ziska et al., 2013), and the ocean biogeochemistry modeling (Stemmler et al., 2015) of bromoform. Mass transport and atmospheric mixing ratios of bromoform are simulated for the year 2014 with the particle dispersion model FLEXPART driven by ERA-Interim reanalysis. Model experiments are performed with two emission scenarios: (1) monthly varying emissions and (2) constant emissions over the whole year. We compare these model results with ship- and aircraft-based observations in the boundary layer and upper troposphere lower stratosphere. Using monthly emissions, main oceanic source regions for the stratosphere include the Arabian Sea and Bay of Bengal in boreal summer and the tropical west Pacific Ocean in boreal winter. The corresponding main stratospheric injection occurs over the southern tip of India in boreal summer associated with the high local oceanic sources and strong convection of the summer monsoon. The annually averaged stratospheric injection of bromoform is in the same range independent of temporal resolution of the emissions. However, monthly emissions result in highest mixing ratios within the Asian monsoon anticyclone in boreal summer and above the central Indian Ocean in boreal winter, while constant emissions show a maximum above the West Indian Ocean in boreal spring. Our results for the Asian monsoon circulation underline that the seasonal and regional stratospheric bromine injection from the tropical Indian Ocean and west Pacific critically depends on the seasonality and spatial distribution of the VSLS emissions next to the variability in the atmospheric transport. Finally, we discuss our results with respect to circulation changes of the Asian monsoon which shows an increase in bromoform delivery between 2000 and 2015.

• Krüger, Kirstin (2018). Does the ocean impact the ozone layer? Full text in Research Archive Show summary

  Natural, halogenated very short-lived substances (VSLS) with an atmospheric lifetime τ<0.5 yr play an important role in the stratospheric ozone budget besides the anthropogenic long-lived chlorine- and brominefluorocarbons. The tropical oceans are a known source of reactive iodine and bromine to the atmosphere such as the VSLS methyl iodide (CH3I), bromoform (CHBr3), and dibromomethane (CH2Br2). They contribute to the halogen loading of the stratosphere if they are transported fast enough within, i.e., deep tropical convection. The tropical West Pacific and Indian Ocean are of special interest since the oceanic compounds of the VSLS are projected to have hot spots for both their emissions and transport pathways to the stratosphere. This study will give an overview of 10 years of research work on VSLS sources in the tropical oceans and their transport pathways and contribution to the stratospheric halogen level to answer the question.

• Fiehn, Alina; Gjermo, Sarah; Fuhlbrugge, Steffen; Quack, Birgit; Marandino, Christa A. & Atlas, Elliot L [Show all 7 contributors for this article] (2017). SO243 ASTRA-OMZ: Does ENSO influence the transport of halogenated very short-lived substances above the tropical East Pacific? Full text in Research Archive
• Brenna, Hans; Krüger, Kirstin & Kutterolf, Steffen (2017). A new threat to the future ozone layer? Halogen and sulfur rich explosive eruptions in the tropics. Full text in Research Archive Show summary

  Large Plinian volcanic eruptions inject large amounts of atmosphere-relevant gases (e.g. S, Cl, Br) and solid particles into the stratosphere. If the eruption occurs in the tropics, it can have a global impact due to the dispersal through the large scale meridional overturning circulation. Previous modelling studies mainly concentrate on the sulfate aerosol effects on climate and ozone. In contrast, the role of volcanic halogens from tropical eruptions is believed to play an insignificant role for the global atmosphere, based on observations from the recent El Chichon and Pinatubo eruptions. New results regarding the halogen release by paleo Plinian eruptions, as well as recent volcanic plume observations and model simulations facilitate our investigation into what effect the combined chlorine and bromine emissions from large tropical eruptions have on ozone and the atmosphere in general. Here, we present the first study of combined chlorine, bromine from a tropical halogen and sulfur rich volcanic eruption using a state-of-the-art coupled chemistry climate model. A complete halogen and sulfur data set for the last 200ka (Metzner et al, 2013; Kutterolf et al., 2013, 2015), derived by the petrological method from paleo-eruptions of the Central American Volcanic Arc (CAVA), are used to force simulations with WACCM (Whole Atmosphere Community Climate Model). Using the petrological data we simulated 3 forcing scenarios: Sulfur, halogen and combined injections. The goal is to quantify the impact of volcanic halogen and sulfur on the preindustrial atmosphere when the background chlorine levels were low compared to the present day with the main focus on stratospheric ozone. We carried out 5 model simulations of each of the 3 forcing scenarios assuming that 10% of the Cl and Br emitted from the average CAVA eruption is injected into the tropical stratosphere during January. The model response reveals a global impact on the ozone layer affecting, through radiation, atmospheric circulation as well for more than 7 years. Total ozone drops below 220 DU, the present-day ozone hole threshold, in the tropics, Arctic and Antarctica. The increase in biologically active UV caused by the global ozone depletion is found to be more than 80% over much of the northern hemisphere during the first two years post eruption. Given the current decline in anthropogenic chlorine, halogen and sulfur rich explosive tropical eruption will become a major threat for the future ozone layer.

• Fiehn, Alina; Quack, Birgit; Stemmler, Irene & Krüger, Kirstin (2017). What drives the seasonal cycle of stratospheric entrainment of oceanic halogenated VSLS through the Asian monsoon? Full text in Research Archive
• Fiehn, Alina; Hepach, Helmke; Atlas, Elliot L; Quack, Birgit; Tegtmeier, Susann & Krüger, Kirstin (2016). Transport of halogenated very short-lived substances from the Indian Ocean to the stratosphere through the Asian monsoon circulation. Full text in Research Archive
• Fiehn, Alina; Hepach, Helmke; Atlas, Elliot L; Quack, Birgit; Tegtmeier, Susann & Krüger, Kirstin (2015). Transport of halogenated VSLS from the Indian Ocean to the stratosphere through the Asian monsoon circulation. Full text in Research Archive
• Fiehn, Alina; Hepach, Helmke; Atlas, Elliot L; Quack, Birgit; Tegtmeier, Susann & Krüger, Kirstin (2015). Transport of halogenated VSLS from the Indian Ocean to the stratosphere through the Asian monsoon circulation. Full text in Research Archive
• Fiehn, Alina; Hepach, Helmke; Atlas, Elliot L; Quack, Birgit; Tegtmeier, Susann & Krüger, Kirstin (2015). Transport of bromoform from the Indian Ocean to the stratosphere during Asian summer monsoon. Full text in Research Archive Show summary

  Bromoform and other halogenated very short-lived substances (VSLS, atmospheric lifetime less than half a year) are naturally produced in the ocean and emitted to the atmosphere. If transported to the stratosphere, they take part in ozone depletion. The Asian summer monsoon circulation and the deep convection over India may provide an efficient pathway for compounds from the Indian Ocean. We use the Lagrangian transport model FLEXPART with ERA-Interim meteorological fields to discern transport properties during Indian summer monsoon season.

• Zoega, Tomas; Krüger, Kirstin & Storelvmo, Trude (2025). The climate response to high-latitude effusive volcanic eruptions. Universitetet i Oslo. Full text in Research Archive Show summary

  Temaet for denne avhandlingen er klimapåvirkningene som følger av effusive vulkanutbrudd på nordlige høye breddegrader. Slike utbrudd kjennetegnes av aktivitet som ikke er eksplosiv, og gasser som slippes ut ved den slags utbrudd holder seg for det meste i troposfæren. Gjennom utslipp av svoveldioksid og påfølgende dannelse av sulfataerosoler kan effusive vulkanutbrudd påvirke klimaet. Direkte interaksjoner mellom disse vulkanske aerosolene og stråling fører vanligvis til nedkjøling av jorda gjennom økt refleksjon av sollys tilbake ut i verdensrommet. Sulfataerosoler fungerer også som skykondensasjonskjerner og kan derfor påvirke klimaet gjennom vekselvirkning mellom aerosoler og skyer (engelsk: aerosol-cloud interactions, ACI). Dette kompliserer klimapåvirkningen fordi ACI er blant de minst forståtte delene av klimasystemet. Resultatene fra denne avhandlingen presenteres i en rekke av tre vitenskapelige artikler. Den første artikkelen (Artikkel I) er en tilfellestudie av Holuhraun-utbruddet på Island som skjedde i årene 2014 til 2015. Gjennom bevis fra observasjoner og klimamodellering argumenteres det for at dette utbruddet bidro til en økning av overflatetemperaturen i Arktis, særlig over Grønlandshavet, fra september til november 2014, ved at lavtliggende skyer fanget en større del av jordas varmestråling. Den andre artikkelen (Artikkel II) bygger videre på den første. Her er en rekke av Holuhraun-lignende utbrudd i ulike størrelser simulert med startdag i hver av de fire årstidene, nemilg i mars, juni, september og desember. I Arktis viser simuleringene overflateoppvarming om vinteren og mild nedkjøling om sommeren, i begge tilfeller gjennom vekselvirkning mellom vulkanske aerosolene og skyer. Lengre sør, på midlere breddegrader, er overflateresponsen om vinteren stort sett ubetydelig, men om sommeren simuleres en betydelig nedkjøling. Når utbruddene blir større med hensyn til utslipp av svoveldioksid, blir klimapåvirkningen stadig mindre følsom til endringer i utslippsstyrken. Ved utbrudd mellom 20 og 30 ganger større enn Holuhraun-utbruddet i 2014-15 utjevner responsen seg. I den siste artikkelen (Artikkel III) blir klimapåvirkningens avhengighet av klimatilstanden undersøkt. For dette formålet er klimapåvirkningen til effusive vulkanutbrudd simulert i førindustriell tid (året 1850), nåtiden (året 2010) og framtiden (året 2090 i SSP3-7.0 scenarioet). Det viser seg at klimatilstanden har betydelige modulerende effekter på klimapåvirkningen. Overflateoppvarmingen om vinteren i Arktis er sterkere under førindustrielle forhold, sammenlignet med nåtidens og framtidens forhold, på grunn av tynnere skyer i den førindustrielle bakgrunnstilstanden. Derimot blir overflatenedkjølingen om sommeren i Arktis forsterket når klimaet blir varmere, på grunn av mindre havis. Ved europeiske midlere breddegrader finner en betydelig vinterkjøling sted under førindustrielle forhold, sammenlignet med en utydelig temperaturrespons i nåtidens og framtidens klima. Styrken på sommernedkjølingen er sammenlignbar for alle tre klimaforholdene. I Arktis er den sterkeste modulerende faktoren et varmere klima som følge av menneskeskapte klimagassutslipp, med påfølgende endringer i skyegenskaper og redusert havis. Derimot er den sterkeste modulerende faktor på midlere breddegrader bakgrunnstilstanden til aerosoler.

• Fuglestvedt, Herman Fæhn; Krüger, Kirstin; Sigl, Michael; Thordarson, Thorvaldur & Iversen, Frode (2025). The forcing and impacts of Northern high-latitude volcanic eruptions. Universitetet i Oslo. Full text in Research Archive Show summary

  Explosive volcanic eruptions have been the main driver of highfrequency natural climate variability over the last millennia. Eruptions in the high latitudes of the Northern Hemisphere, which are the focus of this thesis, have been far less studied than their tropical counterparts, despite recent research suggesting they can cause more pronounced hemispheric climate effects. High-latitude eruptions are unique for several reasons. The atmosphere in the northern high latitudes is characterised by strong seasonality in atmospheric composition and circulation patterns, along with substantial year-to-year variability. Under these conditions, sulphur and halogen gases released by volcanic eruptions undergo distinct processes that influence their impacts on the atmosphere, climate, and environment, as well as their deposition on the surface. A substantial portion of high-latitude volcanism occurs in Iceland, which is one of the most active volcanic regions on Earth. Among Icelandic eruptions, the 10th-century eruption of Eldgjá is one of the most notable, both for its complexity, with combined effusive and explosive activity over several years, and its magnitude, making it the largest known eruption of its type in the last 2000 years. Despite this, Eldgjá’s climatic and environmental impacts have hardly been investigated. The aim of this thesis is to improve our understanding of the climate forcing and impacts of northern high-latitude volcanic eruptions. To achieve this, large northern high-latitude eruption scenarios are studied using comprehensive aerosol-chemistry-climate modelling to examine relevant processes shaping their forcing and impacts. Initial atmospheric conditions relating to the state of the Arctic polar vortex are shown to play an important role for the dispersion of volcanic volatiles and the formation and evolution of volcanic aerosols, thus affecting the volcanic forcing (Paper I). Dependencies on plume composition, eruption season, and injection height are systematically investigated. This includes the effects of co-injecting volcanic sulphur and halogens, which are prevalent in high-latitude eruptions, on volcanic aerosol evolution and stratospheric ozone (Papers I, III). The simulated forcing and impacts are also compared to those of identical tropical eruptions, showing that northern high-latitude eruptions induce more pronounced responses in the Northern Hemisphere, although shorter in duration (Paper III). Considerable inter-model differences in the simulated forcing of northern high-latitude eruptions are evident when compared to another aerosol-climate model and an idealised volcanic forcing generator (Papers I, III). Furthermore, current methods for reconstructing past volcanic forcing of highlatitude eruptions are refined with new model data, as the range of simulated eruption scenarios provide estimates of scaling factors needed for inferring volcanic stratospheric sulphur injections from deposits in Greenland ice cores. The seasonal dependence of these scaling factors demonstrates that ice-core constraints on the eruption season of past eruptions can be used to refine their reconstructed forcing (Papers I, II). Finally, the Eldgjá eruption is reconstructed using data from Natural archives in Iceland and Greenland, and its climatic and environmental impacts are simulated, demonstrating good agreement with climate proxies (Paper IV). The simulations of Eldgjá highlight compounding impacts that intensify in the northern extratropics during the summers of 939 and 940 CE, as pronounced surface cooling, stratospheric ozone depletion, and increased pollution levels coincide. The simulations also reveal impacts on large-scale precipitation patterns due to hemispheric asymmetry and land-ocean contrast in the surface cooling, as well as prolonged Arctic sea ice growth. The work presented in this thesis contributes to bridging significant gaps in the understanding of high-latitude volcanic eruptions. The improved process understanding and model-based constraints aid in predicting the impacts of future large eruptions or intentional sulphur injections at high latitudes. Furthermore, the work towards refining volcanic forcing reconstructions contributes to improving the accuracy of climate forcing datasets for upcoming model intercomparison projects.

• Auganæs, Sigrid Marie & Krüger, Kirstin (2023). Ozone Above the Tropical Atlantic Ocean. Universitetet i Oslo. Full text in Research Archive Show summary

  Ozon spelar ei avgjerande rolle i atmosfæren både i stratosfæren og troposfæren. Denne avhandlinga undersøker troposfærisk ozon over det tropiske Atlanterhavet ved hjelp av observasjonar, trajektoriar og den norske jordsystemmodellen (NorESM). Forskingsspørsmåla som blir svara på inkluderar tilstadeværet av eit minimum av troposfærisk ozon over det tropiske Atlanterhavet, samanlikning av ozonprofilar mellom skipskampanjar og landbaserte stasjonar, variasjonen i ozon over Atlanterhavet samanlikna med andre havbasseng, og kor godt NorESM modellen representerer observerte ozoneigenskapar. Observasjonar frå SO287 CONNECT skipskampanjen som kryssa det tropiske Atlanterhavet, avslører ingen ozonminimum lik det som førre er observert i det tropiske vestlige Stillehavet. Ozonkonsentrasjonar over det tropiske Atlanterhavet varierte frå 25 til 80 delar per milliard (ppb), med eit gjennomsnitt på 45 ppb gjennom troposfæren. Dei analyserte luftmassane viste karakteristiske eigenskapar frå ulike regionar, som indikerer skogbrannar og stratosfæriske påverknader. Samanlikningar med nærliggande SHADOZ stasjonar bekrefta vellykka prøvetaking av dei same luftmassane av skipskampanjen og Paramaribo SHADOZ stasjonen. Vidare er ozonkonsentrasjonar frå skipskampanjar i med ulike tropiske havbasseng samanklikna, og avdekkjer høgare ozonkonsentrasjonar over det tropiske Atlanterhavet samanlikna med andre tropiske havbasseng. NorESM, inkludert MOZART-TS1 kjemisystemet, fanger opp dei forventa mønstera av overflateozon og wave-one distribusjonar, med nokre avvik. Likevel simulerer modellen den brå økinga av ozon på lågare høgde enn det som er observert, sannsynlegvis på grunn av grov oppløysing i øvre troposfære og stratosfære.

• Fiehn, Alina & Krüger, Kirstin (2017). Transport of very short-lived substances from the Indian Ocean to the stratosphere through the Asian monsoon. Universitetet i Oslo. Full text in Research Archive
• Krüger, Kirstin & Gjermo, Sarah (2017). Transport of very short lived halogenated substances from the tropical East Pacific to the stratosphere and the influence of El Niño 2015/16. Universitetet i Oslo. Full text in Research Archive
• Wærsted, Eivind Grøtting Grøtting & Krüger, Kirstin (2015). Timescales of surface-to-tropopause transport in the tropics, using Flexpart. Universitetet i Oslo. Full text in Research Archive Show summary

  The timescales of transport from the surface to the tropical tropopause layer (TTL) was studied using the Lagrangian transport model Flexpart. The model was driven by the ERA-Interim reanalysis from the European Center for Medium-Range Weather Forecasts (ECMWF). Trajectories were released each month in the period 1. June 2002 - 1. May 2013 at 15 km and 17 km over the whole tropics and simulated 90 days backward in time. The age of air at 15 km and 17 km relative to the last contact with the boundary layer (BL) was computed using a constant BL-height of 1 km above sea level. The aim of the study was to give a detailed description of the tropospheric age of air in the TTL, mainly motivated by the importance of transport timescales for the entry of short-lived compounds to the stratosphere. Several sensitivity studies were carried out. The most important of these were the sensitivity to the use of the convection scheme in Flexpart. In the run without the convection scheme, the median age at 15 km was 17 day longer, and at 17 km 25 days longer, than in the runs using the convection scheme. In particular, the fraction of the air at 17 km younger than 10 days decreased with an order of magnitude, from 11.1 % to 0.9 %. For 30˚S - 30˚N as a whole, the median age was 26 days at 15 km and 50 days at 17 km. A seasonal cycle in the age was found at both altitudes. The seasonal cycle was most pronounced at 17 km, where the median age varied by ∼14 days during the year, being highest in August and lowest in May. At both altitudes, the air was younger near the main convective areas in the tropics, such as the Intertropical Convergence Zone (ITCZ), with less young air approaching the subtropics. The air was particularly young above the tropical western Pacific; the median age there was only 16 days at 15 km and 30 days at 17 km. The air at both 15 km and 17 km was found to originate from the BL above the main convective regions in the tropics. In particular, the West and Central Pacific stood for 40-50 % of the BL-origins. The age decreased over the period, both at 15 km and 17 km. The decrease in the annual median age during 2003-2012 was 2.0 days per decade at 15 km and 9.7 days per decade at 17 km (for 30˚S - 30˚N). Much of this decrease appeared to have taken place around 2009. Interannual variability in the age above the tropical Pacific in December-February (DJF) was found to be related to the El Niño-Southern Oscillation (ENSO). The air was younger above the Pacific in El Niño and older in La Niña. A shift in the BL-origins above the Pacific ocean, eastward in El Niño and westward in La Niña, was also found.

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