Frode Stordal

• Horvath, Peter; Tang, Hui; Halvorsen, Rune; Stordal, Frode; Tallaksen, Lena M.; Berntsen, Terje Koren & Bryn, Anders (2021). Improving the representation of high-latitude vegetation distribution in dynamic global vegetation models. Biogeosciences.  ISSN 1726-4170.  18, s 95- 112 . doi: 10.5194/bg-18-95-2021 Show summary

  Vegetation is an important component in global ecosystems, affecting the physical, hydrological and biogeochemical properties of the land surface. Accordingly, the way vegetation is parameterized strongly influences predictions of future climate by Earth system models. To capture future spatial and temporal changes in vegetation cover and its feedbacks to the climate system, dynamic global vegetation models (DGVMs) are included as important components of land surface models. Variation in the predicted vegetation cover from DGVMs therefore has large impacts on modelled radiative and non-radiative properties, especially over high-latitude regions. DGVMs are mostly evaluated by remotely sensed products and less often by other vegetation products or by in situ field observations. In this study, we evaluate the performance of three methods for spatial representation of present-day vegetation cover with respect to prediction of plant functional type (PFT) profiles – one based upon distribution models (DMs), one that uses a remote sensing (RS) dataset and a DGVM (CLM4.5BGCDV; Community Land Model 4.5 Bio-Geo-Chemical cycles and Dynamical Vegetation). While DGVMs predict PFT profiles based on physiological and ecological processes, a DM relies on statistical correlations between a set of predictors and the modelled target, and the RS dataset is based on classification of spectral reflectance patterns of satellite images. PFT profiles obtained from an independently collected field-based vegetation dataset from Norway were used for the evaluation. We found that RS-based PFT profiles matched the reference dataset best, closely followed by DM, whereas predictions from DGVMs often deviated strongly from the reference. DGVM predictions overestimated the area covered by boreal needleleaf evergreen trees and bare ground at the expense of boreal broadleaf deciduous trees and shrubs. Based on environmental predictors identified by DM as important, three new environmental variables (e.g. minimum temperature in May, snow water equivalent in October and precipitation seasonality) were selected as the threshold for the establishment of these high-latitude PFTs. We performed a series of sensitivity experiments to investigate if these thresholds improve the performance of the DGVM method. Based on our results, we suggest implementation of one of these novel PFT-specific thresholds (i.e. precipitation seasonality) in the DGVM method. The results highlight the potential of using PFT-specific thresholds obtained by DM in development of DGVMs in broader regions. Also, we emphasize the potential of establishing DMs as a reliable method for providing PFT distributions for evaluation of DGVMs alongside RS.

• Guttu, Sigmund; Orsolini, Yvan J.; Stordal, Frode; Limpasuvan, Varavut & Marsh, Daniel R. (2020). WACCM simulations: Decadal winter-to-spring climate impact on middle atmosphere and troposphere from medium energy electron precipitation. Journal of Atmospheric and Solar-Terrestrial Physics.  ISSN 1364-6826.  209 . doi: 10.1016/j.jastp.2020.105382 Full text in Research Archive. Show summary

  Energetic particle precipitation is one of the main processes by which the sun influences atmospheric composition and structure. The polar middle atmosphere is chemically disturbed by the precipitation-induced production of nitric oxides (NOx) and hydrogen oxides (HOx) and the associated ozone (O3) loss, but the importance for the dynamics is still debated. The role of precipitating medium energy electrons (MEEs), which are able to penetrate into the mesosphere, has received increased attention, but has only recently begun to be incorporated in chemistry-climate models. We use the NCAR Whole Atmosphere Community Climate Model (WACCM) to study the climate impact from MEE precipitation by performing two idealized ensemble experiments under pre-industrial conditions, with and without the MEE forcing, over the period of the solar cycle 23 (only full calendar years, 1997–2007). Each experiment includes 20 11-year ensemble members, total 220 years. Our results indicate a strong month-to-month variability in the dynamical response to MEE throughout the winter period. We find a strengthening of the polar vortex in the northern hemisphere during December, but the signal decays rapidly in the following months. The polar vortex strengthening is likely attributable to planetary wave reduction due to increased zonal symmetries in upper stratospheric ozone heating, initially triggered by MEE-induced NOx advected into the sunlit regions. We also find a similar early winter polar vortex strengthening in the southern hemisphere during June. Changes in mean meridional circulation accompany these anomalous wave forcings, leading to dynamically-induced vertical temperature dipoles at high latitudes. The associated weakening of the stratospheric mean meridional circulation results in an upper stratospheric polar ozone deficit in early winter. This polar cap ozone deficit is strongest in the southern hemisphere and contributes to a polar vortex weakening in late winter, in concert with increased planetary wave forcing. In both hemispheres, the stratospheric polar vortex signal seems to migrate downwards into the troposphere and to the surface.

• Hvidsten, Dag; Frafjord, Karl; Gray, Jeremy S.; Henningsson, Anna Jonsson; Jenkins, Andrew; Kristiansen, Bjørn Erik; Lager, Malin; Rognerud, Bjørg; Slåtsve, Arne Martin; Stordal, Frode; Stuen, Snorre & Wilhelmsson, Peter (2020). The distribution limit of the common tick, Ixodes ricinus, and some associated pathogens in north-western Europe. Ticks and Tick-borne Diseases.  ISSN 1877-959X.  11(4) . doi: 10.1016/j.ttbdis.2020.101388 Full text in Research Archive.
• Kumkar, Yogesh; Astrup, Rasmus Andreas; Stordal, Frode & Bright, Ryan M. (2020). Quantifying regional surface energy responses to forest structural change in Nordic Fennoscandia. Journal of Geophysical Research (JGR): Atmospheres.  ISSN 2169-897X.  125(15) . doi: 10.1029/2019JD032092 Show summary

  In a climate model, surface energy and water fluxes of the vegetated ecosystem largely depend on important structural attributes like leaf area index and canopy height. For forests, management can greatly alter these attributes with resulting consequences for the surface albedo, surface roughness, and evapotranspiration. The sensitivity of surface energy and water budgets to alterations in forest structure is relatively unknown in boreal regions, particularly in Nordic Fennoscandia (Norway, Sweden, and Finland), where the forest management footprint is large. Here we perform offline simulations to quantify the sensitivity of surface heat and moisture fluxes to changes in forest composition and structure across daily, seasonal, and annual time scales. For the region on average, it is found that broadleaved deciduous forests cool the surface by 0.16 K annually and 0.3 K in the growing season owed to higher year‐round albedo and lower Bowen ratio, yet in some locations the local cooling can be as much as 2.4 K and 3.0 K, respectively. Moreover, fully developed forests cool the surface by 0.04 K annually in our domain owed to higher evapotranspiration, reaching up to 0.4 K locally in some locations, whereas undeveloped forests warm annually by 0.14 K owed to much lower evapotranspiration reaching up to 0.8 K for some locations. If regional forests are ever to be managed for the local climate regulation services that they provide, our results are an important first step illuminating the potential adverse impacts or benefits across space and time.

• Myers-Smith, Isla H.; Kerby, Jeffrey T.; Phoenix, Gareth K.; Bjerke, Jarle W.; Epstein, Howard E.; Assmann, Jakob J.; John, Christian; Andreu-Hayles, Laia; Angers-Blondin, Sandra; Beck, Pieter S.A.; Berner, Logan T.; Bhatt, Uma S.; Björkman, Anne D.; Blok, Daan; Bryn, Anders; Christiansen, Casper Tai; Cornelissen, J. Hans C.; Cunliffe, Andrew M.; Elmendorf, Sarah C.; Forbes, Bruce C.; Goetz, Scott J.; Hollister, Robert D.; de Jong, Rogier; Loranty, Michael M.; Macias-Fauria, Marc; Maseyk, Kadmiel; Normand, Signe; Olofsson, Johan; Parker, Thomas C.; Parmentier, Frans-Jan W.; Post, Eric; Schaepman-Strub, Gabriela; Stordal, Frode; Sullivan, Patrick F.; Thomas, Haydn J.D.; Tømmervik, Hans; Treharne, Rachael; Tweedie, Craig E.; Walker, Donald A.; Wilmking, Martin & Wipf, Sonja (2020). Complexity revealed in the greening of the Arctic. Nature Climate Change.  ISSN 1758-678X.  10(2), s 106- 117 . doi: 10.1038/s41558-019-0688-1 Full text in Research Archive. Show summary

  As the Arctic warms, vegetation is responding, and satellite measures indicate widespread greening at high latitudes. This ‘greening of the Arctic’ is among the world’s most important large-scale ecological responses to global climate change. However, a consensus is emerging that the underlying causes and future dynamics of so-called Arctic greening and browning trends are more complex, variable and inherently scale-dependent than previously thought. Here we summarize the complexities of observing and interpreting high-latitude greening to identify priorities for future research. Incorporating satellite and proximal remote sensing with in-situ data, while accounting for uncertainties and scale issues, will advance the study of past, present and future Arctic vegetation change.

• Vedeld, Trond; Hofstad, Hege; Mathur, Mihir; Büker, Patrick & Stordal, Frode (2020). Reaching out? Governing weather and climate services (WCS) for farmers. Environmental Science and Policy.  ISSN 1462-9011.  104, s 208- 216 . doi: 10.1016/j.envsci.2019.11.010 Show summary

  High-quality weather and climate services (WCS) can be critical for communicating knowledge about current and future weather and climate risks for adaptation and disaster risk management in the agricultural sector. This paper investigates the structure and performance of weather and climate services for farmers from a governance perspective. Empirically the paper compares the institutional design and operations of agro-meteorological services in Maharashtra/India and Norway through a ‘most different case study’ approach. The two cases were selected to represent great diversity in location, scale and institutional design. A governance approach based on semi-direct interviews and policy and institutional analysis was combined with local survey data of farmers’ perceptions and use of the services. Despite the fact that the context for the two agromet advisory services was very different from a climate-weather, eco-agriculture, and socio-institutional angle, the analysis reveals great similarities in the services structures and critical governance challenges. In both countries the agromet services communicated knowledge that was largely perceived not to be well tailored to farmers’ needs for decisions in specific crops- and farm operations, spatially too coarse to address local issues, and, often unreliable or inaccurate in terms of the quality of data. Farmers did, however, respond positively to specific and locally relevant information on e.g., warnings about high rainfall and spread of pests. Observing such similarities across very diverse contexts enhances the generalization potential, precisely because they evolved under very different circumstances. Similar observations find support in the wider WCS literature. Based on the empirical findings, we propose a more deliberate approach to institutional design of WCS in order to enhance governance performance and co-creation of the services at local, district and national scales. It is suggested that greater participation of farmers and agricultural extension agents in the co-creation of these services is a necessary means of improving the services, supported by the WCS literature. However, we insist that greater participation is only likely to materialize if the deficiencies in institutional design and knowledge quality and relevance are addressed to greater extent than done today. The comparison between the two services shows that Norway can learn from India that a more ambitious scope and multiple forms of communication, including the use of social media/ WhatsApp groups, can facilitate greater awareness and interest among farmers in multi-purpose agromet services for multi-way communication. India can learn from Norway that a more integrated and decentralized institutional design can strengthen the network attributes of the services, foster co-creation, and improve participation of both poor and large-scale farmers and extension agents.

• Bhattarai, Bikas Chandra; Burkhart, John; Stordal, Frode & Xu, Chong-Yu (2019). Aerosol Optical Depth Over the Nepalese Cryosphere Derived From an Empirical Model. Frontiers in Earth Science.  ISSN 2296-6463.  7 . doi: 10.3389/feart.2019.00178 Full text in Research Archive.
• Horvath, Peter; Halvorsen, Rune; Stordal, Frode; Tallaksen, Lena Merete; Tang, Hui & Bryn, Anders (2019). Distribution modelling of vegetation types based on area frame survey data. Applied Vegetation Science.  ISSN 1402-2001.  22(4), s 547- 560 . doi: 10.1111/avsc.12451 Show summary

  Aim: Many countries lack informative, high‐resolution, wall‐to‐wall vegetation or land cover maps. Such maps are useful for land use and nature management, and for input to regional climate and hydrological models. Land cover maps based on remote sensing data typically lack the required ecological information, whereas traditional field‐based mapping is too expensive to be carried out over large areas. In this study, we therefore explore the extent to which distribution modelling (DM) methods are useful for predicting the current distribution of vegetation types (VT) on a national scale. Location: Mainland Norway, covering ca. 324,000 km2. Methods: We used presence/absence data for 31 different VTs, mapped wall‐to‐wall in an area frame survey with 1081 rectangular plots of 0.9 km2. Distribution models for each VT were obtained by logistic generalised linear modelling, using stepwise forward selection with an F‐ratio test. A total of 116 explanatory variables, recorded in 100 m × 100 m grid cells, were used. The 31 models were evaluated by applying the AUC criterion to an independent evaluation dataset. Results: Twenty‐one of the 31 models had AUC values higher than 0.8. The highest AUC value (0.989) was obtained for Poor/rich broadleaf deciduous forest, whereas the lowest AUC (0.671) was obtained for Lichen and heather spruce forest. Overall, we found that rare VTs are predicted better than common ones, and coastal VTs are predicted better than inland ones. Conclusions: Our study establishes DM as a viable tool for spatial prediction of aggregated species‐based entities such as VTs on a regional scale and at a fine (100 m) spatial resolution, provided relevant predictor variables are available. We discuss the potential uses of distribution models in utilizing large‐scale international vegetation surveys. We also argue that predictions from such models may improve parameterisation of vegetation distribution in earth system models.

• Justino, Flavio; Kucharski, Fred; Lindemann, Douglas; Wilson, Aaron & Stordal, Frode (2019). A modified seasonal cycle during MIS31 super-interglacial favors stronger interannual ENSO and monsoon variability. Climate of the Past.  ISSN 1814-9324.  15(2), s 735- 749 . doi: 10.5194/cp-15-735-2019 Full text in Research Archive.
• Pall, Pardeep; Tallaksen, Lena M. & Stordal, Frode (2019). A Climatology of Rain-on-Snow Events for Norway. Journal of Climate.  ISSN 0894-8755.  32(20), s 6995- 7016 . doi: 10.1175/JCLI-D-18-0529.1 Full text in Research Archive.
• Benestad, Rasmus; van Oort, Bob; Justino, Flavio; Stordal, Frode; Parding, Kajsa; Mezghani, Abdelkader; Erlandsen, Helene B.; Sillmann, Jana & Pereira-Flores, Milton E (2018). Downscaling probability of long heatwaves based on seasonal mean daily maximum temperatures. Advances in Statistical Climatology, Meteorology and Oceanography (ASCMO).  ISSN 2364-3579.  4, s 37- 52 . doi: 10.5194/ascmo-4-37-2018 Full text in Research Archive. Show summary

  A methodology for estimating and downscaling the probability associated with the duration of heatwaves is presented and applied as a case study for Indian wheat crops. These probability estimates make use of empirical-statistical downscaling and statistical modelling of probability of occurrence and streak length statistics, and we present projections based on large multi-model ensembles of global climate models from the Coupled Model Intercomparison Project Phase 5 and three different emissions scenarios: Representative Concentration Pathways (RCPs) 2.6, 4.5, and 8.5. Our objective was to estimate the probabilities for heatwaves with more than 5 consecutive days with daily maximum temperature above 35 ∘C, which represent a condition that limits wheat yields. Such heatwaves are already quite frequent under current climate conditions, and downscaled estimates of the probability of occurrence in 2010 is in the range of 20 %–84 % depending on the location. For the year 2100, the high-emission scenario RCP8.5 suggests more frequent occurrences, with a probability in the range of 36 %–88 %. Our results also point to increased probabilities for a hot day to turn into a heatwave lasting more than 5 days, from roughly 8 %–20 % at present to 9 %–23 % in 2100 assuming future emissions according to the RCP8.5 scenario; however, these estimates were to a greater extent subject to systematic biases. We also demonstrate a downscaling methodology based on principal component analysis that can produce reasonable results even when the data are sparse with variable quality.

• Dyrrdal, Anita Verpe; Stordal, Frode & Lussana, Cristian (2018). Evaluation of summer precipitation from EURO-CORDEX fine-scale RCM simulations over Norway. International Journal of Climatology.  ISSN 0899-8418.  38(4), s 1661- 1677 . doi: 10.1002/joc.5287 Show summary

  http://onlinelibrary.wiley.com/doi/10.1002/joc.5287/full Regional climate models represent a valuable tool in climate impact analyses. Their ability to accurately estimate current and future climate conditions is increasingly important. In Norway precipitation is of special interest. Heavy precipitation, particularly over short durations, is responsible for enormous damages to infrastructure such as roads and railways, hence information on a fine spatial and temporal scale is crucial. We evaluate the ability of seven regional climate model simulations of 0.11° resolution from the CORDEX ensemble in reproducing 3-h and 24-h accumulated summer precipitation characteristics in Norway. The two-step evaluation includes comparison of modelled precipitation to gridded observation-based datasets and to station measurements in terms of the following indices: summer maxima, summer wet event frequency, and total summer precipitation. We find a general overestimation by the models for all indices, with only few exceptions. Country-wide spatial averages show, however, that simulated summer maxima are mainly within the uncertainty interval of the gridded reference dataset. This might also be true for summer wet event frequency, although the comparison to station measurements indicates that the positive bias is significant. We find the largest deviation between models in the evaluation of summer totals. The spatial distribution of the different precipitation indices is fairly well simulated, although the precipitation gradients evident in observation-based datasets appear weak in the models. We believe the high spatial resolution improves the simulations of extreme precipitation in Norway, especially in areas of orographic enhancement.

• Orsolini, Yvan; Smith-Johnsen, Christine; Marsh, Daniel R.; Stordal, Frode; Rodger, Craig J.; Verronen, Pekka T. & Clilverd, Mark A. (2018). Mesospheric nitric acid enhancements during energetic electron precipitation events simulated by WACCM‐D. Journal of Geophysical Research (JGR): Atmospheres.  ISSN 2169-897X.  123(13), s 6984- 6998 . doi: 10.1029/2017JD028211 Full text in Research Archive.
• Smith-Johnsen, Christine; Marsh, Daniel R.; Orsolini, Yvan; Tyssøy, Hilde Nesse; Hendrickx, Koen; Sandanger, Marit Irene J.; Ødegaard, Linn-Kristine Glesnes & Stordal, Frode (2018). Nitric oxide response to the April 2010 electron precipitation event: Using WACCM and WACCM-D with and without medium-energy electrons. Journal of Geophysical Research (JGR): Space Physics.  ISSN 2169-9380.  123(6), s 5232- 5245 . doi: 10.1029/2018JA025418 Full text in Research Archive. Show summary

  Energetic electrons from the magnetosphere deposit their energy in the atmosphere and lead to production of nitric oxide (NO) in the mesosphere and lower thermosphere. We study the atmospheric NO response to a geomagnetic storm in April 2010 with WACCM (Whole Atmosphere Community Climate Model). Modeled NO is compared to observations by Solar Occultation For Ice Experiment/Aeronomy of Ice in the Mesosphere at 72–82°S latitudes. We investigate the modeled NOs sensitivity to changes in energy and chemistry. The electron energy model input is either a parameterization of auroral electrons or a full range energy spectrum (1–750 keV) from National Oceanic and Atmospheric Administration/Polar Orbiting Environmental Satellites and European Organisation for the Exploitation of Meteorological Satellites/Meteorological Operational satellites. To study the importance of ion chemistry for the production of NO, WACCM‐D, which has more complex ion chemistry, is used. Both standard WACCM and WACCM‐D underestimate the storm time NO increase in the main production region (90–110 km), using both electron energy inputs. At and below 80 km, including medium‐energy electrons (>30 keV) is important both for NO directly produced at this altitude region and for NO transported from other regions (indirect effect). By using WACCM‐D the direct NO production is improved, while the indirect effects on NO suffer from the downward propagating deficiency above. In conclusion, both a full range energy spectrum and ion chemistry is needed throughout the mesosphere and lower thermosphere region to increase the direct and indirect contribution from electrons on NO.

• Smith-Johnsen, Christine; Orsolini, Yvan; Stordal, Frode; Limpasuvan, Varavut & Pérot, Kristell (2018). Nighttime mesospheric ozone enhancements during the 2002 southern hemispheric major stratospheric warming. Journal of Atmospheric and Solar-Terrestrial Physics.  ISSN 1364-6826.  168, s 100- 108 . doi: 10.1016/j.jastp.2017.12.018 Full text in Research Archive. Show summary

  Sudden Stratospheric Warmings (SSW) affect the chemistry and dynamics of the middle atmosphere. Major warmings occur roughly every second winter in the Northern Hemisphere (NH), but has only been observed once in the Southern Hemisphere (SH), during the Antarctic winter of 2002. Observations by the Global Ozone Monitoring by Occultation of Stars (GOMOS, an instrument on board Envisat) during this rare event, show a 40% increase of ozone in the nighttime secondary ozone layer at subpolar latitudes compared to non-SSW years. This study investigates the cause of the mesospheric nighttime ozone increase, using the National Center for Atmospheric Research (NCAR) Whole Atmosphere Community Climate Model with specified dynamics (SD-WACCM). The 2002 SH winter was characterized by several reductions of the strength of the polar night jet in the upper stratosphere before the jet reversed completely, marking the onset of the major SSW. At the time of these wind reductions, corresponding episodic increases can be seen in the modelled nighttime secondary ozone layer. This ozone increase is attributed largely to enhanced upwelling and the associated cooling of the altitude region in conjunction with the wind reversal. This is in correspondence to similar studies of SSW induced ozone enhancements in NH. But unlike its NH counterpart, the SH secondary ozone layer appeared to be impacted less by episodic variations in atomic hydrogen. Seasonally decreasing atomic hydrogen plays however a larger role in SH compared to NH.

• Diallo, Ismaïla; Giorgi, Filippo & Stordal, Frode (2017). Influence of Lake Malawi on regional climate from a double-nested regional climate model experiment. Climate Dynamics.  ISSN 0930-7575.  s 1- 15 . doi: 10.1007/s00382-017-3811-x
• Justino, Flavio; Lindemann, Douglas; Kucharski, Fred; Wilson, Aaron; Bromwich, David & Stordal, Frode (2017). Oceanic response to changes in the WAIS and astronomical forcing during the MIS31 superinterglacial. Climate of the Past.  ISSN 1814-9324.  13(9), s 1081- 1095 . doi: 10.5194/cp-13-1081-2017 Full text in Research Archive.
• Rydsaa, Johanne Hope; Stordal, Frode; Bryn, Anders & Tallaksen, Lena M. (2017). Effects of shrub and tree cover increase on the near-surface atmosphere in northern Fennoscandia. Biogeosciences.  ISSN 1726-4170.  14(18), s 4209- 4227 . doi: 10.5194/bg-14-4209-2017 Full text in Research Archive.
• Smith-Johnsen, Christine; Tyssøy, Hilde Nesse; Hendrickx, Koen; Orsolini, Yvan; Kishore Kumar, Grandhi; Ødegaard, Linn-Kristine Glesnes; Sandanger, Marit Irene J.; Stordal, Frode & Megner, Linda (2017). Direct and indirect electron precipitation effect on nitric oxide in the polar middle atmosphere, using a full-range energy spectrum. Journal of Geophysical Research (JGR): Space Physics.  ISSN 2169-9380.  122(8), s 8679- 8693 . doi: 10.1002/2017JA024364 Full text in Research Archive.
• Stordal, Frode; Svensen, Henrik; Aarnes, Ingrid & Roscher, Marco (2017). Global temperature response to century-scale degassing from the Siberian Traps Large igneous province. Palaeogeography, Palaeoclimatology, Palaeoecology.  ISSN 0031-0182.  471, s 96- 107 . doi: 10.1016/j.palaeo.2017.01.045 Show summary

  The Siberian Traps Large igneous province was a key player in the end-Permian extinction and climatic change due to degassing from lavas and heated sedimentary rocks. Although the specific degassing scenarios from the province are debated, this implies that gas release on a timescale tuned to the cooling of lava flows and subvolcanic intrusions (i.e. decades to centuries) must have been sufficient to affect the atmospheric chemistry. Here we test this assumption by using simple box model calculations to constrain century-scale degassing of CO2 and CH4 from high-end volumes of individual lava flows and sills from the Siberian Traps. The model includes gas fluxes of CH4 and CO2, their atmospheric lifetimes and radiative forcing, as well as the climate sensitivity in a global average climate system calibrated to end-Permian time. The fluxes are estimated based on lava degassing and contact aureole volumes and devolatilization during the first 100 years following emplacement. We test the sensitivity to extreme emissions of up to 25 GtC/yr, CH4 fractions from 0 to 100%, wide ranges of climate sensitivities (1.5–6.0 °C for CO2 doubling), pre-event concentrations, and atmospheric lifetimes. We find that the global annual mean temperature perturbation is 7.0 °C in our baseline case using a 10 GtC/yr emission and a 60% CH4 fraction, assuming 4.5 °C as the climate sensitivity. Even for low emission scenarios (0.7–1.2 GtC/yr), the temperature response is ~ 1.5 °C. We conclude that sporadic individual large-scale volcanic events in Large igneous provinces have the potential to cause a strong global warming on very short timescales. In addition to the emission strength, the CH4 fraction and the climate sensitivity have the strongest impact on the century-scale temperature perturbation.

• Dyrrdal, Anita Verpe; Skaugen, Thomas; Stordal, Frode & Førland, Eirik (2016). Estimating extreme areal precipitation in Norway from a gridded dataset. Hydrological Sciences Journal.  ISSN 0262-6667.  61(3), s 483- 494 . doi: 10.1080/02626667.2014.947289
• Laken, Benjamin Alexander & Stordal, Frode (2016). Are there statistical links between the direction of European weather systems and ENSO, the solar cycle or stratospheric aerosols?. Royal Society Open Science.  ISSN 2054-5703.  3(2) . doi: 10.1098/rsos.150320
• Mtongori, Habiba Ismail; Stordal, Frode & Benestad, Rasmus (2016). Evaluation of empirical statistical downscaling models' skill in predicting Tanzanian rainfall and their application in providing future downscaled scenarios. Journal of Climate.  ISSN 0894-8755.  29(9), s 3231- 3252 . doi: 10.1175/JCLI-D-15-0061.1
• Pereira-Flores, Milton E; Justino, Flavio; Ruiz-Vera, Ursula M; Stordal, Frode; Martins Melo, Anderson A & Rodrigues, Rafael de avila (2016). Response of soybean yield components and allocation of dry matter to increased temperature and CO2 concentration. Australian Journal of Crop Science.  ISSN 1835-2693.  10(6), s 808- 818 . doi: 10.21475/ajcs.2016.10.06.p7310
• Rydsaa, Johanne Hope; Stordal, Frode; Gerosa, Giacomo; Finco, Angelo & Hodnebrog, Øivind (2016). Evaluating stomatal ozone fluxes in WRF-Chem: Comparing ozone uptake in Mediterranean ecosystems. Atmospheric Environment.  ISSN 1352-2310.  143, s 237- 248 . doi: 10.1016/j.atmosenv.2016.08.057 Show summary

  The development of modelling tools for estimating stomatal uptake of surface ozone in vegetation is important for the assessment of potential damage induced due to both current and future near surface ozone concentrations. In this study, we investigate the skill in estimating ozone uptake in plants by the Weather Research and Forecasting model coupled with chemistry (WRF-Chem) V3.6.1, with the Wesely dry deposition scheme. To validate the stomatal uptake of ozone, the model simulations were compared with field measurements of three types of Mediterranean vegetation, over seven different periods representing various meteorological conditions. Some systematic biases in modelled ozone fluxes are revealed; the lack of an explicit and time varying dependency on plants’ water availability results in overestimated daytime ozone stomatal fluxes particularly in dry periods. The optimal temperature in the temperature response function is likely too low for the woody species tested here. Also, too low nighttime stomatal conductance leads to underestimation of ozone uptake during night. We demonstrate that modelled stomatal ozone flux is improved by accounting for vapor pressure deficit in the ambient air. Based on the results of the overall comparison to measured fluxes, we propose that additional improvements to the stomatal conductance parameterization should be implemented before applying the modelling system for estimating ozone doses and potential damage to vegetation.

• 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), s 401- 412 . doi: 10.1007/s10584-016-1648-7
• Aas, Kjetil Schanke; Berntsen, Terje Koren; Boike, Julia; Etzelmuller, Bernd; Kristjansson, Jon Egill; Maturilli, Marion; Schuler, Thomas; Stordal, Frode & Westermann, Sebastian (2015). A comparison between simulated and observed surface energy balance at the Svalbard Archipelago. Journal of Applied Meteorology and Climatology.  ISSN 1558-8424.  54(5), s 1102- 1119 . doi: 10.1175/JAMC-D-14-0080.1
• Diallo, Ismaïla; Giorgi, Filippo; Sukumaran, Sandeep; Stordal, Frode & Giuliani, Graziano (2015). Evaluation of RegCM4 driven by CAM4 over Southern Africa: mean climatology, interannual variability and daily extremes of wet season temperature and precipitation. Theoretical and Applied Climatology.  ISSN 0177-798X.  121(3), s 749- 766 . doi: 10.1007/s00704-014-1260-6
• Dyrrdal, Anita Verpe; Lenkoski, Alex; Thorarinsdottir, Thordis Linda & Stordal, Frode (2015). Bayesian hierarchical modeling of extreme hourly precipitation in Norway. Environmetrics.  ISSN 1180-4009.  26(2), s 89- 106 . doi: 10.1002/env.2301 Show summary

  Spatial maps of extreme precipitation are a critical component of flood estimation in hydrological modeling, as well as in the planning and design of important infrastructure. This is particularly relevant in countries, such as Norway, that have a high density of hydrological power generating facilities and are exposed to significant risk of infrastructure damage due to flooding. In this work, we estimate a spatially coherent map of the distribution of extreme hourly precipitation in Norway, in terms of return levels, by linking generalized extreme value (GEV) distributions with latent Gaussian fields in a Bayesian hierarchical model. Generalized linear models on the parameters of the GEV distribution are able to incorporate location-specific geographic and meteorological information and thereby accommodate these effects on extreme precipitation. Our model incorporates a Bayesian model averaging component that directly assesses model uncertainty in the effect of the proposed covariates. Gaussian fields on the GEV parameters capture additional unexplained spatial heterogeneity and overcome the sparse grid on which observations are collected. Our framework is able to appropriately characterize both the spatial variability of the distribution of extreme hourly precipitation in Norway and the associated uncertainty in these estimates.

• Hvidsten, Dag; Stordal, Frode; Lager, Malin; Rognerud, Bjørg; Kristiansen, Bjørn Erik; Matussek, Andreas; Gray, Jeremy & Stuen, Snorre (2015). Borrelia burgdorferi sensu lato-infected Ixodes ricinus collected from vegetation near the Arctic Circle. Ticks and Tick-borne Diseases.  ISSN 1877-959X.  6(6), s 768- 773 . doi: 10.1016/j.ttbdis.2015.07.002 Full text in Research Archive.
• Justino, F.; Silva, A. S.; Pereira, M. P.; Stordal, Frode; Lindemann, D & Kucharski, F. (2015). The large-scale climate in response to the retreat of the West Antarctic ice sheet. Journal of Climate.  ISSN 0894-8755.  28(2), s 637- 650 . doi: 10.1175/JCLI-D-14-00284.1
• Li, Lu; Diallo, Ismaïla; Xu, Chong-Yu & Stordal, Frode (2015). Hydrological projections under climate change in the near future by RegCM4 in Southern Africa using a large-scale hydrological model. Journal of Hydrology.  ISSN 0022-1694.  528, s 1- 16 . doi: 10.1016/j.jhydrol.2015.05.028
• Lindholm, Markus; Hessen, Dag Olav; Færøvig, Per-Johan; Rognerud, Bjørg; Andersen, Tom & Stordal, Frode (2015). Is distribution of cold stenotherms constrained by temperature? The case of the Arctic fairy shrimp (Branchinecta paludosa O.F. Müller 1788). Journal of Thermal Biology.  ISSN 0306-4565.  53, s 46- 52 . doi: 10.1016/j.jtherbio.2015.08.005
• Rydsaa, Johanne Hope; Stordal, Frode & Tallaksen, Lena M. (2015). Sensitivity of the regional European boreal climate to changes in surface properties resulting from structural vegetation perturbations. Biogeosciences.  ISSN 1726-4170.  12(10), s 3071- 3087 . doi: 10.5194/bg-12-3071-2015
• Isaksen, Ivar S A; Berntsen, Terje Koren; Dalsøren, Stig Bjørløw; Eleftheratos, K.; Orsolini, Yvan; Rognerud, Bjørg; Stordal, Frode; Søvde, Ole Amund; Zerefos, C & Holmes, Chris D. (2014). Atmospheric Ozone and Methane in a Changing Climate. Atmosphere.  ISSN 2073-4433.  5(3), s 518- 535 . doi: 10.3390/atmos5030518 Full text in Research Archive. Show summary

  Ozone and methane are chemically active climate-forcing agents affected by climate–chemistry interactions in the atmosphere. Key chemical reactions and processes affecting ozone and methane are presented. It is shown that climate-chemistry interactions have a significant impact on the two compounds. Ozone, which is a secondary compound in the atmosphere, produced and broken down mainly in the troposphere and stratosphre through chemical reactions involving atomic oxygen (O), NOx compounds (NO, NO2), CO, hydrogen radicals (OH, HO2), volatile organic compounds (VOC) and chlorine (Cl, ClO) and bromine (Br, BrO). Ozone is broken down through changes in the atmospheric distribution of the afore mentioned compounds. Methane is a primary compound emitted from different sources (wetlands, rice production, livestock, mining, oil and gas production and landfills).Methane is broken down by the hydroxyl radical (OH). OH is significantly affected by methane emissions, defined by the feedback factor, currently estimated to be in the range 1.3 to 1.5, and increasing with increasing methane emission. Ozone and methane changes are affected by NOx emissions. While ozone in general increase with increases in NOx emission, methane is reduced, due to increases in OH. Several processes where current and future changes have implications for climate-chemistry interactions are identified. It is also shown that climatic changes through dynamic processes could have significant impact on the atmospheric chemical distribution of ozone and methane, as we can see through the impact of Quasi Biennial Oscillation (QBO). Modeling studies indicate that increases in ozone could be more pronounced toward the end of this century. Thawing permafrost could lead to important positive feedbacks in the climate system. Large amounts of organic material are stored in the upper layers of the permafrost in the yedoma deposits in Siberia, where 2 to 5% of the deposits could be organic material. During thawing of permafrost, parts of the organic material that is deposited could be converted to methane. Furthermore, methane stored in deposits under shallow waters in the Arctic have the potential to be released in a future warmer climate with enhanced climate impact on methane, ozone and stratospheric water vapor. Studies performed by several groups show that the transport sectors have the potential for significant impacts on climate-chemistry interactions. There are large uncertainties connected to ozone and methane changes from the transport sector, and to methane release and climate impact during permafrost thawing.

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• Bryn, Anders; Dalen, Thea Grobstok; Finne, Eirik Aasmo; Heiberg, Hanne; Nilsen, Irene Brox; Parmentier, Frans-Jan W.; Snekkenes, Christine; Stordal, Frode; Aas, Kjetil Schanke; Althuizen, Inge; Berntsen, Terje Koren; Bjerke, Jarle W.; Bright, Ryan M.; Dyrrdal, Anita Verpe; Geange, Sonya Rita; Pirk, Norbert; Puschmann, Oskar; Tang, Hui; Torma, Michal; Vollsnes, Ane Victoria; Westermann, Sebastian & Yilmaz, Yeliz (2020). Natur i endring.
• Bryn, Anders; Hessen, Dag Olav & Stordal, Frode (2020). Før det bikker over. Klassekampen.  ISSN 0805-3839.  s 18- 19
• Falk, Stefanie; Vollsnes, Ane Victoria; Stordal, Frode; Eriksen, Aud Else Berglen & Berntsen, Terje Koren (2020). Surface Ozone in Northern Scandinavia and Implications on Local Vegetation - A Case Study. Show summary

  The Arctic biosphere is subject to comprehensive changes induced by climate change. The highly specialized subartic vegetation will be challenged by both, changing environmental conditions as well as further interference through human activity. Permission of exploitation of natural resources in the Artic is likely to increase the levels of air pollutants which are precursors to ozone. n the course of our project (OzoNorClim: The Double Punch), we had an ozone monitor installed at the Norwegian Institute for Bioeconomic Research (NIBIO) Svanhovd Research Station operated by the Norwegian Institute for Air Research (NILU). In 2018, a long-lasting heatwave accompanied by extensive forest fires across Europe and Scandinavia enhanced surface ozone concentrations by about 2 ppt above the climatological mean in Northern Scandinavia. Ozone sensitive glover species in the ozone garden at Svanhovd showed clear signs of ozone damage in 2018 but not in 2019. We study these two years as example for probable future scenarios in which both heat stress and ozone stress affect vegetation negatively. We look at the corresponding surface ozone concentrations, accumulated ozone dose, and implications on natural and semi-natural vegetation especially in the Pasvik valley in Northern Norway, put these in a larger regional context, and give an outlook on further modelling work.

• Guttu, Sigmund; Orsolini, Yvan J.; Stordal, Frode; Limpasuvan, Varavut & Marsh, Daniel R. (2020). Impact of Medium-Energy Electron Precipitation on Ozone and Middle Atmosphere Dynamics in WACCM Simulations.
• Guttu, Sigmund; Orsolini, Yvan; Stordal, Frode; Otterå, Odd Helge; Toniazzo, Thomas & Verronen, Pekka T. (2020). Effects of the 11-year Solar Cycle including Medium-Energy Electron Precipitation in WACCM decadal climate predictions.
• Lieungh, Eva; Bryn, Anders; Stordal, Frode; Bjerke, Jarle W.; Tonjer, Lea-Rebekka & Bright, Ryan M. (2020). Norske fjell gror igjen i et varmere klima. Aftenposten (morgenutg. : trykt utg.).  ISSN 0804-3116.  s 20- 21
• Stordal, Frode (2020). Dissolved organic matter: From atmosphere to rivers and lakes.
• Vollsnes, Ane Victoria; Falk, Stefanie; Eriksen, Aud Berglen; Kapperud, Åshild Fandango; Kauserud, Håvard; Stordal, Frode & Berntsen, Terje Koren (2020). Responses to experimental ozone exposure in some native plant species from Northern Scandinavia.
• Vollsnes, Ane Victoria; Falk, Stefanie; Eriksen, Aud Else Berglen; Stordal, Frode; Kauserud, Håvard; Berntsen, Terje Koren; Emberson, Lisa D.; O’Neill, Connie & Lombardozzi, Danica (2020). The double punch: ozone and climate stresses on vegetation.
• Yilmaz, Yeliz A.; Aalstad, Kristoffer; Filhol, Simon Vincent P; Stordal, Frode & Tallaksen, Lena M. (2020). Fennoscandian snow cover phenology from MODIS, CLM5, and climate reanalyses.
• Yilmaz, Yeliz A.; Aalstad, Kristoffer; Filhol, Simon Vincent P; Stordal, Frode & Tallaksen, Lena M. (2020). Scandinavian snow cover phenology from MODIS, CLM, and reanalyses.
• Yilmaz, Yeliz A.; Aalstad, Kristoffer; Filhol, Simon Vincent P; Stordal, Frode & Tallaksen, Lena M. (2020). The Representation of the Fennoscandian Snow Cover Phenology in Reanalyses and CLM5 during the MODIS-era. Show summary

  Snow plays an important role in cold regions through its effect on the terrestrial exchange of energy, water, and carbon. Accurately simulating snow processes is therefore important in capturing various climate feedbacks in Earth system models. The representation of the subgrid heterogeneity of snow properties (e.g. coverage, depth, density, albedo) are, in addition to accumulation and snowmelt, major sources of uncertainty in the snow modules of land surface schemes. Using multiple data sources is essential to address these uncertainties and to evaluate overall model performance. Unlike in-situ observations, satellite remote sensing products provide unique representative information at the scale of Earth system models. The Moderate Resolution Imaging Spectroradiometer (MODIS) sensor onboard the Aqua and Terra satellites provide a continuous long-term climate record for the last two decades. In this study, two daily snow cover data sets from MODIS (MOD10A1 and MYD10A1) were used to retrieve fractional snow-covered area (fSCA) and several snow cover metrics (e.g. snow cover duration, first and last day of snow) over Fennoscandia for the 2001-2020 water years. We use these retrievals to evaluate the fSCA outputs from multiple reanalyses (ERA5-Land, ERA5, and MERRA-2) and the latest version of the Community Land Model (CLM5) which is the land component of the Community Earth System Model (CESM) and the Norwegian Earth System Model (NorESM). In order to test the accuracy of the MODIS data, we employed Sentinel-2 and Landsat 8 satellite retrievals as well as local‐scale measurements around the Finse Eco-Hydrological Observatory (Finse EcHO), a low-alpine site in central Norway. Lastly, we compared the trends in snow cover metrics with terrestrial water storage anomalies obtained from the Gravity Recovery and Climate Experiment (GRACE) to better understand the regional water cycle dynamics over this region. This study provides a useful starting point for integrating Earth observations into Earth system modeling in cold regions to help identify and constrain sources of uncertainty. Acknowledgement : This study is conducted under the LATICE strategic research initiative funded by the Faculty of Mathematics and Natural Sciences at the University of Oslo, and the EMERALD (project #294948) funded by the Research Council of Norway.

• Yilmaz, Yeliz; Tallaksen, Lena M. & Stordal, Frode (2020). Hydroclimatological evaluation of CLM5 simulations using multiple data sources for land-atmosphere interaction studies over Scandinavia. Show summary

  Arctic amplification leads to rapid changes in the terrestrial water and energy balances at high northern latitudes. Advances in Earth System Models (ESMs) is improving our understanding of the underlying feedback mechanisms leading to these changes. The representation of the land surface in ESMs is essential to simulate and understand changes at the global and regional scales. The latest version of the land component of the Norwegian Earth System Model (NorESM), namely the Community Land Model (CLM5), has received substantial new implementations to help simulate the land surface processes in cold environments. At the same time, the behaviour of offline CLM5 simulations and new observational data sets have not been systematically compared over Scandinavian regions. In this study, we run the CLM5 model at relatively high resolution (0.25 degrees) over Scandinavia (including Svalbard) for 15 years between 2002 and 2016. We evaluate the water and energy budget components of CLM5 using several reanalyses and satellite-based observational data sets. In particular, we use monthly model outputs and compare with the satellite retrievals from GRACE, MODIS, AMSR2, and AMSR-E, and reanalysis data sets from ERA5, GLDAS, and MERRA-2. As an additional data source, we use the local‐scale measurements obtained from the Finse Eco-Hydrological Observatory (Finse EcHO) at 1200 m a.s.l, and the high-Arctic research site at Bayelva near Ny-Ålesund, Svalbard. Our investigation is focused on several variables including terrestrial water storage, snow water equivalent, turbulent fluxes, net radiation, and skin temperature. The results indicate that the perceived performance of the land surface model (CLM5) depends strongly on the reference observational data set. Regional discrepancies between data sets, particularly for Svalbard, prompts further investigation of the underlying sources of uncertainty. The results of this evaluation provide a valuable source of information for future studies in the region, particularly in the Land-ATmosphere Interactions in Cold Environments (LATICE) project, which focuses on cold region land surface dynamics, integrating across observational systems, laboratory experiments, field, and modeling efforts. Acknowledgement : This study is conducted under the LATICE strategic research initiative funded by the Faculty of Mathematics and Natural Sciences at the University of Oslo, and the project EMERALD (294948) funded by the Research Council of Norway.

• Bryn, Anders; Volden, Inger Kristine; Horvath, Peter; Torma, Michal & Stordal, Frode (2019). Hvor raskt stiger tre- og skoggrensene i Norge? Folkeforskning i praksis..
• Byre, Hanne Eline; Falk, Stefanie; Stordal, Frode & Berntsen, Terje Koren (2019). An Investigation of Source Regions Contributing to the Deposition of Reactive Nitrogen in Arctic and Boreal Areas. Show summary

  Long range atmospheric transport is an important source of reactive nitrogen (Nr) to Boreal and Artic ecosystems. The combined effect of climate change and deposition of reactive nitrogen which is an important nutriant for these systems, have the potential to change the carbon storage in high latitude reservoirs. Furthermore a change in vegetation, will lead to changes in the exchange of energy and humidity between the land surface and the atmosphere. We have conducted several model studies to investigate and quantify the importance and contribution of distinguished source regions to Nr deposition in polar and sub-polar regions in the northern hemisphere. Using a global chemistry transport model, we will assess the following questions: To what extent are emissions from agriculture in South-Asia affecting NOx deposition in the Arctic? What would happen if we shut down the automotive sector in Germany, do we see a reduction in the amount of NOx deposited in Norway?

• Falk, Stefanie; Stordal, Frode & Vollsnes, Ane Victoria (2019). Ozon und seine Auswirkungen auf die Vegetation in Nordskandinavien. Show summary

  Ozon ist eines der wichtigsten Spurengasen in der Atmosphäre. Während es uns in Form der Ozonschicht in der Stratosphäre vor schädlicher, kurzwelliger Strahlung schützt, zählt es in der planetaren Grenzschicht zu den überaus schädlichen Reizgasen. Eine Aufnahme einer Dosis von 50 ppm über die Dauer von 30 min gilt für den Menschen als tödlich. Pflanzen nehmen Ozon durch ihre Stoma auf, wo dieses zur Zerstörung von Zellen beiträgt, die der Photosynthese dienen, und letztlich Wachstum und Ertrag reduziert. Die empfindlichen Ökosysteme im Norden Skandinaviens erfahren bereits durch den Klimawandel einen erhöhten Stress. Sollte das Polarmeer dauerhaft eisfrei werden, so würde sich der Schiffsverkehr und damit die Menge der Ozonvorläufersubstanzen drastisch erhöhen. Insbesondere während des Polarsommers ist eine nächtliche Reparatur der entstandenen Ozonschäden gehindert. Wir präsentieren hier einen Überblick über die schädlichen Auswirkungen von Ozon auf Vegetation und erste Studien zu der Entwicklung von Ozonkonzentrationen in Nordskandinavien. Dabei greifen wir sowohl auf Langzeitmessungen als auch Modellsimulationen zurück.

• Guttu, Sigmund; Orsolini, Yvan; Stordal, Frode; Limpasuvan, Varavut & Marsh, D. (2019). Impact of medium-energy electron precipitation on ozone and middle atmosphere dynamics in WACCM simulations.
• Orsolini, Yvan; Guttu, Sigmund; Stordal, Frode & Limpasuvan, Varavut (2019). Impact of Medium-energy Electron Precipitation on Ozone and Middle Atmosphere Dynamics in WACCM Simulations.
• Pirk, Norbert; Ramtvedt, Eirik Næsset; Decker, Sven; Cassiani, Massimo; Burkhart, John; Stordal, Frode & Tallaksen, Lena M. (2019). Causes of surface energy imbalances of eddy covariance measurements in mountainous terrain.
• Stordal, Frode (2019). Ecosystem-climate interactions.
• Stordal, Frode (2019). Improved representation of ecosystem-climate interactions in NorESM.
• Stordal, Frode (2019). Interdisciplinary research in the EMERALD project.
• Stordal, Frode (2019). Our EMERALD planet: Terrestrial ecosystem-climate interactions.
• Stordal, Frode (2019). Terrestrial ecosystem-climate interactions of our EMERALD planet.
• Stordal, Frode (2019). Vegetation-climate interactions: observations and modelling.
• Stordal, Frode & Vollsnes, Ane Victoria (2019, 26. april). Eksos har skylden: Ozon på bakken skader avlingene. [Fagblad].  Apollon.
• Vollsnes, Ane Victoria; Stordal, Frode & Bhattacharjee, puja (2019, 09. mai). Ozone pollution from Asia isn't well understood, but may be damaging Arctic plants. [Internett].  www.firstpost.com/tech/science.
• Vollsnes, Ane Victoria; Stordal, Frode & Vogt, Yngve (2019, 26. april). Eksos har skylden: Ozon på bakken skader avlingene. [Tidsskrift].  Apollon.
• Yilmaz, Yeliz; Tallaksen, Lena M. & Stordal, Frode (2019). Assessment of the water and energy balance simulations of CTSM using satellite-based observations over Scandinavia.
• Haugnes, Gunhild M.; Tallaksen, Lena M.; Vogt, Rolf David; Storelvmo, Trude; Hessen, Dag Olav; Stordal, Frode; Lefevre, Sjannie; Kääb, Andreas & Uggerud, Einar (2018, 27. august). Klimaforskerne tar temperaturen på tropesommeren. [Tidsskrift].  Titan.uio.no.
• Hessen, Dag Olav; Stordal, Frode & Vogt, Rolf David (2018). Vi må forstå hvorfor to graders temperaturøkning er farlig. Aftenposten Vitenskap.  ISSN 2464-3033.
• Horvath, Peter; Halvorsen, Rune; Stordal, Frode; Tang, Hui & Bryn, Anders (2018). Distribution models of vegetation types in Norway.
• Kumkar, Yogesh; Astrup, Rasmus Andreas; Stordal, Frode; Tang, Hui & Bright, Ryan M. (2018). Investigating the sensitivity representation of forest management on surface energy and water fluxes in a land surface model.
• Orsolini, Yvan; Smith-Johnsen, Christine; Marsh, Dan & Stordal, Frode (2018). Chemical impacts of energetic particle precipitation in the middle atmosphere.
• Smith-Johnsen, Christine; Marsh, Daniel R.; Orsolini, Yvan; Nesse Tyssøy, Hilde; Sandanger, Marit Irene J.; Ødegaard, Linn-Kristine Glesnes & Stordal, Frode (2018). Nitric oxide response to the April 2010 electron precipitation event.
• Smith-Johnsen, Christine; Marsh, Daniel R.; Orsolini, Yvan; Tyssøy, Hilde Nesse; Hendrickx, Koen; Sandanger, Marit Irene J.; Ødegaard, Linn-Kristine Glesnes & Stordal, Frode (2018). Nitric oxide response to the April 2010 electron precipitation event - using WACCM and WACCM-D with and without medium energy electrons.
• Stordal, Frode; Berntsen, Terje Koren; Büker, Patrick; Falk, Stefanie; Rydsaa, Johanne Hope; Gillies, David & Vollsnes, Ane Victoria (2018). Ozone and climate stresses on sub-ARctic tundra vegetation: Modelling of stomatal fluxes in midnight sun.
• Thorarinsdottir, Thordis Linda; Lenkoski, Alex; Hellton, Kristoffer Herland; Steinbakk, Gunnhildur Högnadóttir; Dyrrdal, Anita Verpe; Stordal, Frode; Schlichting, Lena & Engeland, Kolbjørn (2018). On developing general and efficient inference algorithms for complicated hierarchical models.
• Vollsnes, Ane Victoria; Eriksen, Aud Berglen; Berntsen, Terje Koren; Kauserud, Håvard; Büker, Patrick; Emberson, Lisa D. & Stordal, Frode (2018). The double punch: ozone and climate stresses to sub-Arctic vegetation.
• Vollsnes, Ane Victoria; Eriksen, Aud Berglen; Büker, Patrick; Kauserud, Håvard; Falk, Stefanie & Stordal, Frode (2018). Ozone stress on sub-Arctic tundra vegetation: ozone exposure experiments with daylength manipulation..
• Vollsnes, Ane Victoria; Eriksen, Aud Berglen; Falk, Stefanie; Berntsen, Terje Koren; Kauserud, Håvard; Emberson, Lisa D. & Stordal, Frode (2018). Project The double punch: ozone and climate stresses on vegetation.
• Vollsnes, Ane Victoria; Eriksen, Aud Berglen; Falk, Stefanie; Bryn, Anders; Viken, Jeanette & Stordal, Frode (2018). Ozonforurensning. Klima, vegetasjon og matproduksjon.
• Vollsnes, Ane Victoria; Eriksen, Aud Berglen; Kauserud, Håvard; Berntsen, Terje Koren & Stordal, Frode (2018). The double punch: ozone and climate stresses on vegetation.
• Bryn, Anders; Potthoff, Kerstin; Horvath, Peter; Volden, Inger Kristine; Tang, Hui; Berntsen, Terje Koren & Stordal, Frode (2017). Greening and browning: 100 years of tree- and forest line dynamics..
• Bryn, Anders; Stordal, Frode; Berntsen, Terje Koren & Tang, Hui (2017). Vegetation dynamics - distribution, modelling and feedbacks..
• Bryn, Anders; Volden, Inger Kristine; Horvath, Peter & Stordal, Frode (2017). Skogen er på fjelltur. Aftenposten (morgenutg. : trykt utg.).  ISSN 0804-3116.  s 12- 13
• Buker, Patrick; Stordal, Frode; Vedeld, Trond; Mathur, Mihir & Bhadwal, Suruchi (2017). Preparing Indian agriculture for short- to long-term changes in weather and climate: The role of climate services in crop models.
• Horvath, Peter; Tang, Hui; Stordal, Frode & Bryn, Anders (2017). Terrestrial vegetation ecological climatology.
• Jeanette, Viken; Vollsnes, Ane Victoria; Eriksen, Aud Else Berglen; Berntsen, Terje Koren & Stordal, Frode (2017). DO3SEiNORD.
• Nilsen, Irene Brox; Tallaksen, Lena M. & Stordal, Frode (2017). Potential feedbacks between snow cover, soil moisture and surface energy fluxes in Southern Norway. Show summary

  At high latitudes, the snow season has become shorter during the past decades because snowmelt is highly sensitive to a warmer climate. Snowmelt influences the energy balance by changing the albedo and the partitioning between latent and sensible heat fluxes. It further influences the water balance by changing the runoff and soil moisture. In a previous study, we identified southern Norway as a region where significant temperature changes in summer could potentially be explained by land-atmosphere interactions. In this study we hypothesise that changes in snow cover would influence the summer surface fluxes in the succeeding weeks or months. The exceptionally warm summer of 2014 was chosen as a test bed. In Norway, evapotranspiration is not soil moisture limited, but energy limited, under normal conditions. During warm summers, however, such as in 2014, evapotranspiration can be restricted by the available soil moisture. Using the Weather Research and Forecasting (WRF) model we replace the initial ground conditions for 2014 with conditions representative of a snow-poor spring and a snow-rich spring. WRF was coupled to Noah-MP at 3 km horizontal resolution in the inner domain, and the simulations covered mid-May through September 2014. Boundary conditions used to force WRF were taken from the Era-Interim reanalysis. Snow, runoff, soil moisture and soil temperature observational data were provided by the Norwegian Water Resources and Energy Directorate for validation. The validation shows generally good agreement with observations. Preliminary results show that the reduced snowpack, hereafter “sim1” increased the air temperature by up to 5 K and the surface temperature by up to 10 K in areas affected by snow changes. The increased snowpack, hereafter “sim2”, decreased the air and surface temperature by the same amount. These are weekly mean values for the first eight simulation weeks from mid May. Because of the higher net energy available (∼ 100 Wm-2) in sim 1, both the evapotranspiration and sensible heat fluxes increased. In sim 2, they decreased because of lower net energy. The ground heat flux decreased in sim1 (and increased in sim2). Large increases were seen in runoff, both surface and underground runoff, during the first weeks of sim2 (from mid May), but the timing of snowmelt was only slightly affected. This study contributes to a greater understanding of land-atmosphere interactions in a wet, temperate climate, in particular the role of snow cover (and snowmelt) and its feedback to the atmosphere.

• Rydsaa, Johanne Hope; Stordal, Frode; Bryn, Anders & Tallaksen, Lena M. (2017). Effects of shrub cover changes on the near surface atmosphere in northern Fennoscandia: A model study..
• Smith-Johnsen, Christine; Tyssøy, Hilde Nesse; Hendrickx, Koen; Orsolini, Yvan; Kishore Kumar, Grandhi; Ødegaard, Linn-Kristine Glesnes; Stordal, Frode & Megner, Linda (2017). Direct and indirect electron precipitation effect on nitric oxide, using a full range energy spectrum.
• Stordal, Frode; Tang, Hui; Berntsen, Terje Koren; Büker, Patrick; Vollsnes, Ane Victoria; Eriksen, Aud Berglen & Kauserud, Håvard (2017). Modelling combined effects of ozone and climate stresses on Arctic and boreal species.
• Tang, Hui; Stordal, Frode; Berntsen, Terje Koren & Bryn, Anders (2017). Improve dynamic vegetation model of community land model in simulating Arctic vegetation and its interaction with climate..
• Tang, Hui; Zhou, Liping & Stordal, Frode (2017). Tracing soil organic carbon isotopes and their response to grazing exclusion in a temperate grassland of northern China using Community Land model (CLM4.5).
• Tyssøy, Hilde Nesse; Smith-Johnsen, Christine; Orsolini, Yvan; Marsh, Daniel R.; Hendrickx, Koen; Sandanger, Marit Irene J.; Ødegaard, Linn-Kristine Glesnes; Kishore Kumar, Grandhi; Stordal, Frode & Megner, Linda (2017). Direct and indirect electron precipitation effect on nitric oxide during the April 2010 electron precipitation events, Part 1: Observations, Part 2: WACCM.
• Bryn, Anders; Rekdal, Yngve; Moen, Asbjørn & Stordal, Frode (2016). Store kunnskapshull i myra. Nationen.  ISSN 0805-3782.  s 18- 18
• Mtongori, Habiba Ismail; Stordal, Frode; Benestad, Rasmus; Pereira-Flores, Milton E & Justino, Flavio (2016). Impacts of climate change and variability on yields for selected maize cultivars in Southern Tanzania.
• Smith-Johnsen, Christine; Marsh, Daniel R.; Orsolini, Yvan; Tyssøy, Hilde Nesse; Hendrickx, Koen; Ødegaard, Linn-Kristine Glesnes; Stordal, Frode & Megner, Linda (2016). NO produced by energetic electron precipitation during a geomagnetic storm in April 2010- model vs observations.
• Smith-Johnsen, Christine; Tyssøy, Hilde Nesse; Ødegaard, Linn-Kristine Glesnes; Kishore Kumar, Grandhi; Orsolini, Yvan; Stordal, Frode; Hendrickx, Koen; Megner, Linda & Marszalek, Markus (2016). NO produced by energetic electron precipitation during a geomagnetic storm in April 2010NO produced by energetic electron precipitation during a geomagnetic storm in April 2010.
• Tang, Hui; Stordal, Frode; Berntsen, Terje Koren & Bryn, Anders (2016). Dynamical vegetation-atmosphere modelling of the boreal zone.
• Justino, Flavio; Silva, Antônio Simões; Pereira, Marcos Paulo Santos; Stordal, Frode; Lindemann, Douglas Da Silva & Kucharski, Fred (2015). Corrigendum to "The large-scale climate in response to the retreat of the West Antarctic ice sheet" [J. Climate, 28, (2015), 637-650] doi:10.1175/JCLI-D-14-00284.1. Journal of Climate.  ISSN 0894-8755.  28(9), s 3902- 3903 . doi: 10.1175/JCLI-D-15-0157.1
• Smith-Johnsen, Christine; Tyssøy, Hilde Nesse; Ødegaard, Linn-Kristine Glesnes; Stordal, Frode; Orsolini, Yvan; Hendrickx, Koen & Megner, Linda (2015). Nitric oxide produced by energetic electron precipitation during a geomagnetic storm in April 2010.
• Stordal, Frode (2015). Climate change: From science to services.
• Engdahl, Bjørg Jenny Kokkvoll; Velken, Anna von Streng; Berglen, Tore Flatlandsmo; Hodnebrog, Øivind & Stordal, Frode (2014). Utslipp, spredning og avsetning av SO2 fra Nikel og Zapoljarnij. En WRF-Chem modellstudie.. NILU OR (NILU Oppdragsrapport). 57/2014. Full text in Research Archive. Show summary

  WRF-Chem-modellen har blitt brukt for å studere to episoder med forurensning fra smelteverkene i Nikel og Zapoljarnij, sommerepisoden 2007 og vinteren 2010/11. Meteorologiske inngangsdata fra WRF stemmer bra med analyse fra ECMWF. Modellen underestimerer SO2-konsentrasjoner i episoder, en mulig forklaring er at røykfanen blir midlet ut i modellen, samt at tidsutviklingen av utslippene ikke er korrekt representert. Budsjett over kilder og sluk viser at kjemisk tap er viktigst om sommeren, fulgt av våtavsetning, men våt- og tørravsetning er viktigst om vinteren. WRF-Chem er meget regnekrevende og oppsummert er WRF-Chem best egnet til å studere prosesser og enkeltepisoder.

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