Frode Stordal

• 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, s 1- 17 . doi: 10.3389/feart.2019.00178
• 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. . doi: 10.1111/avsc.12451 Show summary

  Aim Many countries lack informative and 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 117 explanatory variables, recorded in 100×100‐m grid cells, were used. The 31 models were evaluated by applying the AUC criterion to 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 better predicted than common ones, and coastal VTs are better predicted 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
• 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 - 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 - 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 - 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.

• Justino, Flavio; Marengo, Jose Antonio; Kucharski, Fred; Stordal, Frode; Machado, Jeferson Prietsch & Rodrigues, M. (2014). Influence of Antarctic ice sheet lowering on the Southern Hemisphere climate: Modeling experiments mimicking the mid-Miocene. Climate Dynamics.  ISSN 0930-7575.  42(3-4), s 843- 858 . doi: 10.1007/s00382-013-1689-9
• Sukumaran, Sandeep; Stordal, Frode; Sardeshmukh, Prashant D. & Compo, Gilbert P. (2014). Pacific Walker Circulation variability in coupled and uncoupled climate models. Climate Dynamics.  ISSN 0930-7575.  43(1-2), s 103- 117 . doi: 10.1007/s00382-014-2135-3
• Endris, Hussen Seid; Omondi, Philip; Jain, Suman; Lennard, Christopher; Hewitson, Bruce; Chang'a, Ladislaus; Awange, Joseph Langat; Dosio, Alessandro; Ketiem, Patrick; Nikulin, Grigory; Panitz, Hans-Jürgen; Büchner, Matthias; Stordal, Frode & Tazalika, Lukiya (2013). Assessment of the Performance of CORDEX Regional Climate Models in Simulating East African Rainfall. Journal of Climate.  ISSN 0894-8755.  26(21), s 8453- 8475 . doi: 10.1175/JCLI-D-12-00708.1
• Hilboll, A.; Richter, A.; Rozanov, A.; Hodnebrog, Øivind; Heckel, A.; Solberg, Sverre; Stordal, Frode & Burrows, J.P. (2013). Improvements to the retrieval of tropospheric NO2 from satellite - stratospheric correction using SCIAMACHY limb/nadir matching and comparison to Oslo CTM2 simulations. Atmospheric Measurement Techniques.  ISSN 1867-8548.  6(3), s 565- 584 . doi: 10.5194/amt-6-565-2013 Full text in Research Archive.
• Sukumaran, Sandeep & Stordal, Frode (2013). Use of daily outgoing longwave radiation (OLR) data in detecting precipitation extremes in the tropics. IEEE Geoscience and Remote Sensing Letters.  ISSN 1545-598X.  4(6), s 570- 578 . doi: 10.1080/2150704X.2013.769284
• Tweedy, Olga V.; Limpasuvan, Varavut; Orsolini, Yvan; Smith, Anne K.; Garcia, Rolando R.; Kinnison, Doug; Randall, Cora E.; Kvissel, Ole-Kristian; Stordal, Frode; Harvey, V. Lynn & Chandran, Amal (2013). Nighttime secondary ozone layer during major stratospheric sudden warmings in specified-dynamics WACCM. Journal of Geophysical Research - Atmospheres.  ISSN 2169-897X.  118(15), s 8346- 8358 . doi: 10.1002/jgrd.50651
• von Hobe, Marc; Bekki, S.; Borrmann, S.; Cairo, F.; D'Amato, F.; Di Donfrancesco, G; Dörnbrack, A.; Ebersoldt, A.; Ebert, M.; Emde, C.; Engel, I.; Ern, Manfred; Frey, W.; Genco, S.; Griessbach, S.; Grooß, J.-U.; Gulde, T.; Günther, G.; Hösen, E.; Hoffmann, L.; Homonnai, V.; Hoyle, Christopher; Isaksen, Ivar S A; Jackson, D.R.; Jánosi, I. M.; Jones, R.L.; Kandler, K; Kalicinsky, C.; Keil, A.; Khaykin, S. M.; Khosrawi, F.; Kivi, R.; Kuttippurath, J.; Laube, J. C.; Lefevre, F; Lehmann, R.; Ludmann, S.; Luo, BP; Marchand, M.; Meyer, J.; Mitev, V; Molleker, S.; Müller, R.; Oelhaf, H.; Olschewski, F.; Orsolini, Yvan; Peter, T.; Pfeilsticker, K.; Piesch, C.; Pitts, Mike C.; Poole, Lamont R.; Pope, F. D.; Ravegnani, F.; Rex, M.; Riese, M.; Rockmann, T; Rognerud, Bjørg; Roiger, A.; Rolf, C.; Santee, M. L.; Scheibe, M; Schiller, C.; Schlager, H.; Siciliani de Cumis, M.; Sitnikov, N.; Søvde, Ole Amund; Spang, R.; Spelten, N.; Stordal, Frode; Sumińska-Ebersoldt, O.; Ulanovski, A.; Ungermann, J.; Viciani, S.; Volk, C.M.; vom Scheidt, M.; von der Gathen, P.; Walker, K.; Wegner, T.; Weigel, R.; Weinbuch, S.; Wetzel, G.; Wienhold, F. G.; Wohltmann, I.; Woiwode, W.; Young, I. A. K.; Yushkov, V.; Zobrist, B. & Stroh, F. (2013). Reconciliation of essential process parameters for an enhanced predictability of Arctic stratospheric ozone loss and its climate interactions (RECONCILE): activities and results. Atmospheric Chemistry and Physics.  ISSN 1680-7316.  13(18), s 9233- 9268 . doi: 10.5194/acp-13-9233-2013 Full text in Research Archive.
• Hodnebrog, Øivind; Solberg, Sverre; Stordal, Frode; Svendby, Tove Marit; Simpson, David; Gauss, Michael; Hilboll, Andreas; Pfister, G.; Turquety, Solène; Richter, Andreas; Burrows, John P. & Denier van der Gon, H. A. C. (2012). Impact of forest fires, biogenic emissions and high temperatures on the elevated Eastern Meditteranean ozone levels during the hot summer of 2007. Atmospheric Chemistry and Physics.  ISSN 1680-7316.  12(18), s 8727- 8750 . doi: 10.5194/acp-12-8727-2012 Full text in Research Archive. Show summary

  The hot summer of 2007 in southeast Europe has been studied using two regional atmospheric chemistry models; WRF-Chem and EMEP MSC-W. The region was struck by three heat waves and a number of forest fire episodes, greatly affecting air pollution levels. We have focused on ozone and its precursors using state-of-the-art inventories for anthropogenic, biogenic and forest fire emissions. The models have been evaluated against measurement data, and processes leading to ozone formation have been quantified. Heat wave episodes are projected to occur more frequently in a future climate, and therefore this study also makes a contribution to climate change impact research. The plume from the Greek forest fires in August 2007 is clearly seen in satellite observations of CO and NO2 columns, showing extreme levels of CO in and downwind of the fires. Model simulations reflect the location and influence of the fires relatively well, but the modelled magnitude of CO in the plume core is too low. Most likely, this is caused by underestimation of CO in the emission inventories, suggesting that the CO/NOx ratios of fire emissions should be re-assessed. Moreover, higher maximum values are seen in WRF-Chem than in EMEP MSC-W, presumably due to differences in plume rise altitudes as the first model emits a larger fraction of the fire emissions in the lowermost model layer. The model results are also in fairly good agreement with surface ozone measurements. Biogenic VOC emissions reacting with anthropogenic NOx emissions are calculated to contribute significantly to the levels of ozone in the region, but the magnitude and geographical distribution depend strongly on the model and biogenic emission module used. During the July and August heat waves, ozone levels increased substantially due to a combination of forest fire emissions and the effect of high temperatures. We found that the largest temperature impact on ozone was through the temperature dependence of the biogenic emissions, closely followed by the effect of reduced dry deposition caused by closing of the plants’ stomata at very high temperatures. The impact of high temperatures on the ozone chemistry was much lower. The results suggest that forest fire emissions, and the temperature effect on biogenic emissions and dry deposition, will potentially lead to substantial ozone increases in a warmer climate.

• Colette, Augustin; Granier, C; Hodnebrog, Øivind; Jakobs, Hermann; Maurizi, Alberto; Nyiri, Agnes; Rao, S; Amann, M; Bessagnet, Bertrand; D'Angiola, Ariela; Gauss, Michael; Heyes, C; Klimont, Z; Meleux, Frederik; Memmesheimer, Michael; Mieville, A; Rouil, Laurence; Russo, F; Schucht, S; Simpson, D; Stordal, Frode; Tampieri, Francesco & Vrac, M (2012). Future air quality in Europe: a multi-model assessment of projected exposure to ozone. Atmospheric Chemistry and Physics.  ISSN 1680-7316.  12(21), s 10613- 10630 . doi: 10.5194/acp-12-10613-2012
• Giorgi, F.; Coppola, E.; Solmon, F.; Mariotti, L.; Sylla, M.B.; Bi, X.; Elguindi, N.; Diro, G.T.; Nair, V.; Giuliani, G.; Turuncoglu, U.U.; Cozzini, S.; Guttler, I.; O'Brien, T.A.; Tawfik, A.B.; Shalaby, A.; Zakey, A.S.; Steiner, A.L.; Stordal, Frode; Sloan, L.C. & Brankovic, C. (2012). RegCM4: model description and preliminary tests over multiple CORDEX domains. Climate Research (CR).  ISSN 0936-577X.  52(1), s 7- 29 . doi: 10.3354/cr01018
• Hodnebrog, Øivind; Berntsen, Terje Koren; Dessens, O.; Gauss, Michael; Grewe, V; Isaksen, Ivar S A; Koffi, B.; Myhre, Gunnar; Oliviè, Dirk Jan Leo; Prather, M; Stordal, Frode; Szopa, S; Tang, Q; van Velthoven, P & Williams, J (2012). Future impact of traffic emissions on atmospheric ozone and OH based on two scenarios. Atmospheric Chemistry and Physics.  ISSN 1680-7316.  12(24), s 12211- 12225 . doi: 10.5194/acp-12-12211-2012 Show summary

  The future impact of traffic emissions on atmospheric ozone and OH has been investigated separately for the three sectors AIRcraft, maritime SHIPping and ROAD traffic. To reduce uncertainties we present results from an ensemble of six different atmospheric chemistry models, each simulating the atmospheric chemical composition in a possible high emission scenario (A1B), and with emissions from each transport sector reduced by 5% to estimate sensitivities. Our results are compared with optimistic future emission scenarios (B1 and B1 ACARE), presented in a companion paper, and with the recent past (year 2000). Present-day activity indicates that anthropogenic emissions so far evolve closer to A1B than the B1 scenario. As a response to expected changes in emissions, AIR and SHIP will have increased impacts on atmospheric O3 and OH in the future while the impact of ROAD traffic will decrease substantially as a result of technological improvements. In 2050, maximum aircraft-induced O3 occurs near 80° N in the UTLS region and could reach 9 ppbv in the zonal mean during summer. Emissions from ship traffic have their largest O3 impact in the maritime boundary layer with a maximum of 6 ppbv over the North Atlantic Ocean during summer in 2050. The O3 impact of road traffic emissions in the lower troposphere peaks at 3 ppbv over the Arabian Peninsula, much lower than the impact in 2000. Radiative forcing (RF) calculations show that the net effect of AIR, SHIP and ROAD combined will change from a marginal cooling of −0.44 ± 13 mW m−2 in 2000 to a relatively strong cooling of −32 ± 9.3 (B1) or −32 ± 18 mW m−2 (A1B) in 2050, when taking into account RF due to changes in O3, CH4 and CH4-induced O3. This is caused both by the enhanced negative net RF from SHIP, which will change from −19 ± 5.3 mW m−2 in 2000 to −31 ± 4.8 (B1) or −40 ± 9 mW m−2 (A1B) in 2050, and from reduced O3 warming from ROAD, which is likely to turn from a positive net RF of 12 ± 8.5 mW m−2 in 2000 to a slightly negative net RF of −3.1 ± 2.2 (B1) or −3.1 ± 3.4 (A1B) mW m−2 in the middle of this century. The negative net RF from ROAD is temporary and induced by the strong decline in ROAD emissions prior to 2050, which only affects the methane cooling term due to the longer lifetime of CH4 compared to O3. The O3 RF from AIR in 2050 is strongly dependent on scenario and ranges from 19 ± 6.8 (B1 ACARE) to 61 ± 14 mW m−2 (A1B). There is also a considerable span in the net RF from AIR in 2050, ranging from −0.54 ± 4.6 (B1 ACARE) to 12 ± 11 (A1B) mW m−2 compared to 6.6 ± 2.2 mW m−2 in 2000.

• Isaksen, Ivar S A; Zerefos, C; Wang, W-C; Balis, D.; Eleftheratos, K.; Rognerud, Bjørg; Stordal, Frode; Berntsen, Terje Koren; Lacasce, Joseph Henry; Søvde, Ole Amund; Oliviè, Dirk Jan Leo; Orsolini, Yvan; Zyrichidou, I.; Prather, M.J. & Tuinder, O. N. E. (2012). Attribution of the Arctic ozone column deficit in March 2011. Geophysical Research Letters.  ISSN 0094-8276.  39(L24810) . doi: 10.1029/2012GL053876 Show summary

  Arctic column ozone reached record low values (∼310 DU) during March of 2011, exposing Arctic ecosystems to enhanced UV-B. We identify the cause of this anomaly using the Oslo CTM2 atmospheric chemistry model driven by ECMWF meteorology to simulate Arctic ozone from 1998 through 2011. CTM2 successfully reproduces the variability in column ozone, from week to week, and from year to year, correctly identifying 2011 as an extreme anomaly over the period. By comparing parallel model simulations, one with all Arctic ozone chemistry turned off on January 1, we find that chemical ozone loss in 2011 is enhanced relative to previous years, but it accounted for only 23% of the anomaly. Weakened transport of ozone from middle latitudes, concurrent with an anomalously strong polar vortex, was the primary cause of the low ozone When the zonal winds relaxed in mid-March 2011, Arctic column ozone quickly recovered.

• Kvissel, Ole-Kristian; Orsolini, Yvan; Stordal, Frode; Isaksen, Ivar S A & Santee, Michelle L. (2012). Formation of stratospheric nitric acid by a hydrated ion cluster reaction: Implications for the effect of energetic particle precipitation on the middle atmosphere. Journal of Geophysical Research - Atmospheres.  ISSN 2169-897X.  117 . doi: 10.1029/2011JD017257
• Kvissel, Ole-Kristian; Orsolini, Yvan; Stordal, Frode; Limpasuvan, Varavut; Richter, Jadwiga H. & Marsh, Daniel R. (2012). Mesospheric intrusion and anomalous chemistry during and after a major stratospheric sudden warming. Journal of Atmospheric and Solar-Terrestrial Physics.  ISSN 1364-6826.  78-79, s 116- 124 . doi: 10.1016/j.jastp.2011.08.015
• Limpasuvan, Varavut; Richter, Jadwiga H.; Orsolini, Yvan; Stordal, Frode & Kvissel, Ole-Kristian (2012). The roles of planetary and gravity waves during a major stratospheric sudden warming as characterized in WACCM. Journal of Atmospheric and Solar-Terrestrial Physics.  ISSN 1364-6826.  78-79, s 84- 98 . doi: 10.1016/j.jastp.2011.03.004
• Lindholm, Markus; Stordal, Frode; Moe, S. Jannicke; Hessen, Dag Olav & Aass, Per (2012). Climate-driven range retraction of an Arctic freshwater crustacean. Freshwater Biology.  ISSN 0046-5070.  57(12), s 2591- 2601 . doi: 10.1111/fwb.12030
• Shalaby, Ahmed; Zakey, Ashraf S.; Tawfik, Ahmed B.; Solmon, Fikreab; Giorgi, Filippo; Stordal, Frode; Sillman, Sanford; Zaveri, Rahul A. & Steiner, Allison L. (2012). Implementation and evaluation of online gas-phase chemistry within a regional climate model (RegCM-CHEM4). Geoscientific Model Development.  ISSN 1991-959X.  5(3), s 741- 760 . doi: 10.5194/gmd-5-741-2012
• Sylla, M.B.; Giorgi, F. & Stordal, Frode (2012). Large-scale origins of rainfall and temperature bias in high-resolution simulations over southern Africa. Climate Research (CR).  ISSN 0936-577X.  52(1), s 193- 211 . doi: 10.3354/cr01044
• Søvde, Ole Amund; Prather, M.J.; Isaksen, Ivar S A; Berntsen, Terje Koren; Stordal, Frode; Zhu, Xin; Holmes, Chris D. & Hsu, Juno (2012). The chemical transport model Oslo CTM3. Geoscientific Model Development.  ISSN 1991-959X.  5, s 1441- 1469 . doi: 10.5194/gmd-5-1441-2012 Show summary

  We present here the global chemical transport model Oslo CTM3, an update of the Oslo CTM2. The update comprises a faster transport scheme, an improved wet scavenging scheme for large scale rain, updated photolysis rates and a new lightning parameterization. Oslo CTM3 is better parallelized and allows for stable, large time steps for advection, enabling more complex or high spatial resolution simulations. A new treatment of the horizontal distribution of lightning is presented and found to compare well with measurements. The vertical distribution of lightning is updated and found to be a large contributor to CTM2–CTM3 differences, producing more NOx in the tropical middle troposphere, and less at the surface and at high altitudes. Compared with Oslo CTM2, Oslo CTM3 is faster, more capable and has better conceptual models for scavenging, vertical transport and fractional cloud cover. CTM3 captures stratospheric O3 better than CTM2, but shows minor improvements in terms of matching atmospheric observations in the troposphere. Use of the same meteorology to drive the two models shows that some features related to transport are better resolved by the CTM3, such as polar cap transport, while features like transport close to the vortex edge are resolved better in the Oslo CTM2 due to its required shorter transport time step. The longer transport time steps in CTM3 result in larger errors, e.g., near the jets, and when necessary the errors can be reduced by using a shorter time step. Using a time step of 30 min, the new transport scheme captures both large-scale and small-scale variability in atmospheric circulation and transport, with no loss of computational efficiency. We present a version of the new transport scheme which has been specifically tailored for polar studies, resulting in more accurate polar cap transport than the standard CTM3 transport, confirmed by comparison to satellite observations. Inclusion of tropospheric sulfur chemistry and nitrate aerosols in CTM3 is shown to be important to reproduce tropospheric O3, OH and the CH4 lifetime well.

• Yao, Bo; Vollmer, Martin K; Xia, Lingjun; Zhou, Lingxi; Simmonds, Peter G; Stordal, Frode; Maione, Michela; Reimann, Stefan & O'Doherty, Simon (2012). A study of four-year HCFC-22 and HCFC-142b in-situ measurements at the Shangdianzi regional background station in China. Atmospheric Environment.  ISSN 1352-2310.  63, s 43- 49 . doi: 10.1016/j.atmosenv.2012.09.011
• Aamaas, Borgar; Bøggild, Carl Egede; Stordal, Frode; Berntsen, Terje Koren; Holmén, Kim Johan & Ström, Johan (2011). Elemental carbon deposition to Svalbard snow from Norwegian settlements and long-range transport. Tellus. Series B, Chemical and physical meteorology.  ISSN 0280-6509.  63(3), s 340- 351 . doi: 10.1111/j.1600-0889.2011.00531.x Show summary

  The impact on snow pack albedo from local elemental carbon (EC) sources in Svalbard has been investigated for the winter of 2008. Highly elevated EC concentrations in the snow are observed around the settlements of Longyearbyen and Svea (locally >1000 ng g−1, about 200 times over the background level), while EC concentrations similar to the background level are seen around Ny-Ålesund. Near Longyearbyen and Svea, darkened snow influenced by wind transported coal dust from open coal stockpiles is clearly visible from satellite images and by eye at the ground. As a first estimate, the reduction in snow albedo caused by local EC pollution from the Norwegian settlements has been compared to the estimated reduction caused by long-range transported EC for entire Svalbard. The effect of local EC from Longyearbyen, Svea and all Norwegian settlements are estimated to 2.1%, 7.9% and 10% of the total impact of EC, respectively. The EC particles tend to stay on the surface during melting, and elevated EC concentrations due to the spring melt was observed. This accumulation of EC enhances the positive albedo feedbacks. The EC concentrations were observed to be larger in metamorphosed snow than in fresh snow, and especially around ice lenses.

• Balis, D.; Isaksen, Ivar S A; Zerefos, C.S.; Zyrichidou, I.; Eleftheratos, K.; Tourpali, K.; Bojkov, R.; Rognerud, Bjørg; Stordal, Frode; Søvde, Amund & Orsolini, Yvan (2011). Observed and modelled record ozone decline over the Arctic during winter/spring 2011. Geophysical Research Letters.  ISSN 0094-8276.  38(L23801) . doi: 10.1029/2011GL049259 Show summary

  This work describes observational and modelling results of the ozone depletion which took place during the winter/spring of 2011 in the Arctic stratosphere. Assimilated total ozone data from GOME-2 were used to estimate the integrated ozone mass deficit at polar latitudes and the Oslo CTM2 model calculated low winter/spring ozone values over the Arctic, which compare well with the satellite observations. Model runs with and without chemistry in the Arctic during the winter/spring of 2011 show that the very low Arctic stratospheric air temperatures led to significant chemical ozone loss. The calculated winter/spring ozone mass deficit (O3MD) reached extreme high values in 2011 (2700 Mt) and the seasonal zonal mean total ozone extreme low values of 333DU. Dynamics have set up the conditions for cold temperatures in the lower stratosphere in winter/spring of 2011. Comparison of ozone columns with the previous 13 years shows record low ozone column values during winter/spring in the Arctic in 2011. A comparison is also given with similar model studies for the overall warmer winter/spring of 2010 which show higher ozone column values and significantly less chemical ozone loss. The interannual variability of column ozone over the northern polar region is, as expected, highly correlated with the corresponding year-to-year variability of the seasonally-averaged temperatures in the lower stratosphere.

• Colette, Augustin; Granier, Claire; Hodnebrog, Øivind; Jakobs, Hermann; Maurizi, Alberto; Nyiri, Agnes; Bessagnet, Bertrand; D'Angiola, Ariela; D'Isidoro, Massimo; Gauss, Michael; Meleux, Frederik; Memmesheimer, Michael; Mieville, Aude; Rouil, Laurence; Russo, Felicita; Solberg, Sverre; Stordal, Frode & Tampieri, Francesco (2011). Air quality trends in Europe over the past decade: a first multi-model assessment. Atmospheric Chemistry and Physics.  ISSN 1680-7316.  11(22), s 11657- 11678 . doi: 10.5194/acp-11-11657-2011 Full text in Research Archive.
• Hodnebrog, Øivind; Berntsen, Terje Koren; Dessens, Olivier; Gauss, Michael; Grewe, Volker; Isaksen, Ivar S A; Koffi, Brigitte; Myhre, Gunnar; Olivie, Dirk Jan Leo; Prather, Michael J; Pyle, John A.; Stordal, Frode; Szopa, Sophie; Tang, Qi; van Velthoven, Peter; Williams, Jason E & Ødemark, Karianne (2011). Future impact of non-land based traffic emissions on atmospheric ozone and OH - an optimistic scenario and a possible mitigation strategy. Atmospheric Chemistry and Physics.  ISSN 1680-7316.  11(21), s 11293- 11317 . doi: 10.5194/acp-11-11293-2011 Show summary

  The impact of future emissions from aviation and shipping on the atmospheric chemical composition has been estimated using an ensemble of six different atmospheric chemistry models. This study considers an optimistic emission scenario (B1) taking into account e.g. rapid introduction of clean and resource-efficient technologies, and a mitigation option for the aircraft sector (B1 ACARE), assuming further technological improvements. Results from sensitivity simulations, where emissions from each of the transport sectors were reduced by 5%, show that emissions from both aircraft and shipping will have a larger impact on atmospheric ozone and OH in near future (2025; B1) and for longer time horizons (2050; B1) compared to recent time (2000). However, the ozone and OH impact from aircraft can be reduced substantially in 2050 if the technological improvements considered in the B1 ACARE will be achieved. Shipping emissions have the largest impact in the marine boundary layer and their ozone contribution may exceed 4 ppbv (when scaling the response of the 5% emission perturbation to 100% by applying a factor 20) over the North Atlantic Ocean in the future (2050; B1) during northern summer (July). In the zonal mean, ship-induced ozone relative to the background levels may exceed 12% near the surface. Corresponding numbers for OH are 6.0 × 105 molecules cm−3 and 30%, respectively. This large impact on OH from shipping leads to a relative methane lifetime reduction of 3.92 (±0.48) on the global average in 2050 B1 (ensemble mean CH4 lifetime is 8.0 (±1.0) yr), compared to 3.68 (±0.47)% in 2000. Aircraft emissions have about 4 times higher ozone enhancement efficiency (ozone molecules enhanced relative to NOx molecules emitted) than shipping emissions, and the maximum impact is found in the UTLS region. Zonal mean aircraft-induced ozone could reach up to 5 ppbv at northern mid- and high latitudes during future summer (July 2050; B1), while the relative impact peaks during northern winter (January) with a contribution of 4.2%. Although the aviation-induced impact on OH is lower than for shipping, it still causes a reduction in the relative methane lifetime of 1.68 (±0.38)% in 2050 B1. However, for B1 ACARE the perturbation is reduced to 1.17 (±0.28)%, which is lower than the year 2000 estimate of 1.30 (±0.30)%. Based on the fully scaled perturbations we calculate net radiative forcings from the six models taking into account ozone, methane (including stratospheric water vapour), and methane-induced ozone changes. For the B1 scenario, shipping leads to a net cooling with radiative forcings of −28.0 (±5.1) and −30.8 (±4.8) mW m−2 in 2025 and 2050, respectively, due to the large impact on OH and, thereby, methane lifetime reductions. Corresponding values for the aviation sector shows a net warming effect with 3.8 (±6.1) and 1.9 (±6.3) mW m−2, respectively, but with a small net cooling of -0.6 (±4.6) mW m−2 for B1 ACARE in 2050.

• Hodnebrog, Øivind; Stordal, Frode & Berntsen, Terje Koren (2011). Does the resolution of megacity emissions impact large scale ozone?. Atmospheric Environment.  ISSN 1352-2310.  45(38), s 6852- 6862 . doi: 10.1016/j.atmosenv.2011.01.012
• Roscher, Marco; Stordal, Frode & Svensen, Henrik (2011). The effect of global warming and global cooling on the distribution of the latest Permian climate zones. Palaeogeography, Palaeoclimatology, Palaeoecology.  ISSN 0031-0182.  309(3-4), s 186- 200 . doi: 10.1016/j.palaeo.2011.05.042
• Søvde, Ole Amund; Orsolini, Yvan; Jackson, D.R.; Stordal, Frode; Isaksen, Ivar S A & Rognerud, Bjørg (2011). Estimation of Arctic O-3 loss during winter 2006/2007 using data assimilation and comparison with a chemical transport model. Quarterly Journal of the Royal Meteorological Society.  ISSN 0035-9009.  137(654), s 118- 128 . doi: 10.1002/qj.740 Show summary

  The evolution of Arctic stratospheric O3 throughout the winter and spring of 2006/2007 is estimated by a state-of-the-art chemical transport model (CTM) and by a 3D-Var assimilation system using O3 data from the Earth Observing System (EOS) Microwave Limb Sounder (MLS) and Solar Backscatter Ultraviolet Radiometer (SBUV/2) satellites. Modelled and assimilated O3 compare well with MLS measurements. The aim of this article is to compare O3 loss estimates derived from the CTM and data-assimilation results, and as a result point to further developments in the method of inferring O3 loss using data assimilation. The methods for inferring O3 loss are discussed and compared with other published methods. The assimilation-system vertical transport is found to be too fast, in agreement with an earlier study, although this affects only the O3 reference field used for the loss estimation. Improving the O3 reference in the assimilation method used here provides a maximum vortex average O3 loss range of 0.8–1.2 ppmv at 68 hPa and 1.0–1.5 ppmv at 46 hPa, peaking at the beginning of March. The corresponding CTM values are 1.4 and 1.6 ppmv, respectively, with the peak lagging the assimilation by a few days at 46 hPa. We show that using a passive tracer as reference for O3 loss does not provide the best estimate for polar stratospheric cloud (PSC)-related loss for this winter; up to 40% of total O3 loss is shown not to be related to PSCs or heterogenous chemistry. Hence, the use of a passive O3 reference for estimating PSC-related O3 loss should be made with care. In addition to the vortex average losses, we estimate an innermost vortex O3 loss of 1.4 ppmv due to PSCs only. Transport effects and differences between the CTM and the assimilation system are discussed, and possible improvements for both models are suggested.

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• Bryn, Anders; Volden, Inger Kristine; Horvath, Peter; Torma, Michal & Stordal, Frode (2019). Hvor raskt stiger tre- og skoggrensene i Norge? Folkeforskning i praksis..
• 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.
• 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 Viten.
• 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
• 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.
• 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.

• Aas, Kjetil Schanke; Berntsen, Terje Koren; Boike, Julia; Etzelmuller, Bernd; Kristjansson, Jon Egill; Schuler, Thomas; Stordal, Frode & Westermann, Sebastian (2013). Observed and simulated SEB at Ny-Ålesund, Svalbard.
• Aas, Kjetil Schanke; Berntsen, Terje Koren; Boike, Julia; Etzelmuller, Bernd; Kristjansson, Jon Egill; Schuler, Thomas; Stordal, Frode & Westermann, Sebastian (2013). Observed and simulated surface energy budget at Ny-Ålesund, Svalbard.
• Aas, Kjetil Schanke; Berntsen, Terje Koren; Boike, Julia; Etzelmuller, Bernd; Kristjansson, Jon Egill; Schuler, Thomas; Stordal, Frode & Westermann, Sebastian (2013). Observert og simulert bakke-energibalanse på Svalbard.
• Etzelmuller, Bernd; Westermann, Sebastian; Berntsen, Terje Koren; Dunse, Thorben; Gisnås, Kjersti; Hagen, Jon Ove Methlie; Kristjansson, Jon Egill; Isaksen, Ketil; Vikhamar Schuler, Dagrun; Schuler, Thomas; Stordal, Frode & Aas, Kjetil Schanke (2013). CRYOMET – Concept and Results for Bridging Models Between the Atmosphere and the Terrestrial Cryosphere (Glacier and Permafrost).
• Etzelmuller, Bernd; Westermann, Sebastian; Berntsen, Terje Koren; Gisnås, Kjersti; Hagen, Jon Ove Methlie; Kristjansson, Jon Egill; Schuler, Thomas; Vikhamar Schuler, Dagrun; Stordal, Frode & Aas, Kjetil Schanke (2013). Bridging models for the terrestrial cryosphere and the atmosphere - The CryoMET project.
• Senan, Retish; Orsolini, Yvan & Stordal, Frode (2013). Influence of spring-time Eurasian-Himalayan snow on the evolution of the Indian summer monsoon.
• Westermann, Sebastian; Berntsen, Terje; Etzelmuller, Bernd; Gisnås, Kjersti; Hagen, Jon Ove Methlie; Kristjansson, Jon Egill; Schuler, Thomas & Stordal, Frode (2013). The CryoMet project - combining deterministic and probabilistic downscaling to model snow depth over a wide range of scales.
• Hodnebrog, Øivind; Stordal, Frode; Isaksen, Ivar S A; Gauss, Michael; Berntsen, Terje Koren & Hov, Øystein (2012). Modelling tropospheric ozone production on different scales.
• Westermann, Sebastian; Berntsen, Terje Koren; Etzelmuller, Bernd; Gisnås, Kjersti; Hagen, Jon Ove Methlie; Kristjansson, Jon Egill; Schuler, Thomas & Stordal, Frode (2012). The CryoMET project – combining deterministic and probabilistic downscaling to model snow depth over a wide range of scales.

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