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  • 1
    Publication Date: 2021-01-08
    Description: The ability of state‐of‐the‐art regional climate models to simulate cyclone activity in the Arctic is assessed based on an ensemble of 13 simulations from 11 models from the Arctic‐CORDEX initiative. Some models employ large‐scale spectral nudging techniques. Cyclone characteristics simulated by the ensemble are compared with the results forced by four reanalyses (ERA‐Interim, National Centers for Environmental Prediction‐Climate Forecast System Reanalysis, National Aeronautics and Space Administration‐Modern‐Era Retrospective analysis for Research and Applications Version 2, and Japan Meteorological Agency‐Japanese 55‐year reanalysis) in winter and summer for 1981–2010 period. In addition, we compare cyclone statistics between ERA‐Interim and the Arctic System Reanalysis reanalyses for 2000–2010. Biases in cyclone frequency, intensity, and size over the Arctic are also quantified. Variations in cyclone frequency across the models are partly attributed to the differences in cyclone frequency over land. The variations across the models are largest for small and shallow cyclones for both seasons. A connection between biases in the zonal wind at 200 hPa and cyclone characteristics is found for both seasons. Most models underestimate zonal wind speed in both seasons, which likely leads to underestimation of cyclone mean depth and deep cyclone frequency in the Arctic. In general, the regional climate models are able to represent the spatial distribution of cyclone characteristics in the Arctic but models that employ large‐scale spectral nudging show a better agreement with ERA‐Interim reanalysis than the rest of the models. Trends also exhibit the benefits of nudging. Models with spectral nudging are able to reproduce the cyclone trends, whereas most of the nonnudged models fail to do so. However, the cyclone characteristics and trends are sensitive to the choice of nudged variables.
    Type: Article , PeerReviewed
    Format: text
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  • 2
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    WILEY-BLACKWELL PUBLISHING
    In:  EPIC3Tellus Series A-Dynamic Meteorology and Oceanography, WILEY-BLACKWELL PUBLISHING, 65, pp. 19375, ISSN: 0280-6495
    Publication Date: 2019-07-17
    Description: The stratospheric response to the observed Arctic sea ice retreat is analysed based on European Centre for Medium-Range Weather Forecast (ECMWF) Re-Analysis Interim (ERA-Interim) atmospheric data from 1979-2012. It is shown that changes in August/September sea ice concentration impact on tropospheric and stratospheric geopotential heights in the following winter. During low ice phases a negative tropospheric Arctic Oscillation pattern is found, which is connected to a weakened stratospheric polar vortex and warmer stratospheric temperatures. Furthermore, the analysis reveals enhanced upward EP fluxes due to planetary waves for low ice conditions. Strong stratospheric anomalies in the Atlantic/European region are associated with a weaker polar vortex. Low ice periods are connected with additional tropospheric wave energy excitation in the Pacific/North America region and influence the stratosphere through three-dimensional planetary wave propagation.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Format: application/pdf
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  • 3
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    WILEY-BLACKWELL PUBLISHING
    In:  EPIC3Tellus Series A-Dynamic Meteorology and Oceanography, WILEY-BLACKWELL PUBLISHING, 64, ISSN: 0280-6495
    Publication Date: 2019-07-17
    Description: The impact of anomalous fall Arctic sea ice concentrations (SICs) on atmospheric patterns in the following winter is revisited by analysing results for two time periods: the most recent, satellite-era period (1979–2010) and a longer time-period (1950–2010). On the basis of September SICs for each time-period, an index was constructed which was used to identify anomalous high/low SIC years for both the original, as well as for the linearly detrended sea ice index. Identified years were then used to derive composites for the following winter's monthly atmospheric variables. Mid-troposphere geopotential height composites for winter months are in general reminiscent of the North Atlantic Oscillation pattern with high latitude maximum shifted towards the Barents Sea. Also, lower troposphere temperatures indicate the presence of cooler conditions over the continents during low SIC years. However, differences in the composite patterns are significant only for areas with limited spatial extent. While suggested pathways in previously published studies seem reasonable, our results show that these findings are not yet robust enough from a statistical significance perspective. More data (e.g. provided by longer, climate-quality reanalysis datasets) are needed before conclusions of impacts and feedbacks can be drawn with certainty.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , peerRev
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  • 4
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    WILEY-BLACKWELL PUBLISHING
    In:  EPIC3Tellus Series A-Dynamic Meteorology and Oceanography, WILEY-BLACKWELL PUBLISHING, 64(19777), pp. 1-27, ISSN: 0280-6495
    Publication Date: 2019-07-17
    Description: This article evaluates the ability of state-of-the-art climate models to reproduce the low-frequency variability of the mid-tropospheric winter flow of the Northern Hemisphere in terms of atmospheric teleconnection patterns. Therefore, multi-model simulations for present-day conditions, performed for the 4th assessment report of the Intergovernmental Panel on Climate Change, have been analysed and compared with re-analysis data sets. The spatial patterns of atmospheric teleconnections are reproduced reasonably by most of the models. The comparison of coupled with atmosphere-only runs confirmed that a better representation of the forcing by sea surface temperatures has the potential to slightly improve the representation of only wave train-like patterns. Due to internally generated climate variability, the models are not able to reproduce the observed temporal behaviour. Insights into the dynamical reasons for the limited skill of climate models in reproducing teleconnections have been obtained by studying the relation between major teleconnections and zonal wind variability patterns. About half of the models are able to reproduce the observed relationship. For these cases, the quality of simulated teleconnection patterns is largely determined by the quality of zonal wind variability patterns. Therefore, improvements of simulated eddy-mean flow interaction have the potential to improve the atmospheric teleconnections.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Format: application/pdf
    Format: application/pdf
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