Impact of a projected future Arctic Sea Ice reduction on extratropical storminess and the NAO
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The impact of a reduced Arctic sea ice cover on wintertime extratropical storminess is investigated by conducting atmospheric general circulation model (AGCM) experiments. The AGCM ECHAM5 is forced by the present and a projected future seasonal cycle of Arctic sea ice. In the experiment with projected sea-ice concentrations significant reductions in storminess were found during December and January in both midlatitudes and towards the Arctic. However, a substantially larger reduction in extratropical storminess was found in March, despite a smaller change in surface energy fluxes in March than in the other winter months. The projected decrease in storminess is also related to the negative phase of the North Atlantic Oscillation (NAO). The March response is consistent with a forcing from transient and quasi-stationary eddies associated with negative NAO events. The greater sensitivity to sea-ice anomalies in late winter sets this study apart from earlier ones.
KeywordsSea-ice NAO Storminess Climate change Seasonality AGCM
We thank Nils Gunnar Kvamstø, Gudrun Magnusdottir and Justin Wettstein for insightful discussions. We thank the Max-Planck-Institute for Meteorology for providing and supporting the ECHAM5 model. The UK Meteorological Office and Hadley Centre is acknowledged for providing the HadISST 1.1—global sea-ice coverage and SST—dataset. We acknowledge the modeling groups, the Program for Climate Model Diagnosis and Intercomparison (PCMDI) and the WCRP’s Working Group on Coupled Modelling (WGCM) for their roles in making available the WCRP CMIP3 multi-model dataset. Support of this dataset is provided by the Office of Science, US Department of Energy. This work was supported by the COMPAS and NorClim projects funded by the research council of Norway. The model runs have been performed at the Norwegian Metacenter For Computational Science (NOTUR) in Trondheim.