Climate change projections and stratosphere–troposphere interaction
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Climate change is expected to increase winter rainfall and flooding in many extratropical regions as evaporation and precipitation rates increase, storms become more intense and storm tracks move polewards. Here, we show how changes in stratospheric circulation could play a significant role in future climate change in the extratropics through an additional shift in the tropospheric circulation. This shift in the circulation alters climate change in regional winter rainfall by an amount large enough to significantly alter regional climate change projections. The changes are consistent with changes in stratospheric winds inducing a change in the baroclinic eddy growth rate across the depth of the troposphere. A change in mean wind structure and an equatorward shift of the tropospheric storm tracks relative to models with poor stratospheric resolution allows coupling with surface climate. Using the Atlantic storm track as an example, we show how this can double the predicted increase in extreme winter rainfall over Western and Central Europe compared to other current climate projections.
KeywordsClimate change Europe Stratosphere Storm track
We acknowledge discussions with Jeff Knight, Chris Folland, Doug Smith and Sarah Ineson at the Met Office Hadley Centre while carrying out this work. AAS, DF, NB and SH were supported by the Joint DECC, Defra and MoD Integrated Climate Programme—DECC/Defra (GA01101), MoD (CBC/2B/0417_Annex C5). We also acknowledge funding from the EU-project ENSEMBLES (Contr. No. 505539) and the DFG SPP CAWSES/PROSECCO project. Simulations with model 2 were carried out at the DKRZ in Hamburg, Germany. CCSRNIES computations were completed with the super computer at CGER, NIES and supported by the Global Environmental Research Fund of the Ministry of the Environment of Japan (A-071). 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, U.S. Department of Energy. We acknowledge the Chemistry-Climate Model Validation Activity (CCMVal) for WCRP’s (World Climate Research Programme) SPARC (Stratospheric Processes and their Role in Climate) project for organizing and coordinating the model data analysis activity, and the British Atmospheric Data Centre (BADC) for collecting and archiving the CCMVal model output.
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