Trends in winter circulation over the British Isles and central Europe in twenty-first century projections by 25 CMIP5 GCMs

Abstract

Winter midlatitude atmospheric circulation has been extensively studied for its tight link to surface weather, and automated circulation classifications have often been used to this end. Here, eight such classifications are applied to daily sea level pressure patterns simulated by an ensemble of CMIP5 GCMs twenty-first century projections for the British Isles and central Europe in order to robustly estimate future changes in frequency, persistence, and strength of synoptic-scale circulation there. All methods are able to identify present-day biases of models reported before, such as an overestimated occurrence of zonal flow and underestimation of anticyclonic conditions and easterly advection, although the strength of these biases varies among the methods. In future, models show that the zonal flow will become more frequent while the strength of the mean flow is not projected to change. Over the British Isles, the models that better simulate the latitude of zonal flow over the historical period indicate a slight equatorward shift of westerlies in their projections, while the poleward expansion of circulation—expected in future at global scale—is apparent in those models that have large errors. Over central Europe, some classifications indicate an increase in persistence and especially in frequency of anticyclonic types, which is, however, shown to be rather an artifact of some methods than a real feature. On the other hand, the easterly flow is robustly projected to become markedly weaker in central Europe, which we hypothesize might be an important factor contributing to the projected decrease of cold extremes there.

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Acknowledgements

The work was funded by the Grant Agency of Charles University, Project 188214. We acknowledge all modeling groups for providing their GCM data and the Earth System Grid-Center for Enabling Technologies (ESG-CET) for enabling access to it. We thank NOAA/OAR/ESRL PSD, Boulder, Colorado, for the NCEP–NCAR reanalysis and Twentieth Century Reanalysis, version 2; ECMWF for ERA-40 and ERA-20C; and JMA for JRA-55. All developers of the COST733 software are greatly acknowledged, and so is the Institute of Geography, University of Augsburg, Germany, for maintaining the software and providing access to it.

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Stryhal, J., Huth, R. Trends in winter circulation over the British Isles and central Europe in twenty-first century projections by 25 CMIP5 GCMs. Clim Dyn 52, 1063–1075 (2019). https://doi.org/10.1007/s00382-018-4178-3

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Keywords

  • Global climate models
  • CMIP5
  • Projections
  • Atmospheric circulation
  • Circulation classifications