Impact of North Atlantic Sea Surface Temperatures on European Summer Climate on Multi-decadal Timescales in Reanalysis and Model Simulations

Abstract:

The observed prominent multidecadal variations in the central to eastern (C-E) European summer temperature are closely related to the Atlantic Multidecadal Variability (AMV). Using the Twentieth Century Reanalysis project version 2 data for the period of 1922 to 2012, we present a mechanism by which the multidecadal variations in the C-E European summer temperature are governed by a quasi-geostrophic (QG) atmospheric response to the AMV related surface heat fluxes. Our results suggest that the QG response causes temperature variations over the C-E European region and it is also responsible for the variations in precipitation over the British Isles and north-western Europe on multidecadal timescales. We further investigate the relation between AMV and European summer climate in the coupled model MPI-ESM and we find that the model is able to simulate a QG response. However, the spatial location of the response differs from the reanalysis which could be due to the differences in the observed and simulated North Atlantic sea surface temperatures (SST). Therefore, further experiments are done to understand the differences in the atmospheric response between the reanalysis and the MPI-ESM through idealized SST-sensitivity experiments with the atmospheric component of MPI-ESM. The atmospheric model is forced by the observed AMV type of SST pattern to better understand the impact of SST biases in the coupled model on the response.