Factors shaping the global warming atmospheric response in the North Atlantic Sector

Noel S Keenlyside, Geophysical Institute Bergen, Bergen, Norway, Ralf Hand, Max Planck Institute for Meteorology, Hamburg, Germany, Nour-Eddine Omrani, University of Bergen and Bjerknes Centre, Geophysical Institute, Bergen, Norway, Juergen Bader, Max Planck Institute for Meteorology, The Land in the Earth System, Hamburg, Germany and Richard John Greatbatch, GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany
Abstract:
There are great uncertainties in future projections of climate at a regional scale. Better understanding of local feedbacks, which can play a dominant role in shaping regional climate change, may help to reduce these uncertainties. Here we investigate the contributions from local and remote factors in climate change in the North Atlantic sector, through sets of experiments with the MPI climate model and its atmospheric component ECHAM. We focus on the boreal winter.

Our results show (1) that the local sea surface temperature (SST) changes, which are robust feature of CMIP, focus the atmospheric circulation and precipitation over the North Atlantic Ocean; (2) Large circulation changes are not forced by the local SST changes, and instead (3) they are mostly controlled by tropical SST. The mechanisms for each of these responses has been investigated in detail, and we have identified the role of tropospheric static stability changes in driving the extra-tropical wave response, and local SST gradients in focusing the precipitation changes over the Gulf Stream and its extension. The potential role of model resolution will be discussed.

Back to: Midlatitude Climate Dynamics and the Role of the Ocean II