Resolution dependence of extreme precipitation and deep convection over the Gulf Stream

Modeled wintertime precipitation over the Atlantic Gulf Stream region is shown to be sensitive to the horizontal resolution of the driving Global Circulation Model (GCM). By contrasting simulations with the EC-Earth GCM over a range of horizontal resolutions (T159, T319, T799), it is shown that especially the precipitation extremes become more populated if resolution is higher. Higher resolution also appears to strengthen the communication from the sea surface toward the troposphere. With increasing resolution, deep convection over the Gulf Stream region, diagnosed via wind-convergence and vertical motion, occurs more frequently and the former is in better agreement with observations. Likewise the frequency increase of the precipitation extremes over the region for increasing resolution makes them agree better with observations, despite large natural variability and discrepancies between different observational sources.