Resolution Dependence of Precipitation and Deep Convection over the Gulf Stream

The influence of horizontal resolution of an Atmospheric Global Circulation Model on the simulation of wintertime precipitation and atmospheric deep convection above the North Atlantic and especially the Gulf Stream region is
studied. It is shown that mean precipitation increases with increasing resolution. Via an analysis of the position of the jetstream and other
features of the large scale circulation, it is suggested that the differences in mean precipitation in the GCM are not caused by differences in large scale circulation, but mainly by local phenomena. Increasing resolution in the GCM especially leads to more extreme precipitation.
An assessment whether the increase in extreme precipitation deteriorates or improves model performance appears problematic as it depends on which observational product is used. Furthermore, 10m wind convergence has been analyzed and it is shown that the higher resolution GCM shows more extreme wind convergence events and corresponds better to wind convergence derived from observations. Additionally, the number of deep convection events above the Gulf Stream increases with resolution in the GCM, enhancing the communication of Sea Surface Temperatures up to the troposphere.