Resolution Dependence of European Precipitation in a State-of-the-Art Atmospheric General Circulation Model

In this study, the authors investigate the effect of GCM spatial resolution on modeled precipitation over Europe. The objectives of the analysis are to determine whether climate models have sufficient spatial resolution to have an accurate representation of the storm tracks that affect precipitation. They investigate if there is a significant statistical difference in modeled precipitation between a medium-resolution (~112-km horizontal resolution) and a high-resolution (~25-km horizontal resolution) version of a state-of-the-art AGCM (EC-EARTH), if either model resolution gives a better representation of precipitation in the current climate, and what processes are responsible for the differences in modeled precipitation. The authors find that the high-resolution model gives a more accurate representation of northern and central European winter precipitation. The medium-resolution model has a larger positive bias in precipitation in most of the northern half of Europe. Storm tracks are better simulated in the high-resolution model, providing for a more accurate horizontal moisture transport and moisture convergence. Using a decomposition of the precipitation difference between the medium- and high-resolution model in a part related and a part unrelated to a difference in the distribution of vertical atmospheric velocity, the authors find that the smaller precipitation bias in central and northern Europe is largely unrelated to a difference in vertical velocity distribution. The smaller precipitation amount in these areas is in agreement with less moisture transport over this area in the high-resolution model. In areas with orography the change in vertical velocity distribution is found to be more important.