Towards climate simulations at cloud-resolving scales

This study explores the potential added-value of applying cloud-resolving resolution to climate simulations. A month-long (July 2006) integration is performed with the CCLM on a convection-resolving grid of 2.2-km (0.02°) mesh size spanning the whole Alpine region. The initial and lateral boundary conditions stem from a coarser-resolution 25-km (0.22°) CCLM integration. Comparison to observations indicates that the cloud-resolving simulation is able to capture the overall precipitation distribution and evolution. With respect to its driving lower-resolution integration, the cloud-resolving resolution yields a more accurate spatial localization of the precipitation maxima, reduces the cold bias, and especially reproduces a better timing of the convective diurnal cycle. The explicit resolution delays the onset of convective precipitation by about 2 h, shifts the time of peak precipitation by a similar period, and slows down the decay of convective activity in the afternoon. In return, the integration shows a tendency to underestimate the afternoon convective rainfalls, particularly under weak synoptic and/or orographic forcing. This latter effect might be improved by modifying the treatment of subgrid-scale clouds in the model.