Evaluation of the diurnal cycle of model predicted cloud liquid water path with MSG-SEVIRI observations

The evaluation of diurnal cycles of cloud Liquid Water path (LWP) in climate models receives relatively little attention. This is partly due to the lack of reference data to evaluate these cycles. The Spinning Enhanced Visible and Infrared Imager (SEVIRI) onboard METEOSAT-8 is the first instrument with the potential to provide accurate information on diurnal cycles of LWP over land and ocean surfaces. This paper evaluates diurnal cycles of LWP in the Regional Atmospheric Climate Model (RACMO) over Europe, using corresponding SEVIRI retrievals. The results show that diurnal cycles of LWP from SEVIRI show large spatial variations in their mean values, time of daytime maximum and daytime normalized amplitude. Over Europe RACMO overestimates LWP by about 75% as compared to SEVIRI. In general, the SEVIRI observed spatial variations in normalized amplitude and daytime maximum of LWP are well captured by RACMO. The best agreement between SEVIRI and RACMO is found over Ocean. Most differences are found in Mediterranean and Continental climates, where RACMO tends to predict maximum convection about two hours earlier than SEVIRI. Moreover, RACMO predicts different diurnal cycles than SEVIRI in regions with frequent changes in surface type or weather conditions. In conclusion, the results of this study show that SEVIRI retrieved diurnal cycles of LWP provide a powerful tool for identifying climate model deficiencies.