Evaluation of the daylight cycle of model predicted cloud amount and condensed water path over Europe with observations from MSG-SEVIRI

The evaluation of the diurnal cycle of Cloud Amount (CA) and cloud Condensed Water Path (CWP) as predicted by climate models receives relatively little attention, mostly due to the lack of observational data capturing the diurnal cycle of such quantities. The Spinning Enhanced Visible and Infrared Imager (SEVIRI) onboard the geostationary METEOSAT-8 satellite is the first instrument able to provide accurate information on diurnal cycles during daylight hours of cloud properties over land and ocean surfaces. This paper evaluates the daylight cycle of CA and CWP as predicted by the Regional Atmospheric Climate Model version 2 (RACMO), using corresponding SEVIRI retrievals. The study is done for Europe using hourly cloud properties retrievals from SEVIRI during the summer months of May to September 2004.

The results of this study show that SEVIRI retrieved daylight cycles of CA and CWP provide a powerful tool for identifying climate model deficiencies. Over Europe the SEVIRI retrievals of cloud Condensed Water Path comprise for about 80% of liquid water and about 20% of ice water. The daylight cycles of CA and CWP from SEVIRI show large spatial variations in their mean values, time of daily maximum and daytime normalized amplitude. In general, RACMO overestimates CWP by about 30% and underestimates CA by about 20% as compared to SEVIRI. The largest amplitudes are observed in the Mediterranean and Northern Africa. For the greater part of the ocean and coastal areas the time of daily maximum CWP is found during morning, whereas over land this maximum is found after local solar noon. These features are reasonably well captured by RACMO. In the Mediterranean and continental Europe RACMO tends to predict maximum CWP associated with convection to occur about two hours earlier than SEVIRI indicates.