A numerical study using the Canadian Regional Climate Model for the PIDCAP period

Simulations of summertime conditions over the BALTEX region using the Canadian Regional Climate Model (CRCM) are compared with observations for the PIDCAP period. A systematic cold bias of the surface temperature was found in a reference simulation made with a version of the CRCM which uses the physical processes package of the third generation global climate model of the Canadian Centre for Climate Modeling and Analysis. This cold bias is found to be due to excessive cloud near the surface. Revision of the cloud scheme, which was originally designed for use in conjunction with relatively coarse resolution of the AGCM, results in a reduction of the cloud cover, improved net radiative flux at the surface and substantial reduction of the cold bias. An associated result is that the lower atmosphere becomes more conditionally unstable which increases the number of convective events. Nevertheless the incidence of convective precipitation events remains unrealistically low.