Responses of tropical deep convective precipitation systems and their associated convective and stratiform regions to the large-scale forcing

Responses of convective and stratiform rainfall to large-scale forcing in the tropical deep convective regime are investigated by analysing data front a two-dimensional cloud-resolving Model simulation. The model is forced by large-scale vertical velocity. zonal wind, horizontal advection, and sea-surface temperature observed and derived from TOGA COARE. The imposed large-scale vertical velocity shows that the ascending motion averaged front 22-27 December 1992 is significantly stronger than that averaged from 3-8 January 1993. Thus, the periods of 22-27 December 1992 and 3-8 January 1993 are. respectively. identified as strong-forcing (SF) and weak-forcing (WF) phases. Although the convective rain rates are similar in the two phases. startiform rain rate is larger in the SF phase than in the WF phase. which leads to larger time and spatial mean surface rain rate in the SF phase. Similar rates of water vapour convergence and vapour condensation and collection of cloud water by rain over water-hydrometer-dominated convective regions are responsible for similar convective rain rates in the two phases. Water vapour divergence is larger in the WF phase than in the SF phase. which causes smaller vapour condensation and deposition rates in the WF phase. As a result, the collection rate of cloud water by rain and the melting rate of graupel to rain are smaller in the WF phase than in the SF phase, which accounts for the smaller startiform rain rate in the WF phase. Copyright (C) 2008 Royal Meterological Society