SIMULATION OF A LONG-LIVED MESO-BETA SCALE CONVECTIVE SYSTEM OVER THEMEDITERRANEAN COAST OF SPAIN .2. SENSITIVITY TO EXTERNAL FORCINGS

The numerical simulation of a long-lived, stationary mesoscale convect ive system (MCS) already described in a previous paper (Fernandez et a l., 1995) is analyzed in greater detail. The influence of various exte rnal forcings, such as sea surface temperature, local orography or ter rain roughness, upon the characteristics of the system is studied. Thi s analysis makes it possible not only to identify the most important f actors, but also to deduce the importance of some other internal forci ngs and to propose explanations for some dynamic features of the syste m that were difficult to understand. Hence, the sensitivity test metho dology applied seems to be a useful tool to clarify the complex dynami cs of some moist convective events. In the modelled MCS, sea surface t emperature and orography are identified as key factors. The results al so indicate that the upstream triggering of convection provoked by an orographic blocking effect is the main cause of the development of the system, while upslope triggering plays a secondary role.