Deep convection in Mediterranean cyclones

.The aim of this paper is to review the problem of deep convection in the Mediterranean basin with special emphasis on phenomena where convection is linked with larger scale structures. It is commonly recognized that cyclonic structures trigger often convective systems in the Mediterranean, and the interaction between such cloud systems and cyclones has not yet been properly investigated. As a major finding of the EU Project MEFFE (Prodi, 2000), a short term climatology of flood events in Europe has shown that the most severe flood episodes occurring in Europe over recent years were caused by cyclonic systems. In particular, two kind of cyclones have been defined, different in their basic structures: Atlantic and Mediterranean (Porcú et.al., 1997a). The first class includes events where the depression is at high latitude (above 50N), presents well defined frontal structures, lasts for several days and produces mainly stratified precipitation. Conversely, Mediterranean cyclones are mainly generated in Southern Europe as a perturbation of a polar front, are usually short lived (about one day) and always develop deep convection. While the first class has been studied extensively and conceptual models describing the main features have been developed and are widely used in the operational forecasting environment (see Browning (1982) for a summary), the study of the Mediterranean class is still at an early stage. Isolated and organized convection has been intensively studied in Europe over the last decade, and it has been seen that Europen convective systems show new features with respect to the well known systems in the U.S. and tropics. Nevertheless, only recently has the close connection between cyclogenesis and deep convection been pointed out. Since such cloud systems develop mainly over the sea, it seems that the extensive use of ground radar must be excluded for such studies: a space-view approach is needed. A review of satellite techniques for studying convection is presented, and some new results of their application to Mediterranean systems are summarized. The structure of this paper is as follows: Section 2 gives an overview of the research activity on convection in Europe; Section 3 outlines some techniques used for the study of convection from space; Section 4 presents a kind of classification of convective systems occurring in the Mediterranean with a possible interpretation of some mechanisms involved.