A tropical squall line observed during the COPT 81 experiment in West Africa: Part 1: kinematic structure inferred from dual- Doppler radar data.

Abstract

At the observation time, the squall line was in a mature stage. The general characteristics of the squall line are found to be very similar to those of tropical squall line observed during previous experiments such as VHIMEX or GATE: a large cloud system composed of an organized convective line ahead of an extensive trailing anvil cloud (stratiform rain), fast motion and long-lasting structure and a well-marked gust front signature at ground level. However, detailed aspects of the 3D wind field reveal significant differences. The rear-to-front flow is observed in a deep layer 3km thick. From mass transport estimation, it is found that convective and mesoscale downdrafts accounted for 40 and 60% of the deep rear-to-front flow, respectively. Through this mechanism, the mesoscale downdraft plays an important role in the generation of convective updrafts along the leading gust front. In face, part of the mesoscale downdraft air spreads forward and overlies the outflow generated in the surface layer by the convective-scale downdrafts. This results from processes occurring in the trailing anvil.-from Authors