Mesoscale Events within a GATE Tropical Depression

Abstract

A tropical depression which intensified quite close to Dakar on 15 July 1974 was one of the strongest weather systems investigated during the GATE field program. A coordinated data set, consisting of satellite, radar, dropwindsonde and ship data, is analyzed to define both synoptic-scale and smaller scale event for a period of about 6 h. The wind fields and precipitation fields are presented in some detail for the time with the best data coverage, and the changes that took place for several hours on either side of that time are discussed. Some mesoscale events of considerable strength occurred. Mesoscale organization of deep convection, accompanied by strong mesoscale convergence at low levels, preceded mesoscale cyclogenesis. There was a marked mesoscale cyclonic center bordered in part by deep convective clouds that resembled the eye structure of a tropical cyclone in some respects. The large-scale thermodynamic stratification is noted to have been an important control on the distribution of deep convection within the tropical depression and on the eventual disappearance of deep convection.