An analysis of a developing and non-developing disturbance during the predict experiment

Abstract

An analysis is presented of the failed re-development of ex-Gaston and the development of Karl during the 2010 PREDICT field campaign based on the European Centre for Medium RangeWeather Forecast (ECMWF) analyses. This study analyzes the flow kine-matics and dynamics of ex-Gaston to investigate the role of dry, environmental air in the failed redevelopment. The findings support the hypothesis that entrained, dry air near 600 hPa thwarted convective updraughts and vertical mass flux, which in turn leads to a reduction in vorticity and a compromised pouch at these middle levels. A compromised pouch allows further intrusion of dry air and inhibits vorticity amplification. This study supports recent work investigating the role of dry air in moist convection during tropical cyclogenesis. The circulation and vorticity dynamics of Karl are used to describe the system-scale spin-up within the marsupial paradigm frame-work. The circulation tendency shows that Karl underwent periods of spin-up and spin-down until its eventual development on 14 September. These spin-up and spin-down episodes correspond with the cycle of convective activity in the Caribbean. The development process is concomitant with recent work describing the genesis and intensification process in developing tropical cyclones.