A Diagnostic Study of a Non-Deepening Disturbance in the Caribbean Sea

Abstract

This paper discusses the results obtained from a study of a non-deepening disturbance which developed and dissipated in the Caribbean Sea. Careful analyses Of the temperature moisture, and wind fields Were performed at six levels for a two-day, period while the disturbance was dissipating. The data were used to compute vertical motions from a nonlinear balance model for the purpose of diagnosing the reasons for decay of the disturbance. The vertical motions that were derived from the diagnostic computations compared favorably with the synoptic-scale cloud distribution. The results suggested that the presence of clouds within the disturbance on the first day was attributed to 1) frictionally induced ascending motions in the lower troposphere where there were large values of specific humidity, 2) the Laplacian of thermal advection which produced rising motions in the lower and upper troposphere where there were weak, though significant, temperature gradients, and 3) ascending motions in the upper troposphere which were contributed by convective latent heat release. When the disturbance decayed on the second day, the diagnostic computations produced weak subsidence in the lower troposphere by the synoptic-scale frictional and thermal effects. As a consequence, the low-level moisture convergence was suppressed and the latent heat release was negligible. The results point out the importance of synoptic-scale circulation and convection as being cooperative mechanisms for extensive cloud formation.