Behavior of the Wind Field in the Vicinity of a Cloud Cluster in the Intertropical Convergence Zone

Abstract

The 5 September 1974 double cloud cluster formed in a large-scale wind field characterized by convergence of the trade winds along a line of confluence at the surface, a synoptic-scale wave in the mid-tropospheric easterlies and a difluent easterly flow near the tropopause. As the double cloud cluster matured, a closed center of cyclonic circulation formed in the surface wind field. After a time lag of several hours, the 700 mb flow developed a closed cyclonic circulation with a distinct double structure and the 200 mb flow was perturbed by a center of anticyclonic outflow. Both occurred over the region occupied by the dissipating cloud cluster. As the cloud cluster was dissipating, these wind perturbations on the scale of the cloud cluster weakened at all three levels. The wind perturbations followed a pattern similar to those produced by the 4?5 September 1974 squall-line system, suggesting that different types of cloud clusters have qualitatively similar feedbacks to their large-scale environment.