Duration of Convective Events Related to Visible Cloud, Convergence, Radar and Rain Gage Parameters in South Florida

Abstract

The time interval between initiation of surface convergence and the subsequent response of visible cloud growth to this convergence was examined for nine cases of convection that occurred over the FACE 1973 and 1975 mesonetworks in south Florida. Clouds ranged in size from small echoes with a few towers to merged lines or large clusters of towers, but they met a series of observational criteria that specified them as belonging to a similar set of clouds, and were not representative of the entire range of clouds in the area. Visible clouds first formed 10 to 55 min after the associated surface convergence began, and grew rapidly upward 20 to 100 min after convergence started. This highly variable response could be understood better by taking into account the duration of the cloud, which is defined as the time from first surface convergence to complete dissipation. The same nine cases were examined as were chosen initially for the visible cloud study. When duration was considered, first visible cloud response occurred at an average of 15% through the cloud duration, and rapid upward cloud growth at 36%. Other parameters derived from divergence, radar- and gage-measured rainfall also tended to cluster within specific portions of the total duration of the cloud. The data for each event for the nine clouds are presented and described in terms of the cloud duration.