Three-Dimensional Kinematic and Microphysical Evolution of Florida Cumulonimbus. Part I: Spatial Distribution of Updrafts, Downdrafts, and Precipitation

Abstract

This paper is the first in a three-part study that examines the kinematic and microphysical evolution of Florida cumulonimbus and focuses on the convective-to-stratiform transition of the storm. This first paper lays the groundwork for the subsequent papers by defining the problem under study, delineating the setting for the storm, and describing the spatial distribution of updrafts, downdrafts, and precipitation. High-resolution radar data of a typical line of storms associated with the Florida sea breeze is the centerpiece of this study. The high-resolution data reveal details of the internal structure of the squall line that were beyond the resolution of previous squall-line studies. Radar reflectivity filled in between cells at upper levels as the storm evolved. Reflectivity values were only weakly associated with updraft and downdraft magnitude. The updrafts and downdrafts in the storm tended to be irregular in their three-dimensional shape and less than 5 km in horizontal extent. At any given time, updrafts and downdrafts at a variety of strengths were present at all levels throughout the storm. The stronger drafts were usually closer to the leading edge of the storm. Upper-level downdrafts were often located alongside upper-level updrafts. Updrafts tended to drift upward from lower levels and weaken as they aged.