Three-Dimensional Kinematic and Microphysical Evolution of Florida Cumulonimbus. Part II: Frequency Distributions of Vertical Velocity, Reflectivity, and Differential Reflectivity

Abstract

High-resolution radar data collected in Florida during the Convection and Precipitation/Electrification Experiment are used to elucidate the microphysical and kinematic processes occurring during the transition of a multicellular storm from convective to stratiform stages. A statistical technique is employed to examine the evolving properties of the ensemble small-scale variability of radar reflectivity, vertical velocity, and differential reflectivity over the entire storm. Differential radar reflectivity data indicate that the precipitation at upper levels was nearly glaciated early in the storm's lifetime. Dual-Doppler radar data show that throughout the storm's lifetime both updrafts and down-drafts were present at all altitudes and that most of the volume of the radar echo contained vertical velocities incapable of supporting precipitation-size particles. Thus, the ensemble microphysical properties of the storm were increasingly dominated by particles falling in an environment of weak vertical velocity, and the radar reflectivity began to take on a statistically stratiform character during the early stages of the storm. This stratiform structure became more distinct as the storm aged. Two dynamically distinct downdrafts were indicated. Lower-level downdrafts were associated with precipitation. Upper-level downdrafts were dynamically associated with the stronger upper-level updrafts and were likely primarily a consequence of the pressure gradient forces required to maintain mass continuity in the presence of buoyant updrafts.