A Radar Study of Convective Cells in Mesoscale Systems in GATE. Part I: Vertical Profile Statistics and Comparison with Hurricanes

Abstract

This is Part I of a two-paper describing the structure of the vertical profile of radar reflectivity in convective cells which are of part of mesoscale convective systems in GATE. Earlier work has established that characteristic mean vertical velocities in such convective clouds in GATE were rather weak, <3–5 m s−1. The microphysical implications of the weak updrafts have been proposed to include the rarity of large particles above the freezing level. As a working hypothesis for these papers it is proposed that cells with weak updrafts have characteristic vertical reflectivity profiles exhibiting modest reflectivities at low levels, and decreasing rapidly with height above the freezing level. Vertical radar reflectivity profiles are compiled from 296 convective cells having at least 40 dBZ surface reflectivity, and it is found that the profiles are consistent with the above reasoning. The, mean profile is of modest strength—45 dBZ echo at the surface and a 20 dBZ echo top of 8.2 km, and the reflectivity decreases rapidly with height above the freezing level. Statistics of surface reflectivity, echo top, and height of the maximum echo aloft all lend support to the above picture of the GATE cell. The GATE radar profiles are similar to mature hurricane radar profiles, consistent with their updraft velocities being weak as well. In contrast the GATE profiles are markedly weaker than profiles from continental thunderstorm cells, consistent with the much higher vertical velocities in the continental cells.