Measurements of Precipitation Particles in Warm Cumuli over Southeast Texas

Abstract

Precipitation particles >250 ? were sampled in the upper regions of warm cumuli over southeast Texas using a foil-belt particle sampler. It was found that relatively high concentrations of drops can occur. Concentrations exceeding 1000 m?3 were found in nearly 25% of the clouds. Drop sizes 1 mm in diameter were found fairly often, and 2-mm drops were occasionally sampled. The effect of cloud height on the precipitation characteristics was found to be quite pronounced. Higher concentrations and broader distributions generally were found in the tallest clouds. The height of clouds plays a more important role in determining drop concentration and size distribution range than do updrafts or downdrafts. In a comparison between concentration of precipitation particles and average cloud water content (CWCm), it was found that large quantities of drops were associated with low CWCm. Conversely, large values of CWCm were associated with small numbers of drops >250 ? in diameter. The 1968 clouds generally contained much higher concentrations of drops and had broader distributions of drop sizes than did the 1969 clouds. Smaller clouds investigated during 1968 were nearly as proficient in developing large drops as much taller clouds studied during 1969. The 1968 clouds seemed to have precipitation particle characteristics that were similar to trade-wind cumuli investigated by Brown and Braham, while the drop characteristics of the 1969 clouds were more nearly like the cumulus congestus studied in Missouri, also by Brown and Braham.