Aircraft observations of large raindrops in warm, shallow, convective clouds

Abstract

Raindrop size distributions have been obtained using airborne optical array probes during the 1985 Joint Hawaiian Warm Rain Project near Hilo. Drops often extended to 4 or 5 mm diameter, and on one occasion even reached 8 mm—much larger than had been previously reported. Large raindrops were detected frequently enough to indicate that they may be a regular feature of tropic clouds which are rather shallow but convectively active. The preliminary analysis of the data, involving some simple cloud physics calculations, indicates that the conditions in these clouds are well suited for the growth and survival of large raindrops. The presence of large raindrops suggests that a number of wide‐spread views on the formation and evolution of warm rain should be altered, and that earlier data obtained in the orographic clouds of Hawaii should not be extrapolated uncritically to all types of warm rain.