Aircraft Traverses in a Growing Mountain Cumulus Cloud

Abstract

During a one-hour interval while a mountain cumulus cloud system was developing into a cumulonimbus, in a light wind condition over an isolated peak, a series of 17 traverses was made through the clouds by an instrumented aircraft. Time-lapse cloud photographs and radar records were available for the same sequence. The observations are presented and briefly analysed. The cloud towers had active lives which started out at two minutes and increased to more than 30 minutes as the clouds developed. Deep in the cloud the air-craft was able to find the same updrafts on consecutive traverses for from 7 to 18 minutes. The updrafts observed by the aircraft within the cloud had vertical velocities two to three times as great as the maximum rate of rise of the towers. The length of the vertical flow of air past the flight level for a typical updraft was 18,000 ft or more, while the diameter of the updraft was only 3,000 ft. The towers broadened somewhat as the cloud developed and became rapidly broader just as the first radar echoes occurred. The gross features of the convective cells were in general agreement with the ?starting plume? treated by J. S. Turner.