Cloud Top Height Variability of Strong Convective Cells

Abstract

Cloud top height variability of cloud domes above the cirrostratus anvil was investigated for two severe local storm occurrences over Texas on 12 and 13 May 1972. From a Lear Jet at 14 km, side-looking photographs were taken at distances of 50 to 200 km from the thunderstorm clusters every 30 sec for periods up to 1.5 hr. Ground based WSR-57 radar measurements were used to establish the positions of the cells and airplane positions were recorded every minute. Twenty-three domes were monitored and the average maximum height was 1.6 km above the anvil. It was estimated that a dome would take a maximum of about 6 min to grow from the anvil level to peak altitude based on measurements over the last 2 min of the growth period when the upward vertical velocity averaged 4 m sec?1. The extreme vertical growth rate was 27 m sec?1 for a 30-sec period. This vertical growth rate compared with a range of 11.4?19.4 m sec?1 determined from a method of estimating vertical motions based on laboratory measurements. Average dome collapse was at the same rate as the average ascent for the first 90 sec after the maximum altitude was reached. With a slightly smaller sample it was determined that the domes grew both horizontally and vertically until the maximum cloud top altitude was attained. Then, for the next 60 sec, horizontal growth continued while the vertical height was decreasing.