Heights of base and top and thickness of Tropical Clouds

Abstract

ABSTRACT, The heights of base and top of all genera of high and medium clouds and of thunderclouds from 1215 reports by Comet Jet Airliners over India and neighbourhood during the years 1952 and 1953 have been analysed. The mean heights and extremes are given and their seasonal variation discussed. High clouds have their bases most frequently between 30,000 to 45,000 ft with a mean height of36,000 ft much higher than 24,000 ft, a value computed by earlier workers from pilot balloon data. The tops of high clouds may extend up to 5;0,000 ft but most of the high-clouds are only 2000 ft or less in thickness. Medium clouds occur in three separate and distinct -layers with bases at l2000, 20,000 and 25,000 ft. The thickness of there layers decreased with increasing height of base. The tops of medium clouds never extended above 30,000 ft without transformation of the cloud into the cirriform type. The tops of medium clouds are thus much higher than the mean upper level of 20,000 ft, which is given in Cloud Atlases. The mean vertical height of thunderclouds is 40,000 ft which compares with a similar value of 37,000ft for U. S. A. Thunderclouds go up to 50 to 55 thousand feet and are much higher than the presumed 30 to 40 thousand feet. The larger height pf monsoon thunderclouds is attributable to entrainment of air, which is warmer in monsoon than in other seasons:-One out of every ten thunderstorms appears to have a multicellular structure, which is ascribable to frictional drag and horizontal diffusion of momentum.