Features of thermals in stable wake and neutral stratifications in the disturbed monsoon boundary layer

Abstract

Thermals, detined as humidity excesses, seem to exhibit distinct features in the disturbed Indian Monsoon Boundary Layer (BL) depending on whether they occur in the stable wake regions, called S in this study, oftropical squalls, or in the neutral regions of the advancing squalls, called N. The stable S region developed weak but gradually increasing ascending motion in the BL while the N region showed strong upward motion at the top of the surface layer (85 m) decreasing steadily thereafter. Similar differences also appear in the other mean thermal fields such as temperature and humidity.The present study agrees with that of Lenschow and Stephens in that there is an increase of thermal cover (area covered by thermals) with height. Our study points out additionally that this happens only within the stable wake region. In the neutral region, the thermal cover is fairly constant.It appears that thermal parameters such as vertical velocity are good indicators of the atmospheric BL structure.