Hydrometeor structure of a composite monsoon depression using the TRMM radar

Abstract

This paper addresses the use of a satellite-based radar for obtaining the composite structure(from several monsoon depressions) of the distribution of precipitation elements in the horizontaland the vertical. This composting is based on the use of a simple elliptical layout ofcoordinates along the major and minor axes of each storm as it passed over north central India.This satellite, called the Tropical Rainfall Measuring Mission (TRMM), carries onboard amicrowave instrument known as the Precipitation Radar (PR). The vertical structure ofhydrometeors provided by the radar is somewhat of the same quality as the ground-basedDoppler radar units. The PR could identify many features such as the melting layers, height ofconvection, extent of anvils and types of precipitation over different sections of the compositedmonsoon depression. Furthermore, the asymmetric nature of surface rainfall that intensifiesaround the composited monsoon depression has also been mapped, which could provide severalmore details than was possible from other satellite-based estimates. It is found that the mostintense precipitation occurs in the south-southwest region of the monsoon depression. Thepreponderance of stratiform rain and the coverage of fewer deep convective elements, especiallyover the orographic upslope region, are some other noticeable features obtained using theTRMM PR. The stratiform rain was noted to arise where the melting layers (in the radarreflectivity signatures) were located near 5 km. In those few occasions where tall rain cloudswere discernible, the cloud tops were seen to extend all the way from 12 to 15 km. Rainfallamounts across the composite monsoon depression range from 10 to 100 mm d-1. The 3—4 dpassage time of one of those disturbances resulted in local rainfall totals of the order of 200—300 mm d-1.