Vertical structure and evolution of a supercell storm: observations using VHF radar

S. Abhilasha* & K. Mohankumara a Department of Atmospheric Sciences , Cochin University of Science and Technology , Finearts Avenue, Cochin 682 016 , India * E-mail: abhimets@yahoo.com An attempt has been made in the present study to characterise the vertical kinematic structure of a supercell storm during its different phases of development. The present study utilises the high time and height resolution 53 MHz VHF radar observations at Gadanki (13.5° N, 79.2° E), India. A supercell storm passed over the radar site during 17–18 October, 2002, and has been sampled during its mature to dissipating stages of convective activity. The time height variation of the radar reflectivity in terms of signal to noise ratio (SNR) and spectral width along with vertical velocity have been used to separate two distinct phases of the convective activity associated with the supercell storm. The mature phase of the storm is characterised by enhancement of high value of SNR from the lower troposphere up to the height of the tropopause. During this period, the vertical velocity in the middle troposphere is of the order of 8 to 10 ms−1. The dissipating stage is characterised by diminished structure of SNR in the middle and upper troposphere. During this period, downwards motion is present in the troposphere. Oscillatory nature of the vertical velocity is found in the upper tropospheric/lower stratospheric (UT/LS) region and shows signatures of short period gravity waves. The power spectral and wavelet analysis of the vertical wind perturbations shows signatures of high frequency oscillations of periodicity between 8–30 min. These high frequency waves are possibly owing to the oscillating updrafts and downdrafts impinging on the tropopause owing to penetrative convection.