Characteristics of high‐frequency gravity waves generated by tropical deep convection: Case studies

Abstract

High‐frequency gravity waves generated by tropical deep convection play a major role in shaping the general circulation of the middle atmosphere. Special experiments were conducted to capture two convective events on 16 May and 5 June 2006 using VHF radar located at Gadanki (13.5°N, 79.2°E), a tropical Indian station. Control day observations were also made for necessary comparisons. Background wind and temperature information was obtained by GPS radiosonde flights launched from the same site. This work has utilized these valuable data sets to delineate characteristics of convectively generated gravity waves. A superposition of gravity waves is observed with different scales after the deep convective events. Vertical wave number spectra of radial velocities show steeper slopes and higher power spectral densities during convection which slowly reduce to their normal values. The present case studies suggest the mechanical oscillator mechanism to be a major source of convective gravity wave generation in the tropics. Estimates of vertical wind variances and momentum fluxes of short‐period (<2 h) wind fluctuations show large enhancements on convective days in comparison to control days. The momentum flux frequency spectra revealed a higher contribution of 30–65 min wave periods to the mean profile in the lower stratosphere. The wavelet transform momentum flux spectra displayed the temporal variability and discretization of the gravity wave momentum fluxes in frequency and time.