Convection‐generated high‐frequency gravity waves as observed by MST radar and simulated by WRF model over the Indian tropical station of Gadanki

Abstract

Using a Mesosphere–Stratosphere–Troposphere (MST) radar operating at 53 MHz, the present work reports that during the development of convection over the Indian tropical station of Gadanki at 1638–1730 UTC on 6 June 2011, all the following three source mechanisms played important roles in determining the characteristics of high‐frequency internal‐atmospheric gravity waves generated: (i) latent heating of convection, (ii) mechanical oscillation of up‐ and down‐draughts associated with convection, and (iii) obstacle effect of wind flows over convective towers near the tropopause level. In general, it is found that while the depth of latent heating determines the vertical wavelength of gravity waves, the oscillation frequency of up‐ and down‐draughts determines the observed frequency of waves. From the study of vertical structure of vertical wind velocities and phases of three waves (∼13, ∼17 and ∼26 min) generated during this event, it is observed that while the ∼13 and ∼26 min oscillations are associated with the mechanical oscillator mechanism, the ∼17 min oscillation is associated with the obstacle effect. Analyses (Fourier, Morlet‐wavelet transforms and maximum entropy method (MEM)) of all three components of wind velocity, measured by the MST radar, show that there is a clear association of gravity waves generated with convection, and the vertical propagation characteristics of the gravity waves are found to be in good agreement with theoretical expectations. With the background atmospheric information obtained by using the data of GPS radiosondes, ERA‐Interim and NCEP‐NCAR reanalyses, high‐resolution Weather Research and Forecasting (WRF) model simulations support the present observations that in turn will help in a large way to the progress of parametrization of convection‐generated high‐frequency gravity waves in general circulation models. The present work also finds that water molecules induced distinct atmospheric polarized‐refractive‐index structures into existence, which is in accordance with an earlier report on this subject.