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

Priyanka Ghosh*(1) and T. K. Ramkumar(1), V. Yesubabu(1), C. V. Naidu(2)
(1) National Atmospheric Research Laboratory, Gadanki 517112, Chittoor, AP, India
(2) Dept. of Meteorology and Physical Oceanography, Andhra University, 530003, India

Using a mesosphere stratosphere troposphere radar operating at 53 MHz, the present work reports that during a convection event occurred over the Indian tropical station of Gadanki at 22.14 hrs – 23 hrs. IST on 06 June 2011, all these three source mechanisms played important roles in determining the characteristics of internal atmospheric gravity waves generated: (1) latent heating of convection, (2) mechanical oscillation of up and down drafts and (3) obstacle effect of wind flows over convective towers near the tropopause level. It is found that while the depth of heating determines the vertical wavelength of gravity waves, the oscillation frequency of up and down drafts determine the observed frequency of waves. From the study of vertical structure of phase and vertical wind velocities, it is observed that while the ~13 min. and ~26 min. oscillations are associated with mechanical oscillator mechanisms, the ~17 min. oscillation is associated with obstacle effect. Combined Fourier and Morlet wavelet transform analyses of all the three components of wind velocities, measured by the MST radar, showed the clear association of gravity waves generated from convection and the vertical propagation characteristics of the gravity waves are found to be in good agreement with theoretical expectations. With the back ground atmospheric information obtained from the GPS radiosonde and ERA-Interim reanalyses data, the high resolution Weather Research Forecast (WRF) model simulation supports the present observations that in turn help in a large way to the progress of parameterization of convection-generated high-frequency gravity waves in general circulation models. The present work also finds that water molecules induced distinct polarized refractive index structures are in existence, which is in accordance with an earlier report on this subject.


*email: priyanka@narl.gov.in
*Preference: Poster