Investigation of convectively generated gravity wave characteristics and generation mechanisms during the passage of thunderstorm and squall line over Gadanki (13.5° N, 79.2° E)

Abstract

This study illustrates the convectively generated gravity wave generation mechanisms during the passage of thunderstorms and squall line using Indian MST radar. For the first time, it has been shown that all three generation mechanisms have been involved in the generation of gravity waves during the passage of squall line event. It is observed that the periodicities in the range of 8–80 min in the tropospheric and 8–32 min in the lower stratospheric regions and vertical wavelengths in the range of 3.2–4.8 km in the tropospheric and 1.2–1.92 km in the lower stratospheric regions are found to be dominant in the present study and are distinctly different during initial, mature and dissipative phases of convection. Amplitude of vertical wind has been weakened (from ~ 4–6 m s−1 to ~ 1 m s−1) considerably after 10–30 min of a convection event. It appears that the wind shear associated with the convective clouds acted like an obstacle to the mean background flow during the squall line passage generated gravity waves. The phase profiles corresponding to the dominant period show both downward and upward propagation of waves. The vertical extent of heating is found to be deeper during squall line event compared with thunderstorm event. From the phase profiles, during 27 September 2004, two peaks of constant phase region are observed. One is due to convective elements and the other is due to strong background wind shear; however, only one peak is observed on 29 September 2004, which is only due to convective processes.