Indian MST radar observations of gravity wave activities associated with tropical convection

MST radar observations at Gadanki (13.5 degreesN, 79.2 degreesE) of high fr equency (few tens of minutes) gravity waves generated most likely by convec tion are presented. The experiments were conducted during the months of May -June (19 May 1995, 05 June 1995 and 06 June 1996) of summer season, which is likely to be highly convective after the onset of south-west monsoon ove r southern part of India. The excitation and vertical propagation of gravit y waves are found to display specific characteristics pointing convection a s a main source. The intriguing characteristics of rising reflectivity patt ern, coupled with rise in vertical wind component and turbulence from lower troposphere to upper troposphere within hour of time (on 19 May 1995 and 0 6 June 1996) are noticed. On the other day of experiment, horizontal large spread in reflectivity pattern confined mostly below 10 kin of altitude has been observed. During this period wind disturbances are found to posses co mparatively large magnitude of momentum flux at mid-tropospheric levels. Us ually enhanced reflectivity regions are found to be accompanied by strong u pdraft and downdraft in vertical wind component (w). An interesting feature in the case of 05 June 1995 is the appearance of vertical wind disturbance s well up to lower stratosphere. The effect of these enhanced vertical wind is in conformity with the observed increase in the momentum flux values ev en tip to lower stratospheric altitudes. Typical wave amplitude in vertical wind disturbances during convection vary from 1-3 m/s with some sudden enh ancement in amplitude of the order of 8-10 m/s for some short interval of t ime. An effort has been made to discuss these results in the light of exist ing theoretical concepts viz. mechanical oscillator effect, obstacle effect and direct thermal forcing for generating the convection waves (gravity wa ves generated due to convection). (C) 2001 Elsevier Science Ltd. All rights reserved.