Seasonal variation of short‐period (<2 h) gravity wave activity over Gadanki, India (13.5°N, 79.2°E)

Abstract

We have analyzed the seasonal variation of short‐period (<2 h) gravity wave activity in the troposphere and lower stratosphere using the wind observations made with VHF radar at Gadanki (13.5°N, 79.2°E), India. Four years of high resolution (∼3 min) wind data (2003–2006) have been used to study variance and momentum flux of short‐period gravity waves. Both horizontal and vertical variances show annual variation. Variances in the upper troposphere (12–16 km) and lower stratosphere (18–21 km) are found to maximize in the wet months of June–July–August coinciding with the peaks of outgoing longwave radiation (OLR) and the rain rate (surface and Tropical Rainfall Measuring Mission [TRMM] 2 km rainfall). An additional strong peak of variance is observed in the height ranges of 4–12 km during spring which corresponds to TRMM storm height maximum. The measurements suggest deep convective activity to be the main source of short period gravity waves. Variances in the UTLS region are found to correlate well with square of wind shear indicating possible in situ generation of the gravity waves. Topographic generation of short period gravity waves does not seem to be important for this site. An interannual variability is observed in the measured wave activity. Zonal momentum flux shows annual variation with westward preference in the wet season whereas the meridional flux does not indicate any clear variation.