Investigating the Dominant Source for the Generation of Gravity Waves during Indian Summer Monsoon Using Ground-based Measurements

Over the tropics, convection, wind shear (i.e., vertical and horizontal shear of wind and/or geostrophic adjustment comprising spontaneous imbalance in jet streams) and topography are the major sources for the generation of gravity waves. During the summer monsoon season (June–August) over the Indian subcontinent, convection and wind shear coexist. To determine the dominant source of gravity waves during monsoon season, an experiment was conducted using mesosphere-stratosphere-troposphere (MST) radar situated at Gadanki (13.5°N, 79.2°E), a tropical observatory in the southern part of the Indian subcontinent. MST radar was operated continuously for 72 h to capture high-frequency gravity waves. During this time, a radiosonde was released every 6 h in addition to the regular launch (once daily to study low-frequency gravity waves) throughout the season. These two data sets were utilized effectively to characterize the jet stream and the associated gravity waves. Data available from collocated instruments along with satellite-based brightness temperature (TBB) data were utilized to characterize the convection in and around Gadanki. Despite the presence of two major sources of gravity wave generation (i.e., convection and wind shear) during the monsoon season, wind shear (both vertical shear and geostrophic adjustment) contributed the most to the generation of gravity waves on various scales.