Migrating and non-migrating diurnal and semi-diurnal tides over a tropical and an equatorial station

Abstract

VHF radar measurements of hourly winds in the lower atmosphere are utilized to study the diurnal and semi-diurnal tides over two key geographical locations, Gadanki (13.45°E, 79.18°E), India and Kotatabang (0.2°S, 100.2°E), Indonesia. The analysis shows that tidal amplitudes exhibit maxima in upper troposphere lower stratosphere (UTLS) region during June-September over Gadanki and during March and September over Kotatabang. The vertical wavelength is 3-5 km at Gadanki and 25-30 km at Kotatabang in UTLS region, which reveal the existence of non-migrating and migrating tides, respectively. The analysis shows the maximum rainfall during June-September over Gadanki, whereas uniform rainfall throughout the year over Kotatabang. The brightness temperature shows deep (at Gadanki) and shallow (at Kotatabang) convective clouds during these periods. The release of latent heat due to deep convective cloud is found to be the main source mechanism for non-migrating tides at Gadanki. The significance of the present study lies in bringing out the important differences in tidal characteristics over equatorial and low latitude stations.