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Ann. Geophys., 19, 991-999, 2001
www.ann-geophys.net/19/991/2001/
© European Geosciences Union 2001
Tidal wind oscillations in the tropical lower atmosphere as observed by Indian MST Radar
M. N. Sasi, G. Ramkumar, and V. Deepa
Space Physics Laboratory Vikram Sarabhai Space Centre, Trivandrum 695 022, India
Abstract. Diurnal tidal components
in horizontal winds measured by MST radar in the troposphere and lower
stratosphere over a tropical station Gadanki (13.5° N, 79.2° E) are presented
for the autumn equinox, winter, vernal equinox and summer seasons. For this
purpose radar data obtained over many diurnal cycles from September 1995 to
August 1996 are used. The results obtained show that although the seasonal
variation of the diurnal tidal amplitudes in zonal and meridional winds is not
strong, vertical phase propagation characteristics show significant seasonal
variation. An attempt is made to simulate the diurnal tidal amplitudes and
phases in the lower atmosphere over Gadanki using classical tidal theory by
incorporating diurnal heat sources, namely, solar radiation absorption by water
vapour, planetary boundary layer (PBL) heat flux, latent heat release in deep
convective clouds and short wave solar radiation absorption by clouds. A
comparison of the simulated amplitudes and phases with the observed ones shows
that agreement between the two is quite good for the equinox seasons,
especially the vertical structure of the phases of the meridional wind
components.
Key words. Meteorology and
atmospheric dynamics (tropical meteorology; waves and tides)
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