Abstract
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)
Highlights
Atmospheric solar diurnal tides are global-scale 24 hour oscillations, which are primarily produced by solar thermal excitation of water vapour in the troposphere, and ozone in the stratosphere and mesosphere
We report the observed features of diurnal tidal oscillations in the tropospheric and lower stratospheric horizontal winds measured by MST radar at Gadanki (13.5◦ N, 79.2◦ E) in four seasons, namely, the autumn equinox, winter, vernal equinox and summer seasons
Even if the deviations occur due to the actual atmospheric motions alone, such as gravity waves, for diurnal tidal oscillations they will appear as random errors due to the lack of gravity wave coherence for an interval of nearly two weeks
Summary
Atmospheric solar diurnal tides are global-scale 24 hour (one solar day) oscillations, which are primarily produced by solar thermal excitation of water vapour in the troposphere, and ozone in the stratosphere and mesosphere. We report the observed features of diurnal tidal oscillations in the tropospheric and lower stratospheric horizontal winds measured by MST radar at Gadanki (13.5◦ N, 79.2◦ E) in four seasons, namely, the autumn equinox, winter, vernal equinox and summer seasons. For this purpose, radar wind measurements over 18 diurnal cycles from September 1995 to August 1996 are utilised, with the number of diurnal cycles covered being 3, 7, 3 and 5 in the four seasons, respectively.
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