Upper Atmosphere Tidal Oscillation Due to Latent Heat Release in the Tropical Troposphere

Latent heat release associated with tropical deep convective activity is investigated as a source for migrating (sun-synchronous) diurnal and semidiurnal tidal oscillations in the 80-150 km height region. Satellite-based cloud brightness temperature measurements made between 1988 and 1994 and averaged into 3-hourly bins are used to determine the annual and longitude-average rainfall rate, and hence latent heating, between 40 S and 40 N. Regional average rainfall rates are shown to be in good agreement with climatological values derived from surface rain gauge data. A global linearized wave model is used to estimate the corresponding atmospheric perturbations in the mesosphere/lower thermosphere (80-150 km) resulting from upward-propagating tidal components excited by latent heating. The annual-average migrating diurnal and semidiurnal components achieve velocity and temperature amplitudes of the order of 10-20 m/s and 5-10 K, respectively, which represent substantial contributions to the dynamics of the region. The latent heat forcing also shifts the phase (local solar time of maximum) from 0912 to 0936 hr, much closer to the observed value of 0944 hr.