Articles | Volume 15, issue 9
Special issue:
30 Sep 1997
30 Sep 1997

Upper atmosphere tidal oscillations due to latent heat release in the tropical troposphere

J. M. Forbes, M. E. Hagan, X. Zhang, and K. Hamilton

Abstract. 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-h bins are used to determine the annual- and longitude-average local-time distribution of rainfall rate, and hence latent heating, between ±40° latitude. 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 the latent heating. The annual-average migrating diurnal and semidiurnal components achieve velocity and temperature amplitudes of order 10–20 m s–1 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) of the semidiurnal surface pressure oscillation from 0912 to 0936 h, much closer to the observed value of 0944 h.

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