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

摘要

Latent heat release associated with tropicaldeep convective activity is investigated as a source for migrating(sun-synchronous) diurnal and semidiurnal tidal oscillations in the 80–150-kmheight region. Satellite-based cloud brightness temperature measurements madebetween 1988 and 1994 and averaged into 3-h bins are used to determine theannual- and longitude-average local-time distribution of rainfall rate, andhence latent heating, between ±40° latitude. Regional average rainfall ratesare shown to be in good agreement with climatological values derived fromsurface rain gauge data. A global linearized wave model is used to estimate thecorresponding atmospheric perturbations in the mesosphere/lower thermosphere(80–150 km) resulting from upward-propagating tidal components excited by thelatent heating. The annual-average migrating diurnal and semidiurnal componentsachieve velocity and temperature amplitudes of order 10–20 m s–1 and5–10 K, respectively, which represent substantial contributions to the dynamicsof the region. The latent heat forcing also shifts the phase (local solar timeof maximum) of the semidiurnal surface pressure oscillation from 0912 to 0936 h,much closer to the observed value of 0944 h.