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Ann. Geophys., 15, 1165-1175, 1997
www.ann-geophys.net/15/1165/1997/
© European Geosciences Union 1997
Upper atmosphere tidal oscillations due to latent heat release in the tropical troposphere
J. M. Forbes1, M. E. Hagan2, X. Zhang1, and K. Hamilton3
1Department of Aerospace Engineering Sciences, University of Colorado, Boulder, CO, 80309
2High-Altitude Observatory, National Center for Atmospheric Research, Boulder, CO, 80307-3000
3Geophysical Fluid Dynamics Laboratory/NOAA, Princeton University, Princeton, New Jersey
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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