Abstract
<strong class="journal-contentHeaderColor">Abstract.</strong> 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 80â150-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 (80â150 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 10â20 m s<sup>â1</sup> and 5â10 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.
Highlights
The possibility that latent heat release related to tropical cumulus convective processes may contribute signi®cantly to excitation of the solar semidiurnal atmospheric tide was ®rst proposed by Lindzen (1978) and Hong and Wang (1980), and further studied by Hamilton (1981a)
The heating rates due to these sources are approximately in quadrature, with water-vapor absorption maximizing near noon and the latent heat release occurring in early evening
The current work has focused on the annual mean component so that existing climatological rain gauge data can be included in a self-contained study which compares ground- and satellite-based determinations of rainfall rate
Summary
Latent heat release in the troposphere can be expected to excite various diurnal and semidiurnal vertically propagating oscillations which grow exponentially with height and are dissipated by eddy and molecular diusion between about 80 and 150 km. Hagan et al (1997a) investigated tidal signatures associated with tropospheric latent heat release using the GSWM They employed the heating rates of Williams and Avery (1996) and calculated upper-atmosphere wind perturbations of the order of a few to several m sA1. These investigations focused exclusively on the diurnal tide, but these authors considered the eects of both migrating and nonmigrating components. 7 years of satellite-based threehourly cloud brightness temperature measurements are used to derive the diurnal and semidiurnal components of rainfall rate, and latent heat release, as a function of longitude, between A40° and +40° latitude. The following two sections are devoted to such a speci®cation of global rainfall rate
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