Analysis of deep convective clouds and their association with non-migrating atmospheric diurnal tides in the tropical troposphere
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Analysis of deep convective clouds and their association with non-migrating atmospheric diurnal tides in the tropical troposphere

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Analysis of deep convective clouds and their association with non-migrating atmospheric diurnal tides in the tropical troposphere

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    The diurnal oscillating tropospheric winds measured by 50 MHz wind profilers located in the tropical Pacific are compared with the tidal winds produced from an f-plane equivalent gravity wave tidal model forced by water vapor solar radiation absorption. The differences between observations and model can not be explained using classical tidal theory with migrating tidal forcing functions. Therefore, the global distribution of latent heat released by diurnal oscillating deep convective clouds is investigated as a possible forcing of the nonmigrating atmospheric diurnal tides in the tropical troposphere. The seasonal distribution of diurnal oscillating deep convective clouds deduced from 3 hour temporal resolution infrared radiance measured by 4 geostationary and 2 polar orbiting satellites were transformed into the zonal wavenumber domain yielding non-migrating structures. The dominant zonal wavenumbers included the westward 5, westward 2, eastward 3, and standing oscillations. The meridional structures were determined by decomposing the dominant wavenumbers with Hough functions. An analytical solution to the vertical structure equation from classical tidal theory was obtained and suggests that some of the observed phase structure is the result of a full-sinewave heating profile with a heating layer above a cooling layer. The cooling is associated with a melting layer. The analytical results show the importance of stratiform rain in forcing the diurnal tidal circulation. The non-migrating modes of latent heating and the migrating water vapor heating rates were used to force an /-plane model and the resulting winds were also compared with the observed diurnal winds measured by 50 MHz wind profilers. The longitudinal interference between non-migrating and migrating tidal modes results in winds with longitudinal dependent amplitudes and nearly migrating phase structures. The inclusion of non-migrating tidal forcing from the global distribution of latent heat released by deep convective clouds can explain some of the differences between the observed diurnal winds across the Pacific as well as discrepancies between observations and current tidal models.
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