1.5 Observed tropical diabatic heating profiles and their projections on the vertical modes

Monday, 8 June 2009: 9:20 AM
Pinnacle BC (Stoweflake Resort and Confernce Center)
Chidong Zhang, Univ. of Miami/RSMAS, Miami, FL; and S. M. Hagos

The applicability of Gill-type models with a single vertical mode is based on an assumption that there is one dominant vertical profile of diabatic heating in the tropics. This might be a reasonable assumption for an atmosphere of a steady state or low-frequency (seasonal and interannual) variability when the mean diabatic heating profile resembles a sinusoidal function with its amplitude peaking in the mid troposphere and vanishing at the surface and tropopause. When transient motions (i.e., tropical waves) are considered this assumption is no longer valid. Diabatice heating profiles based on in situ sounding observations exhibit three prevailing large-scale vertical structures: shallow and bottom heavy (peak near 700 hPa), deep and middle heavy (peak near 500 hPa), and stratiform and top heavy (heating peak near 400 hPa and cooling peak near 700 hPa). These prevailing large-scale heating structures arise from differences in composition of meso-scale convective systems. It is shown that each of them projects on a set of vertical dynamical modes. In combination, several vertical modes with the largest amplitudes emerge as the dominant ones. The results from this study provide an observational basis to determine which of the dominant vertical modes should be included in a theoretical framework that is simple enough for mathematical analysis and complete enough to represent essential physical processes for the problem under study. A framework for problems related to air-sea interaction where surface wind is essential, for example, should consist of different vertical modes from that for problems related to upper-tropospheric wave trains.
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