||For an equilibrium adiabatic atmosphere and rest basic state, the shallow water model provides a fundamental framework for studying tropical waves. Using such a model on the equatorial beta plane, analytic solution for free equatorial waves can be derived. (Matsuno 1966; Lindzen 1967) Then, Gill (1980) designed a simple model to show solutions for steady tropical motion forced by imposed heating to elucidate basic features of the response of tropical atmosphere to diabatic heating. Several simple atmospheric models were developed later for simulating atmospheric response to SST anomalies after Matsuno and Gill, e.g. Lindzen and Nigam (1987) ; Wang and Li (1992).|
Observation data can be used to explore the forced response by tropical heating, e.g. to evaluate tropical interannual circulation in free atmosphere in response to perturbation condensational heating in Gill model. We used ECWRF Interim data U,V,ϕ as the first baroclinic mode, and used GPCP perturbation precipitation, -ω ̅ (∂s^′)/∂p term, and perturbation radiation term of 1997 December as heating in free atmosphere. We put these heating in the function of Gill model, and estimate the circulation with the observation first baroclinic mode.
Then we find that if we only use perturbation condensational heating on Gill model, the symmetric features Rossby wave spread to the high latitude, and the simulation would be similar to the observation when we combine the -ω ̅ (∂s^′)/∂p term with perturbation condensational heating. -ω ̅ (∂s^′)/∂p is important to let the heating become more symmetrical, and make the symmetric result of circulation become similar to the observation for putting the center of Rossby wave closer to the equator. Its asymmetric result also make the features of circulation more similar to the observation though the value is 0.2 times to the perturbation condensational heating. And the radiation term is an important part of the heating in mean flow, however its influence in eddy is much smaller than others that can be ignored.
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