Seasonal variation of the zonally symmetric tropical circulation in a simple climate ,model

Abstract

A low-order model of the zonally symmetric tropical circulation is developed. The model equations are linearized about a resting basic state and are solved on an equatorial beta-plane. The circulation is forced by the solar radiation. The vertical structure is separated by specifying a first baroclinic mode. The time-dependence of the variables is specified by a truncated Fourier series. This results in a system of coupled ordinary differential equations with latitude as the independent variable. The moisture equation is decoupled from the system by assuming saturation in the regions of ascent. A finite-difference technique is used to solve the two-point boundary-value problem. Surface temperature perturbations and latent heating are determined interactively with the circulation. The surface (ocean/land) processes are modeled by incorporating certain time constants which are functions of appropriate surface and atmospheric parameters.

The results of the numerical experiments with all-ocean, all-land, and ocean-cum-land surfaces show:

i) the effect of direct absorption of solar radiation by the atmosphere, ii) the effect of the different time constants for the ocean, land, and atmosphere, and iii) the effect of the oceanic and continental surface contrast in the ocean–cum–land case, resulting in secondary maxima of surface temperature and vertical velocity.