Study of the Dynamics of the Intertropical Convergence Zone with a Symmetric Version of the GLAS Climate Model

Abstract

The results of some calculations with a zonally symmetric version of the Goddard Laboratory of Atmospheric Sciences (GLAS) climate model are described. The model was first used to study the nature of symmetric circulation in response to various zonally-averaged latent heating fields based on observations. Three experiments with distribution of Intent beating corresponding to the equinox condition, Northern Hemisphere summer condition and south Asian monsoon condition showed reasonable similarity to the observed distribution of surface easterlies and westerlies and the subtropical westerly jets. In the south Asian monsoon experiment, surface westerlies as well as the upper-level easterly jet in the subtropics of the Northern Hemisphere were found. The strength of the subtropical westerly jet increased with decrease in the vertical eddy viscosity. Additional experiments were carried out in which the model was allowed to determine its own latent beat sources and the results were analyzed to examine the interaction of CISK and the imposed SST in determining the position, structure and transient behavior of the ITCZ. In the small number of cases considered, the model equilibrium was found to be independent of initial conditions, with a narrow ITCZ occurring over the SST maximum. After the equilibrium solution was established, the specfied SST distribution was altered. It was found that the initial ITCZ persisted for a long time (weeks to months); however, finally a new ITCZ became established at the location of the new SST maximum. Initially its development was slow, but was followed by a rapid intensification toward the end. The time needed for the establishment of the ITCZ at its new position depended upon the latitude of maximum SST and the magnitude of the SST anomaly. The calculations also indicated the properties of some of the parameterizations employed in the climate model, in particular, the moist convection and the effects of clouds on radiative cooling.