DOUBLE ITCZ PHENOMENON AND ANALYSIS OF ITS HEAT BUDGET IN A COUPLED OCEAN-ATMOSPHERE GENERAL CIRCULATION MODEL

The Double ITCZ phenomenon in a coupled ocean-atmosphere general circulation model (CGCM) is studied in this paper and primary analyses of the phenomenon are given from ocean heat budget. Double ITCZ phenomenon is that two ITCZs exist aside of the equator. In coupled circulation models, Double ITCZ is a common phenomenon that is different from that in real climate. Compared the results of numerical experiment with observation, the main characteristics of Double ITCZ are pointed. Different form normal pattern, the most pronounced features of Double ITCZ are to cold SST in warm pool of west Pacific Ocean and to warm SST in a band near 100S of southeast Pacific Ocean.The transition process from a normal ITCZ condition in the initial state to a Double ITCZ mode in the equilibrium state of a coupled ocean-atmosphere general cirulation model is studied in the paper. The results indicate that the transition process happens very fast. And the wind field which also changes fast in tropical Pacific Ocean may play a considerable role in the forming process of Double ITCZ. With each term of ocean heat budgets calculated, the reasons for sea surface temperature changes are gained from analysis of ocean heat budget. Analysis of heat budget in ocean indicates that the SST cooling process in warm pool is mainly affected by diffusion,and the SST warming process in the band near 10°S in the eastern Pacific is affected by anomalous warm advection. This work has pointed out the reason for variety of sea surface temperature in a CGCM,which gave the primary analysis of Double ITCZ phenomenon. However, the further analyses are necessary to gain its explicit physical image.