Study of the Dynamics and Maintenance of the Intertropical Convergence Zones

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The Intertropical Convergence Zones (ITCZs) are climatological features in the earth's atmosphere that are intimately tied to both the tropical large-scale meridional (Hadley) circulation and the low-latitude surface circulation. The ITCZ drives the meridional circulation cells which transport momentum and excess heat from the tropics to midlatitudes, thereby affecting the baroclinity of the midlatitudes and hence climate. In addition, the eastern Pacific ITCZ appears to play a role in the large El Nino/Southern Oscillation climate fluctuations. Yet the dynamics and energetics of the processes maintaining the Intertropical Convergence Zones are poorly understood. This study examines the maintenance of the ITCZ phenomenon and the associated large-scale circulation, using a General Circulation Model and a simplified 3-layer model of the tropical atmosphere. The PI is completing a series of carefully designed GCM experiments with increasingly complicated forcing that explores how the surface boundary heating (sea surface temperature) and orography affect the location, strength, energetics and dynamics of the ITCZ. A 3-layer model of the tropical atmosphere has been constructed and employed to facilitate the interpretation of the GCM experiments (this model explicitly resolves the boundary layer and the free baroclinic tropical tropospheric circulations). These results are helping to better define the relationship between the ITCZ and large-scale meridional and surface circulations, and hence are contributing to our knowledge of the global climate.