Mechanisms for the Northward Displacement of the Pacific Intertropical Convergence Zone (ITCZ)

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The project will investigate the causes for the off-equatorial location of the Inter-Tropical Convergence Zone (ITCZ). The confluence of northeast and southeast trade winds generates the moisture flux convergence that feeds deep tropical convection. The convection shows up as a bright cloud band in satellite pictures, and helps identify the ITCZ. Although solar forcing is nearly symmetric in the annual-mean, the ITCZ in the central/eastern Pacific remains northward of the equator throughout much of the year. Recent studies have revealed the role of ocean-atmosphere interactions in equatorial and coastal zones, and of geographical asymmetries of continents (e.g., the Americas) in producing the Northern hemisphere location of the ITCZ, but many key questions remain unanswered. Not surprisingly, the ITCZ remains a poorly simulated feature in current climate models. Drs. Shang-Ping Xie and Tim Li will identify the key climate interactions that control ITCZ location from modeling analysis, using a pair of coupled climate models. The PIs will decompose the geographical asymmetries of the Americas into several elements and investigate their "symmetry-breaking" potential in context of ITCZ's meridional position. They will also investigate the interaction of the eastern Pacific ITCZ and the North American monsoon. This research will advance the understanding of how ocean, land, and the atmosphere interact to shape the eastern Pacific climate. In so doing, it will provide the large-scale interpretive framework for NSF's Eastern Pacific Investigation of Climate (EPIC) field program, and also contribute to the Pan American/Pacific research goals of the U.S. CLIVAR program.