12th Conference on Interactions of the Sea and Atmosphere


Observing and modeling tropical Atlantic atmosphere-ocean interaction

Yochanan Kushnir, Columbia Universtiy, Palisades, NY; and R. Seager and J. C. H. Chiang

The variability of climate in the tropical Atlantic region presents a case where external influences are shaped by a distinctive local atmosphere-ocean interaction, which displays a compelling form of atmospheric reaction to SST variability. Here the large-scale pressure gradient is affected by SST variability, which occurs in response to variations in air-sea heat exchange. The change is pressure affects the near-surface wind circulation, which, in turn, affects the position of the ITCZ and its associated rainfall. The outstanding question is whether this feedback chain leads to multi-year persistent anomalies or quasi-oscillatory behavior with, perhaps, some predictability. The nature of the regional atmosphere-ocean interaction is studied using diagnostic analysis and various models. The talk will describe results from the diagnostic analysis and from a forced ocean GCM experiment. The diagnostic analysis was aimed at understanding the response to external influences and the life cycle of the variability throughout the year. It reveals the strong seasonal “locking” of the ITCZ response. The ocean modeling experiment suggests that the dynamics of the ocean response to surface wind variability is predominantly linear. This hypothesis is tested with the aide of a linear, zonally averaged representation of the basin. The success of this model in simulating the full ocean GCM response provides a tool to test the dynamical coupling between atmosphere and ocean in the region.

Session 1, Tropical Atlantic coupled variability
Monday, 10 February 2003, 9:00 AM-10:15 AM

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