HR: 1300h
AN: OS52D-01    [PDF]
TI: The Role of the Annual Cycle in Tropical Atlantic Variability
AU: * Bates, S C
EM: sbates@cola.iges.org
AF: George Mason University, School of Computational Sciences 4400 University Drive, Fairfax, VA 22030-4444 United States
AB: The anomalous variability of sea surface temperature (SST) in the tropical Atlantic Ocean has been shown to be dependent on its annual cycle. The two primary modes of interannual variability in the tropical Atlantic are a meridional and an equatorial mode; both of which involve North-South displacements of the ITCZ, as found in the annual cycle, and are linked to the position of the ITCZ on year-to-year and decadal time scales. Other research asserts that anomalous atmospheric circulation patterns over the northern tropical Atlantic are phase-locked to the seasonal cycle. A sequence is suggested in which the March-April-May SST pattern forces a wind anomaly, which acts to shift the ITCZ. In addition, composites of wind stress and SST are only distinct from climatology for a couple of months out of the year. A comprehensive data analysis that includes a long observational record and various model data is performed in order to identify how well each model represents tropical Atlantic variability. Relationships between SST, wind stress, and heat fluxes are examined, including those mentioned above. In addition to the data analysis, a series of state-of-the art coupled GCM experiments are presented in order to examine how the annual cycle affects the SST variability. The model used is the Poseidon Ocean General Circulation Model (GCM) coupled with the COLA atmospheric GCM. The coupled model has well known errors in its excessively warm SST south of the equator associated with large meridional migration of the ITCZ with seasons. In the first experiment, these phase errors are corrected through anomaly coupling to examine the potential improvement of anomalous SST simulation due to the corrected seasonal cycle in the model. Subsequent experiments involve holding the model perpetually in one season. These experiments are designed to give insight into which season is most important for the generation of the leading patterns of SST variability and how the evolution of the annual cycle affects them. Conclusions are drawn as to which physical mechanisms of the annual cycle are most important in the generation of SST variability in the tropical Atlantic Ocean.
DE: 4215 Climate and interannual variability (3309)
DE: 4227 Diurnal, seasonal, and annual cycles
DE: 4231 Equatorial oceanography
DE: 4504 Air/sea interactions (0312)
SC: Ocean Sciences [OS]
MN: 2004 Ocean Sciences Meeting