Atlantic Ocean Tropical/subtropical Processes from the Seasonal to the Decadal Time Scales: Models/Data, Model/Model Comparisons and Model/Data Synthesis through Assim

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This project builds on previous studies and extend them to the more relevant time scales for climate studies, i.e. the interannual to decadal variability of tropical/subtropical interaction in the Atlantic ocean. New research avenues will be pursued: the degree to which decadal-scale changes in the circulation may result from the role of nonlinearities and eddies in determining multiple equilibria states versus more slowly evolving surface forced decadal oscillations. Two hypotheses will be tested. The first one is that The oceanic component of the tropical/subtropical connections in the Atlantic ocean as represented by the STCs significantly affects the interannual to decadal low-latitude SST variability and hence plays a significant role in climate variability. The second one poses that Low-frequency variability in the multi-annual and decadal time scales exist in the tropical.subtropical wind-driven circulation that are associated with nonlinear eddy processes and lead to multiple states characterized by different energetics which produce lo-frequency variability in the meridional heat transport. Most studies of the variability of tropical/subtropical interactions have focused on the deterministic response to surface forcings in the same spectral range. The PI's will explore a venue of low-frequency variability to our knowledge never investigated before in the tropical ocean, i.e. to assess the possible role of internal modes of variability linked to multiple states of the wind-driven circulation produced by eddy-mean flow interactions, modes possibly connected to the analogous modes of decadal variability already found for the subtropical circulation. The approach will use models/data comparisons, model/model comparisons, model/data synthesis through data assimilation, coarse resolution experiments aimed to address hypothesis I and eddy-resolving experiments aimed to address both hypothesis I and II.