Using an atmospheric model of intermediate complexity and a hierarchy of ocean models we investigate the dominant modes of interannual and decadal variability in the South Atlantic Ocean.

The atmospheric model (SPEEDY; Molteni, 2002) has T30L7 resolution. The physical package consists of a set of simplified physical parameterizations schemes, based on the same principles adopted in the schemes of state-of-the-art GCM's. It is at least an order of magnitude faster, whereas the quality of the simulated climate compares well with the GCM's. The hierarchy of ocean models is based in the following strategy. First, we use a simple mixed layer model with an increasing number of physical processes involved such as Ekman transport, barotropic transport and dynamical evaluation of the mixed layer depth. Finally the atmospheric model is coupled to a regional version of the Miami Isopycnic Ocean Model (MICOM) covering the South Atlantic, with a horizontal resolution of 0.5 degree and 15 vertical levels.

The goal of this study is to understand the dominant physical mechanisms responsible for the spatial structure and time evolution of the modes as analyzed from data by Venegas et al.(1997), Sterl and Hazeleger(2002) and Palastanga et al. (2002). Primary results show that horizontal Ekman transport is the principal mechanism for generating the dominant modes of variability in SST. In the ongoing study, we address the question whether these modes are trully coupled or are primarely generated by the atmosphere with a negligible feedback from the ocean.