Dynamics of the Indian Ocean response to atmospheric intraseasonal oscillations

The Regional Oceanic Modeling System (ROMS) is used to explore the relationship between intraseasonal (20-90 days) atmospheric zonal flow and the surface dynamics of the equatorial Indian Ocean. To gain an understanding of the interaction between these two processes, the model is run considering two experiments for the tropical Indian Ocean, north of 29ºS. In the first experiment, wind climatology forces the model, while in the second experiment the wind forcing includes the observed intraseasonal variability. Special attention is placed on the year 1999, where model integrations can be directly compared with data collected during the Joint Air-Sea Monsoon Interaction Experiment (JASMINE). Model runs with wind forcing in the intraseasonal band display 40-60 day zonal surface currents in the equatorial Indian Ocean, congruent with observations. In particular, for the JASMINE period the zonal surface currents display a 50-day oscillation. The intraseasonal winds influence ocean currents causing variability in sea surface temperatures which in turn feedback to the atmosphere implying ocean-atmosphere coupling. Additionally, the sea level data displays a 90-day spectral peak in the TOPEX/Poseidon data, implying a direct relationship with processes that occur in the intraseasonal band.