The dynamics of zonal current variations in the central equatorial Indian Ocean

This paper examines the depth integrated zonal momentum balance in the central equatorial Indian Ocean (0 degrees, 80.5 degrees E) for two periods in 1993-1994 and 2004-2006 using a combination of in-situ and satellite observations. One- to two-year record length mean balances are approximately linear and steady state. Monthly to seasonal time scale variations are also governed by linear dynamics, with imbalances between the pressure gradient force and surface wind stress leading to zonal mass transport variations along the equator. Interannual variations in zonal transports along the equator associated with Indian Ocean Dipole events in 1994 and 2006 are likewise consistent with linear dynamics. These results provide a valuable benchmark for evaluating models of equatorial Indian Ocean circulation on seasonal time scales.