Intraseasonal variability in the upper layer currents observed in the eastern equatorial Indian Ocean

Abstract

Direct observations of the upper ocean velocity in the eastern equatorial Indian Ocean by an acoustic Doppler current profiler, from November 2000 to October 2001 on the equator at 90°E, demonstrate that the dominant periods of variability in the upper layer zonal and meridional currents are in intraseasonal frequency bands with periods of 30 to 50 days and 10 to 20 days, respectively. The strong intraseasonal variability in the zonal current obscures the semiannual Wyrtki jets, which can be seen clearly in the monthly averaged field. In addition, a zone of strong vertical shear of the zonal current and a distinct Equatorial Undercurrent with semiannual period are observed. The results provide us with a new perspective on importance of the energetic intraseasonal variability in the eastern equatorial Indian Ocean, which indicates strong correlation with the wind variability near the mooring location.