National Oceanic and
Atmospheric Administration
United States Department of Commerce


FY 2015

Volume transport of the Wyrtki jets and their relationship to the Indian Ocean dipole

McPhaden, M.J., Y. Wang, and M. Ravichandran

J. Geophys. Res., 120(8), 5302–5317, doi: 10.1002/2015JC010901 (2015)

The equatorial Indian Ocean is characterized by strong eastward flows in the upper 80–100 m during boreal spring and fall referred to as the Wyrtki jets. These jets are driven by westerly winds during the transition seasons between the southwest and northeast monsoons and represent a major conduit for mass and heat transfer between the eastern and western sides of the basin. Since their discovery over 40 years ago, there have been very few estimates from direct observations of the volume transports associated with these currents. In this paper we describe seasonal-to-interannual time scale variations in volume transports based on 5 years of unique measurements from an array of acoustic Doppler current profilers in the central equatorial Indian Ocean. The array was centered at 0°, 80.5°E and spanned latitudes between 2.5°N and 4°S from August 2008 to December 2013. Analysis of these data indicates that the spring jet peaks in May at 14.9±2.9 Sv and the fall jet peaks in November at 19.7±2.4 Sv, around which there are year-to-year transport variations of 5–10 Sv. The relationship of the interannual transport variations to zonal wind stress forcing, sea surface temperature, sea surface height, and surface current variations associated with the Indian Ocean Dipole (IOD) are further highlighted. We also illustrate the role of wind-forced equatorial waves in affecting transport variations of the fall Wyrtki jet during the peak season of the IOD.

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