National Oceanic and
Atmospheric Administration
United States Department of Commerce


FY 2011

Dynamics of zonal current variations associated with the Indian Ocean dipole

Nagura, M., and M.J. McPhaden

J. Geophys. Res., 115, C11026, 12 pp, doi: 10.1029/2010JC006423 (2010)

This study examines interannual variability in the equatorial Indian Ocean using observations and a continuously stratified linear long-wave ocean model driven by European Centre for Medium-Range Weather Forecasts winds. Our focus is on the relationship between wind stress, zonal velocity, and sea surface height (SSH) in association with the Indian Ocean dipole (IOD). The model correctly simulates the dominant pattern of variability associated with the IOD in which SSH anomalies near the equator tend to tilt zonally in phase with zonal wind forcing. Both observations and the model also show that surface zonal velocity on the equator tends to lead zonal wind stress by about 1 month on interannual time scales. This phasing occurs because velocity anomalies reverse before the wind anomalies reverse during the decay of IOD events. The model simulations indicate that this reversal of velocity earlier than winds is caused by reflected Rossby waves radiating from the eastern boundary. These results have important implications for understanding the evolution of IOD events because of the role of zonal advection in determining interannual variations in equatorial Indian Ocean sea surface temperature anomalies.

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