A Wake due to the Maldives in the Eastward Wyrtki Jet

Abstract

wake due to islands in background zonal flow has been observed in the equatorial Pacific Ocean. This study detects and examines a wake due to the Maldives in the eastward Wyrtki jet in the Indian Ocean. Observations by acoustic Doppler current profilers deployed east of the Maldives show semiannual variability in cross-equatorial currents, which cannot be explained by annual monsoonal wind forcing. Output from a high-resolution ocean general circulation model (OGCM) shows that the semiannual current variability is a part of a stationary wavelike pattern of meridional currents, which appears east of the Maldives concurrently with the eastward Wyrtki jet. Idealized numerical experiments are conducted using a 1.5-layer model, in which an equatorial jet driven by wind forcing or steady inflow impinges islands that are similar to the Maldives in shape. The results show the meandering of the equatorial eastward jet east of the model islands, and the resulting cross-equatorial currents have a similar pattern compared to those in the OGCM simulation. The momentum budget analysis obtained from the OGCM simulation and the layer model experiments shows a significant contribution of momentum advection to the generation of the wake. Also, the layer model experiments exhibit that the wake is essentially stationary; its zonal wavelength becomes larger when the eastward jet is stronger, and the wake is absent when the equatorial jet is westward. The similarity of the wake in the equatorial jet to stationary damped Rossby waves in the quasigeostrophic barotropic ocean model is discussed.