Dynamics on Seasonal Variability of EKE Associated with TIWs in the Eastern Equatorial Pacific Ocean

Abstract

AbstractEnergetic mesoscale eddies (vortices) associated with tropical instability waves (TIWs) exist in the eastern equatorial Pacific Ocean between 0° and 8°N. This study examines the seasonal variations in eddy kinetic energy (EKE) of TIWs using in situ and satellite observations and elucidates the underlying dynamical mechanisms. The results reveal that the cross-equatorial southerly winds are key to sustaining the high-level EKE (up to ~600 cm2 s−2) from boreal summer to winter in 0°–6°N and 155°–110°W. Because of the β effect and the surface wind divergence, the southerly winds generate anticyclonic wind curls north of the equator that intensify the sea surface temperature (SST) fronts and force the downwelling annual Rossby waves. The resultant sea surface height ridge induces strong horizontal current shears between 0° and 5°N. The intensified current shears and SST fronts generate EKE via barotropic and baroclinic instabilities, respectively. To the extent that the seasonal migration of a northward-displaced intertropical convergence zone intensifies the southerly winds north of, but not south of, the equator, our study suggests that the climatic asymmetry is important for the oceanic eddy generations in the eastern equatorial Pacific Ocean—a result with important implications for coupled climate simulation/prediction.