Interannual Variability of Lower Equatorial Intermediate Current Response to ENSO in the Western Pacific

The ocean currents of the tropical Pacific Ocean vary with El Nino-Southern Oscillation (ENSO) cycles. A mooring time series obtained during 2014-2018 in the western Pacific reveal that interannual variability extends to Lower Equatorial Intermediate Current (LEIC). The LEIC velocity anomalies are significantly correlated with the Nino-3.4 index at an 11-month lag. Monthly velocity data from the global ocean physical reanalysis product and from a linear continuously stratified ocean model during 1993-2018 capture the 2015-2016 signal and are used to identify the underlying mechanism. During El Nino (La Nina) events, the direct wind forcing in the central tropical Pacific and the reflection of Kelvin waves in the eastern Pacific during the first autumn-winter period contribute comparably to an eastward (westward) current anomaly in the western Pacific during the second autumn-winter period. This process is achieved mainly through the generation of the second baroclinic mode and off-equatorial westward-propagating downwelling (upwelling) Rossby waves.