Influence of ENSO Events on the Agulhas Leakage Region

This study explores the subsurface oceanic response to the El Niño Southern Oscillation (ENSO) in the southern tropical Indian Ocean and Agulhas leakage region. The subsurface temperature and salinity responses of the southern tropical Indian Ocean and Agulhas leakage are studied using Argo float data. In addition, AVISO satellite-derived sea surface height (SSH) data is used to examine the propagation of an ENSO signal across the Indian Ocean to the Agulhas leakage region and its impact on eddy propagation within the leakage region. During the peak of an ENSO event, the Indian Ocean basin is anomalously warm up to 500 m depth in response to El Niño, but anomalously cool in response to La Niña. Sea surface salinity is anomalously fresh for both events in the eastern and western Indian Ocean basins, but the subsurface salinity signal during El Niño is anomalously saline to about 150 m in both basins. The subsurface signals last approximately 1 year (2 years) after the peak of ENSO in the eastern (western) Indian Ocean basin. The subsurface signal in the Agulhas leakage region is anomalously warm 2 years after El Niño and anomalously cool 2 years after La Niña. Westward propagation of SSH anomalies across the Indian Ocean basin is evident at 12°S and 25°S latitudes and it takes 2 years for the initial signal of Rossby waves to reach Agulhas leakage region after the peak of an ENSO event.