Recent changes in the prominent modes of Indian Ocean dipole in response to the tropical Pacific Ocean SST patterns

Abstract

The present study examines the prominent patterns of Indian Ocean dipole (IOD) associated with the recent changes in the Pacific Ocean variability centered around 1998. EOF analysis of boreal fall (September through November (SON)) Indian Ocean sea surface temperature anomaly (SSTA) reveals that EOF1 (32% variability) is dominated by East Pacific El Nino-IOD co-occurring pattern during 1980–1998 (period 1). During period 2 (1999–2016), central Pacific El Nino also influence EOF1 (26% variability) and the IOD co-occurrence is reduced. EOF2 with 22% variability has central Indian Ocean dipole pattern co-occurred with El Nino Modoki during period 1, and it became basin-wide south-north dipole pattern in period 2 with reduced (20%) variability. At the same time, local Indian Ocean variability induced by SST anomalies centered on western side of Australia (Ningaloo Nino/Nina) is found to be related to EOF2 in both the periods and its influence is stronger after 1998, when its association with El Nino weakens. Third mode is ENSO independent IOD pattern in both the epochs and has more variability in period 2. Thus, during period 1, both East Pacific and central Pacific El Nino events are well separated as major two modes of tropical Pacific Ocean. These two flavors are associated with two different IOD patterns. But in the second period, first mode of Pacific Ocean is strongly related to both the El Nino flavors and reduced the co-occurrence of IOD with the El Nino modes and the effect of local Indian Ocean processes in the IO variability is intensified.