Impact of prolonged La Niٌa events on the Indian Ocean with a special emphasis on southwest Tropical Indian Ocean SST

This study examines the mechanisms governing the teleconnections associated with the long-lived La Niٌa variability in the tropical Indian Ocean (TIO) sea surface temperature (SST) anomalies using observational and reanalysis products. Two long-lived La Niٌa events (1973 to 1976 and 1998 to 2001) are observed in the recent years, one falling before and the other after the mid 1970ʹs climatic shift. The winter (boreal) and spring (November to April) TIO SST is highly influenced by long-lived La Niٌa forcing. Climatic shift in mid 1970s contributes to the changes in TIO SST pattern during these two long-lived La Niٌa events. Surface heat flux variations due to long-lived La Niٌa contribute to the SST changes except in the southwest TIO. The upwelling favorable local surface wind stress curl and upwelling Rossby waves originating from the east are the dominant mechanisms responsible for the La Niٌa related winter time SST cooling over the southwest TIO. Long-lived La Niٌa induced surface wind anomalies enhance the fall Wyrtki Jet in the equatorial Indian Ocean resulting large scale anomalous heat transport. Local SST cooling reduces convection and contributes to the low rainfall over southwest TIO and the northern parts of Madagascar Island.