ENSO and the recent warming of the Indian Ocean

Abstract

ABSTRACT:The recent Indian Ocean (IO) warming and its relation with the El Niño Southern Oscillation (ENSO) is investigated using available ocean and atmospheric reanalyses. By comparing the events before and after 1976 (identified as a threshold separating earlier and recent decades with respect to global warming trends), our results indicate that the IO had experienced a distinct change in the warming pattern. After 1976, during the boreal summer season the cold anomalies in the IO were replaced by warm anomalies in both warm (El Niño) and cold (La Niña) ENSO events. Strong sinking by upper level winds and the associated anomalous equatorial easterly winds created favourable conditions for the IO warming from 90 ∘ E towards the western IO. Our study highlights that after 1976, atmospheric and oceanic fields changed mostly during La Niña, with both ENSO phases contributing to the warming of the IO. Warm anomalies of 0.2 ∘ C are seen over large areas of the IO in the post-1976 La Niña composites. Our analysis suggests that the IO warming during La Niña events after 1976 may have a relation to the warm anomalies persisting from the preceding strong El Niño events.

Large-Scale Mode Impacts on the Sea Level over the Red Sea and Gulf of Aden

“…Weak (strong) wind typically occurs during El Niño (La Niña) [64,65]. However, after the early 1980s, there was a weakening and shift that were included behind the surface wind to the SST [58,66], which means that this shift took place over 30 years ago and still continues, which is consistent with our results. Nakamura et al (2009) [67] suggested that a warming of the Western IO has driven the observed shift by acting as a barrier for ENSO influencing the IO circulation, including the GA and RS.…”

“…This situation forces the normal surface wind in the IO either to be weak westerly or to completely change direction to easterly. Previous studies reported vividly that the dominant mode of surface wind and SST in the IO is closely related to ENSO [49,51,[56][57][58].…”

Indian Ocean warming as a driver of the North Atlantic warming hole

“…Then what could have caused the strengthening of surface westerlies? We now turn attention to the tropical Indian Ocean (TIO) whose temperature has increased by about 1°C since the mid-1950s [17][18][19][20][21][22][23][24][25][26][27] , at a faster rate than that of the other two tropical oceans ( Fig. 1a).…”

Genesis and Trends in Marine Heatwaves Over the Tropical Indian Ocean and Their Interaction With the Indian Summer Monsoon

“…It is observed that the longterm persistence of MHWs in the western Indian Ocean region is associated with the background SST warming primarily identified with the Indian Ocean basin-wide warming (IOB) and also the El Niño, IOD, and NAO Roxy et al (2014). andAbish et al (2018) show that the western Indian Ocean is warming at a rapid pace since the 1950s, largely in response to anthropogenic warming but manifested through an asymmetry in the ENSO impact-whereby El Niño events cause anomalous warming in the western Indian Ocean and La Niña events fail to cool the region. They also found that the ENSO events are more intense in the recent decades and this result in a positive SST skewness Han et al (2010).…”