Sea surface temperature and rainfall anomaly over the Bay of Bengal during the El Niño-Southern Oscillation and the extreme Indian Ocean Dipole events between 2002 and 2016

Phenomena like the El Niño-Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) regulate the climate of several nations situated around the Indian Ocean rim as well as the entire globe. The present study focused on the Bay of Bengal (BoB) in the northern Indian Ocean, which is known for its crucial role in the Indian summer monsoon. The sea surface temperature (SST) and rainfall (RF) anomalies in the central, eastern, western and northern BoB were thoroughly analyzed with respect to all the El Niño, La Niña and extreme IOD events between the years 2002 and 2016. Most of the El Niño (La Niña) phases were accompanied by a positive (negative) SST anomaly and a negative (positive) RF anomaly. However, the magnitude of the SST and the RF anomalies did not co-vary with Oceanic Niño index observed in the Niño 3.4 region. The SST and RF anomalies in the BoB lagged the onset of El Niño by 1-7 months and 3 months, respectively. During La Niña, a negative SST anomaly was accompanied by a positive RF anomaly; however, the magnitude of the anomaly in case of both parameters was larger during El Niño phases when compared to the La Niña phases. Longer El Niño periods corresponded to larger reductions in rainfall in BoB. In general, El Niño is accompanied by positive IOD phase and La Niña by negative IOD phase. We observed a negative rainfall anomaly in the BoB during a positive IOD and vice versa. However, this trend reversed whenever El Niño coincided with negative IOD and La Niña with positive IOD. This showed that whenever an El Niño or La Niña coincided with the conventionally opposite IODMI phases, the effect of ENSO phases overruled the IODMI phases in BoB. Many previous studies have documented that SST and RF anomalies can potentially regulate as well as helps to forecast both droughts and floods in landmasses, not only in the vicinity to oceans but also inner continental regions. Since BoB plays a crucial role in regulating the monsoon and India being a monsoon dependent agricultural nation, the present observations may be of help to climate modelers to study the effect of SST anomalies in BoB (with respect to synoptic scale events like ENSO or IOD) upon the regional climate of India.