Indian summer monsoon variability over North-East India: Impact of ENSO and IOD

Abstract

The influence of phase and amplitude of Indian Ocean Dipole (IOD) and El Niño Southern Oscillation (ENSO) on the interannual variability of the Indian summer monsoon rainfall (ISMR) over North East India (NEI) has been studied first time from 1960 to 2015. The independent contribution of different phases and amplitude of IOD and ENSO in the interannual variabilities of ISMR over NEI is explained by correlation and found that precipitation decreases due to anomalous wind vector from the Bay of Bengal (BOB) to the Sumatra region. The northeasterly wind also reduces the advecting moisture towards NEI during pure positive IOD event years (PPIOD) at 850 hPa. Conversely, a positive anomaly was found in the BOB during the Pure El Niño event years (PEN) due to the SST anomaly in the east-central Pacific Ocean before the beginning month of the summer monsoon. Similarly, pure negative IOD event years (PNIOD) also show positive anomaly, which results in the moderate southwest monsoon. Because of the random composite circulation field, the changes in mean monsoonal rainfall are not much significant during the pure La Niña event years (PLN). These studies show the direct influence of the ENSO and IOD phenomenon on ISMR over NEI.