Convection over the eastern equatorial Indian Ocean and Iranian branch of Asian summer monsoon anticyclone modulates the wet and dry phases of summer monsoon rainfall over Kerala

This study examined factors affecting wet and dry phases of monsoon rainfall over Kerala, using modern-era retrospective analysis for research and applications (MERRA 2) data set. Based on circulation pattern, our study shows that the wet and dry phases of monsoon over Kerala are related to modulation of convective activity over the eastern equatorial Indian Ocean (EEIO) and the Iranian branch (Western flank) of Asian Summer monsoon anticyclone (ASMA). Outgoing longwave radiation (OLR) and cloud top pressure (CTP) show an anomalous dipole (quadrupole) pattern over the Equatorial Indian Ocean (EIO) during the wet (dry) phase of Kerala summer monsoon rainfall (KSMR). We found that KSMR is enhanced during intensification of the Iranian branch of ASMA and suppressed by anomalous deep convection over the EEIO. Further, anomalous lower level cyclonic circulation over the Western North Pacific (WNP) is pulling low-level jet (LLJ) through Southern Peninsular India, hence playing a vital role in establishing the KSMR wet phase. Contrarily, the dry phase of KSMR is associated with weakening of the Iranian branch of ASMA in the upper level.