Title: Oceanic influence on Large-Scale Atmospheric Convection during co-occurring La Nina and IOD events

Abstract: The ISMR profoundly impacts over a billion people across the region. ISMR extremes have been linked to the ENSO and modulated by the Indian Ocean Dipole (IOD). ISMR of 2022 displayed intriguing spatial patterns: above-normal precipitation over the south peninsula and central India, normal over Northwest India, and below-normal over East and NE India. In 2022, La Nina conditions associated with a negative IOD (nIOD), were prevalent over the equatorial Pacific Ocean (PO) and IO. This study investigates the often-overlooked Oceanic subsurface contribution to large-scale atmospheric convection over the tropical IO. By undertaking a comprehensive analysis, we find that strong equatorial westerly wind anomalies prevailed over the equatorial IO during co-occurring years generating eastward propagating downwelling Kelvin waves which deepens the D20 in the eastern equatorial IO. The Kelvin waves then propagates into BoB and gets reflected from southern tip of India as westward propagating Rossby waves deepening the D20 and causing low level wind convergence in the Northern Arabian Sea(NAS). We identify two centres of low-level wind convergence, one over NAS and another over Maritime Continent during co-occurrence years. These wind convergence centres play a pivotal role in channeling moisture towards their core, also, significantly deepen D20, increase the Ocean heat content and thus maintaining warmer SSTs over area of conversions. Together, these interrelated factors create an environment that is conducive for enhanced convective activity over the zone of convergence, enhancing and sustaining the convective conditions. This study underscores the significant contribution of ocean dynamics in shaping large-scale atmospheric convection during the co-occurrence years, highlighting the significance of considering broader Oceanic variables in comprehending and forecasting monsoonal variability.