The the Indian summer monsoon onset in Kerala (MoK) has large socioeconomic implications for the densely populated Indian subcontinent, yet understanding the associated air–sea interactions remains challenging for the scientific community. In this study, we first show that the preceding El Niño–Southern Oscillation (ENSO) accounts for approximately two-thirds of the interannual variability of the Arabian Sea mini warm pool (MWP), whereas the preceding Indian Ocean dipole (IOD) has minimal influence. Following an El Niño event, a strong anticyclone develops over the northern Arabian Sea from April to June due to the anomalous easterlies that weaken the mean southwesterly winds over the southeastern and central Arabian Sea. It, thus, simultaneously favors the MWP expansion in May and delays the MoK, establishing a positive correlation between the two (a strong MWP being statistically associated with a delayed onset). In contrast, after a La Niña event, the southwesterly monsoon winds remain strong, resulting in a weak or absent MWP. To examine the direct influence of the MWP on the MoK, we have employed a regional coupled atmosphere–ocean numerical model (RCM). The "noMWP" sensitivity experiments suggest that following an El Niño year, as the MWP intensifies, it draws winds toward the Kerala coast, enhancing convective activity and causing an early MoK. Consequently, the MWP helps advance the MoK, mitigating the delay that would otherwise be more pronounced after an El Niño. These findings underscore the importance of improving the observation and simulation of MWP dynamics to enhance monsoon forecasting.

A regional coupled atmosphere–ocean model was used to investigate the effects of mesoscale oceanic anticyclonic eddies (AEs) and cyclonic eddies (CEs) on the atmospheric column above them. The model was simulated from 29 December 2018 to 20 April 2019. The model-simulated surface wind, mean sea level pressure, ocean temperature, and salinity were validated against satellite and in-situ observations. The simulated parameters show a good agreement with the observations. An eddy detection and tracking algorithm was applied to identify mesoscale oceanic eddies from the model output. The thermodynamic properties of the atmospheric column above the detected eddies were analyzed to examine the roles of eddies on the atmospheric column. The Convective Available Potential Energy (CAPE), Convective Inhibition (CIN), water vapor mixing ratio (W_MR), and precipitable water (PW) were computed and compared for AEs and CEs. The vertical profiles of moist static energy (MSE) showed reasonable differences (~10% higher over CEs than AEs) for most of thermodynamic properties except CAPE. The correlation between the relative vorticity of these oceanic eddies and the air column above eddies supported these thermodynamic differences between AEs and CEs. The study demonstrates a role of oceanic eddies in modulating the thermodynamic characteristics of the lower atmospheric column over eddy regions.

A coupled atmosphere–ocean numerical model is used to examine the relative contributions of atmospheric and oceanic processes in developing the Arabian Sea Mini Warm Pool (MWP). The model simulations were performed for three independent years, 2013, 2016, and 2018, through April–June, and the results were compared against observations. The model-simulated sea surface temperature (SST) and sea surface salinity (SSS) bias were less than 1.75°C and 1 psu, respectively; this bias was minimal in the MWP region. Moreover, the model simulated results effectively represented the presence of the MWP across the three different years. The mixed-layer heat budget analysis indicated that the net surface heat flux raised the mixed-layer temperature tendency of the MWP by a maximum of 0.1°C d^-1 during its development phase. The vertical processes exerted a cooling impact on the temperature tendency throughout May and June with a maximum of –0.08°C d^-1. Nonetheless, the decrease of net surface heat flux emerged as the dominant factor for the dissipation of the MWP. Further, four sensitivity numerical experiments were performed to investigate the comparative consequences of the ocean and atmosphere on the advancement of the MWP. The sensitivity experiments indicated that pre-April ocean conditions in years with a strong MWP resulted in a 136 % increase in MWP intensity in years when MWP SST was close to the climatology, which shows the primary role of oceanic preconditioning in determining MWP strength during strong-MWP years. Once the oceanic preconditions are met, the atmospheric conditions of weak-MWP years lead to an 82 % reduction in MWP intensity relative to normal years, highlighting the detrimental impact of atmospheric forcing under such circumstances. Atmospheric conditions, particularly wind, are critical in influencing the spatial evolution and dissipation of the MWP in the southeastern Arabian Sea (SEAS). A wind shadow zone, characterized by less production of turbulent kinetic energy that does not exist during weak-MWP years, facilitates the spatial expansion of the MWP in SEAS during moderate to strong-MWP years.