Impact of Indian Ocean Dipole on the Arabian Sea tropical cyclone activity

Tropical cyclone (TC) activity in the Arabian Sea has increased notably in recent years. However, the relationship between TC activity in the region and major climate modes is relatively unexplored. This study examines the influence of three dominant modes of climate variability- Madden Julian Oscillation (MJO), El Niño Southern Oscillation (ENSO), and Indian Ocean Dipole (IOD) on TC activity in the Arabian Sea during the post-monsoon season. The results indicate that the IOD exerts a relatively stronger influence on TC activity in the Arabian Sea compared to the MJO and ENSO. Further, we document the various pathways and mechanisms through which the IOD modulates TC activity. During positive IOD years, anomalous northwestward surface winds induced by the zonal sea surface temperature gradient enhance Ekman convergence in the Arabian Sea. This process elevates the sea surface height, deepens the thermocline, and enhances downwelling, thereby increasing upper ocean heat content in the region. Additionally, during IOD events, a reduction in atmospheric winds at both lower and upper-levels leads to a weakening of vertical wind shear over much of the Arabian Sea. These combined oceanic and atmospheric conditions favor the development and intensification of TCs during IOD. Our findings suggest a robust linkage between IOD and TC activity in the Arabian Sea. Given the increasing frequency of intense IOD events in recent years, this study has significant implications for enhancing the predictability and understanding of TC activity in the Arabian Sea, particularly in the context of an evolving storm environment.