Spatial Characteristics and Evolution Mechanisms of the Indian Ocean Tripole Mode and Its Impact on Rainfall Patterns Over India

The IOT mode is an interannual climate pattern in the Tropical Indian Ocean (TIO), characterised by negative SSTA in both the eastern and western TIO, and positive SSTA in the south-central TIO. Distinct from the IOD, which accounts for 10% of SSTA variability in the TIO, the IOT explains 8% of this variance. This study reveals that strong south-westerly wind anomalies along the Somali coast and Arabian Sea associated with a positive IOT drive intense surface cooling, which spreads across the western basin through lateral advection. A typical positive IOT enhances monsoon winds over northern India, leading to increased rainfall across the Indo-Gangetic Plains, while deflecting monsoon winds further south over the southern peninsula, resulting in reduced rainfall there. Additionally, a cyclonic wind anomaly in the Bay of Bengal dampens winds over regions of northeastern India, suppressing summer monsoon rainfall. The findings underscore the significant role of the IOT in modulating monsoon rainfall and its spatial distribution. This study highlights the IOT's potential to enhance understanding of monsoon variability, and its incorporation into predictive models could improve climate resilience in monsoon-dependent regions.