Abstract
This study examines the Indian Ocean Basin Mode (IOBM) associated tropical cyclone (TC) activity in the north Indian Ocean (NIO) and western North Pacific (WNP), categorizing the three types of warm (W1, W2, andW3) and cold (C1, C2, and C3) IOBM events from 1980 to 2021. Type 1 refers to the decay of the IOBM without transferring to the Indian Ocean Dipole (IOD), while Type 2 is the conversion of positive IOBM to negative IOD or vice versa. Type 3 is a warm (cold) IOBM event transforming into positive (negative) IOD. The findings reveal that during W1 events, there is a southward shift of TC genesis locations over the NIO in October–November (OND), whereas TCs forming during W2 and C3 events predominantly occur over the Bay of Bengal. Over the WNP, the TC genesis locations from July to September (JAS) shifted northward in W1 and W2 events, resulting in less intense TCs. Conversely, TCs in W3 events shifted southeastward, leading to more intense TCs. The analysis using the genesis potential index (GPI) further demonstrated an enhancement of TC genesis in the southeastern WNP during W3 and C2 years, while a suppression of GPI is observed during W2 and C3 years. Most importantly, increased low-level relative vorticity and higher mid-tropospheric relative humidity facilitate the enhancement of TC genesis in the southeastern WNP during W3 events. Overall, findings provide a detailed, holistic picture of the intricate relationships between IOBM-influenced large-scale factors and the genesis of TCs across the WNP and NIO regions.
Keywords
Genesis Potential Index, Indian Ocean Basin Mode, North Indian Ocean, tropical cyclones, Western North Pacific