The Role of Tropical Cyclone Seeds on Modulating the Seasonal Cycle of Tropical Cyclone Frequency in the North Indian Ocean

This study investigates the seasonal cycle of tropical cyclones (TCs) in the North Indian Ocean (NIO) using a multi-stage framework of tropical cyclogenesis that considers the TC seeds and TCs separately. We find that the May-June (MJ) pre-monsoon season features fewer TC seeds (similar to 23) with high survival rates (SR, similar to 2.8%), while the post-monsoon season October-November (ON) shows abundant TC seeds (similar to 66) with low SR (similar to 1.8%). Genesis potential indices (GPIs), which combine key environmental factors, capture the TC seed numbers and spatial distribution but fail to explain SR differences between seasons. Composite analysis reveals that MJ season TC seeds exhibit more intense convection, suggesting additional sources of instability not included in current GPIs, potentially related to horizontal gradient of moisture. These findings highlight the importance of considering both TC seed numbers and SR when investigating TC frequency in the NIO and show GPIs' limitations that focus solely on local environmental variables.