Climatological and Seasonal Variations of the Tropical Cyclone Genesis Potential Index Based on Oceanic Parameters in the Global Ocean

This study investigates the global performance of the tropical cyclone(TC)genesis potential index based on oceanic parameters(GPI_(ocean))proposed by Zhang et al.(2016).In six major TC formation basins,GPI_(ocean)can represent the seasonal variations of TC genesis over most basins,except for the North Indian Ocean(NIO).The monthly climatological GPI_(ocean)shows only a single peak in the NIO,which cannot describe the bimodal pattern of the annual cycle of TC genesis.To determine the cause of the poor performance of GPI_(ocean)in the NIO,the relative contributions of different parameters related to GPI_(ocean)are calculated and compared with those related to the genesis potential index developed by Emanuel and Nolan(2004)(GPI04).Results show that the net longwave radiation on the sea surface is responsible for the single peak of TC genesis in the NIO in boreal summer.Compared with GPI04,vertical wind shear is not involved in GPI_(ocean).Vertical wind shear is the dominant factor inhibiting TC genesis in the NIO in boreal summer.Therefore,the absence of vertical wind shear in GPI_(ocean)results in the failure of the annual cycle of TC genesis in the NIO.