Comparative Analysis Of Tropical Cyclone Potential Generation Indices And Improvements In The Northwest Pacific

The genesis potential index(GPI)of TC includes dynamic and thermodynamic parameters that are necessary conditions for TC genesis.In this study,the performances of several existing GPIs(GPI_EN,GPI_MW,GPI_CY,GPI_TC,GPI_ZW and GPI_ZZ)are evaluated against the observed TC genesis frequency(TCGF)during 1979-2017 in the North Atlantic and western North Pacific(WNP).Results show that the existing GPIs can reproduce the climatological distribution and annual cycle of TCGF over the two basins fairly well,as well as the interannual variability of TCGF in the North Atlantic very well,but fail to reproduce the interannual variability of TCGF in the WNP.Based on the best-track TC data and the ERA-Interim reanalysis data during 1979–2017,a modified GPI is developed for the WNP.This modified GPI considers the earth vorticity(Coriolis parameter)and relative vorticity separately instead of the use of the absolute vorticity and discards relative humidity used in most of the existing GPIs.Compared with the existing GPIs,the modified GPI can reproduce not only the climatological distribution and annual cycle,but also the interannual variability of TCGF in the WNP,especially in the southeastern WNP.The modified GPI are also evaluated with NCEP/NCAR,JRA-55 and ERA5 reanalysis,showing consistent and even better performance in reproducing the interannual variability of TCGF with JRA-55 or NCEP/NCAR reanalysis datasets.Besides,the modified GPI performs better than the existing GPIs in reproducing the interannual variability of both intense and weak TC.