Verification of downscaling framework for interannual variation of tropical cyclone in Western North Pacific

Abstract

The downscaling framework, which is originally proposed by Emanuel et al. (2008), is modified to improve the interannual variation of the tropical cyclone features in Western North Pacific (WNP). The original framework, which utilizes axisymmetric model driven using monthly mean atmosphere and ocean variables, well reproduced interannual variation of tropical cyclone indices over North Atlantic while there is room for further improvement over WNP. The modified treatment of relative vorticity plays an essential role for improving interannual variation of genesis counts and power dissipation index in WNP. In this update, we introduced probability of cyclogenesis special to WNP which is a priori calculated using monthly mean 850-hPa level relative vorticity and best track. The result suggests that the monthly mean relative vorticity represents a potential of characteristic initiating disturbance in WNP such as monsoon trough and intraseasonal variation. Another experiment shows increased influence of vertical wind shear in middle troposphere improves the distribution of tropical cyclogenesis in WNP while it slightly deteriorates the interannual variation of genesis count.