A Dynamical Initialization Scheme for Binary Tropical Cyclones

Abstract:

A dynamic initialization (DI) scheme for binary vortices (BVDI) is proposed to improve the initial conditions for the simulations of binary tropical cyclones (TCs) using the Weather Research and Forecasting (WRF) model. This BVDI scheme is based on a new hurricane/typhoon DI (HTDI) formulated for the single TC, which is a modification of the DI developed by Cha and Wang (2013) while further introduces the adjustment of initial vortex size and wet bogus vortex.

Two TC cases, i.e., Super Typhoon Saomai (2006) and Tropical Storm Bopha (2006) in Western North Pacific, have been selected as a sample of binary TCs to test the performance of different DI schemes. The adjustment of initial vortex scale in HTDI makes improvements to the evolution of intensity and structure of Saomai. Moreover, the introduced wet bogus vortex ensures the spinning-up of Bopha’s initial vortex. In addition, BVDI not only has the merits of HTDI, but also shows its advantage in reflecting the impact of the interaction on this pair of binary TCs within the initial condition. With that the tracks, intensities and structures as well as their evolutions (e.g. rapid intensification and concentric eyewall) of both Saomai and Bopha could be successfully captured comparing with the observations, which is advantage than other DI schemes. The results indicate that it is necessary to improve the representation of two TCs in the initial conditions and include their interactions in the binary TCs forecast.