Features Of Vorticity Propagation In The Typhoon Region And The Numerical Study On The Landing Track Of Winnie

Sudden changes in the track and intensity of typhoons are major obstacles in further improving the precision degree of typhoon forecasts. After many years effort, scientists at home and abroad have made quiet great progresses in numerical prediction models of tropical cyclones, and meanwhile, generally observed some limitations in the numerical models. How to improve the current numerical model has become a major topic for discussion in several international conferences. The above sudden changes and model improvement are the two aspects of problems strongly interested by the domestic and oversea typhoon researcher communities.This paper investigates the two interrelated problems from the following two parts:First part, a polar coordinate quasi-geostrophic barotropic model, a Cartesian coordinate quasi-geostrophic barotropic model, a quasi-geostrophic baroclinic model, and a quasi-geostrophic barotropic vorticity model under the condition of non-stationary typhoon circulation are designed within the framework of advection dynamics, and systematically dynamic studies on effects of different physical processes on the intensity of typhoons are conducted.Second part, a numerical study on the landing of strong typhoonWinnie (the 11th typhoon in 1997) is performed using the Weather Research and Forecast (WRF) model.The main results can be summarized as the folio wings: In the certain parameter range, the circular shearing basic flow might be able to axisymmetrize the one-wave asymmetric structure of a typhoon and also to transfer the perturbation vorticity in the outer region inwards. The radial advection of vorticity plays a major role in the inward-propagation process of vorticity, and the nonlinear advection of perturbation vorticity may enhance the inward-propagation of vorticity, which results in the locally strengthening of the typhoon circulation.The azimuthally linear advection may results in that the meso-scale vortex of initially circular shape becomes the elongated and spiral vorticity bands; the radial linear advection may transfer the vorticity of the outer region towards the center of the typhoon. The local nonlinear advection increases evidently the inward-propagation of vorticity, and therefore strengthens the typhoon obviously.The non-local nonlinear advection possesses the duality: on one hand, compared with the linear circumstance, it increases the inward-propagation of vorticity, thus favorable to the strengthening of the typhoon; however on the other hand, the inward-propagating vorticity destroys the concentric circle structure of the typhoon circulation, leading to the weakening of the typhoon. Besides, changes in the intensity oftyphoon may remarkably different under the weak and strong radial advection conditions.The WRF (v1.2) system is used to simulate the landing process of Winnie in 1997, and results show that the track, landing time, and landing position of Winnie calculated using the Common Land Model (CLM) and the initial field of 0800 BST on 18th August 1997 are closer to the reality (Fig.4.3) than those in the other 7 experiments, indicating the better forecast and simulation capability of the WRF model than the others.This paper also emphatically discusses the potential applications of the above results in the prediction of intensity and track of typhoons.