Numerical Simulation of the Effect of Subtropical Anticyclone on the Evolvement of Potential Vorticity of Landfall Typhoon on Isentropic Surface
副热带高压对登陆台风等熵面位涡演变影响的数值模拟研究

Typhoon Winnie (1997) is taken as an example, and the entire process including initial weakening, extratropical transition and redeveloping after landfall is reappeared using the MM5 model. Using the piecewise potential vorticity (PV) inversion advanced by Davis et al.(1996), the authors pick out the PV break with the physical meaning of subtropical anticyclone and change its intensity to get different initial fields. The conservational character and the adiabatic and diabatic effect with different intensity of eastern subtropical anticyclone during the entire process are explored by using the Ertel potential vorticity budget equation on isentropic surface The results show that transportation of high PV from the upper to lower troposphere makes local PV increase in the lower troposphere, the divergence is favorable to redeveloping of typhoon. Because of the existence of friction and diabatic heating, the local change of PV is mainly decided by the horizontal advection of PV, vertical advection of PV, vertical differential of heating. The conservational character undergoes the weakening and redeveloping in the area of typhoon during the extratropical transition. The vertical advection of PV describes the local change of PV in the middle troposphere better and the vertical differential of heating is better for that in the upper and lower troposphere. The stronger subtropical anticyclone may quicken the northward speed and extratropical transition of typhoon, and the transportation of upper PV is earlier and the intensity is stronger. The destroying and rebuilding of PV conservation is also earlier. The whole-level negative vertical advection of PV is also weaker and the positive effect of vertical differential of heating on local increasing of PV in the lower troposphere is larger and last longer.