冷空气入侵对热带气旋发生发展的影响

The effect of cold air intrusion on the development of tropical cyclone

本文从梯度风方程出发,证明温度梯度增强对涡度起到增强作用.因此当冷空气侵入热带气旋外围时,只要没有破坏热带气旋的暖心结构,就会引起温度梯度的增长,从而促进热带气旋的发生发展.本文采用NCAR/PSU研制的非静力中尺度模式MM5,研究北半球冷暖空气入侵在热带气旋形成和加强过程中的作用.通过研究冷暖空气对热带气旋发展影响的试验发现,冷暖空气在入侵热带气旋外围时,最主要改变的是外围的环流场.北半球冷空气的入侵将会增强热带气旋北面的北风,形成指向热带气旋中心的推力,即辐合增强,暖空气入侵减弱北面的北风,形成背向热带气旋中心的拉力,即辐合减弱.由于拉力作用,一方面把边界上由于冷空气入侵而生成的能量往热带气旋中心输送,另一方面导致温度梯度的增加.因此从天气学形势来看,在热带气旋发生发展的过程中,北方的冷高压将会增强热带气旋北面的风速,从而导致热带气旋的增强;南半球澳高的增强,将使越赤道气流增强,热带气旋南面的风速也因此增强,从而引起热带气旋的增强.

It is confirmed through the gradient wind equation that the rising of temperature gradient will cause the rising of vorticity. This means that cold air will promote the development of tropical cyclone if the warm--core of the tropical cyclone has not been destroyed. A number of numerical experiments are designed by changing lateral boundary conditions with cold air or warm air. Numerical results show that the major change is the environmental circulation of tropical cyclone when the surges immerge into the outmost of the tropical cyclone. The warm air from the Northern Hemisphere will reduce the north wind of the tropical cyclone. The pulling force away from the center of the tropical cyclone is formed, which weakens the mass convergence. On the contrary, the cold air from the Northern Hemisphere will intensify the north wind of the tropical cyclone. The pushing force to the center of the tropical cyclone is formed, which intensifies the mass convergence. Because of the pushing force, on the one hand, the energy is transported to tropical cyclone, which is generated for the intrusion of the cold air; on the other hand, the temperature gradient is intensified. In the weather system, the cold anticyclone in the north and the Australian cold air activity will intensify the tropical cyclone in the Western Pacific.