台风变性过程中下游环流发展的个例对比研究

Case Comparing Study of Downstream Circulation Development during Typhoon Extratropical Transition

台风在温带变性过程(Extratropical Transition,ET)中与中纬度系统的相互作用会引起下游环流的发展,选取3个台风个例,通过分析涡动动能收支和理想化模拟实验对其下游发展机制进行研究。3个台风的变性过程所引起的下游发展都具有共同的机制,即首先在上层下游有脊和槽先后发展,随后激发低层涡旋生成,并与之耦合,形成一个贯穿整个对流层的深厚气旋系统。促使下游脊生成和发展的非地转位势通量源于台风,高层系统向下输送的垂直非地转位势通量在低层辐合,使得涡旋在低层发展。模拟实验表明,台风出流向中纬度急流区域输送低位涡(Potential Vorticity,PV)空气,使得其PV梯度增大和斜压性增强,从而激发了Rossby波在急流中生成并沿之向下游传播,而下游槽脊对引起更下游波型的发展也是通过Rossby波的频散而达成。

The interaction between extratropical transition process and the mid-latitude jet system stimulates the downstream development. In this paper, three typhoon cases were selected to study their downstream develop- ment mechanism through the analysis of the eddy kinetic energy budget and the idealized simulations. The results of Chen＇ s work to the Pacific region were examined. The results were consistent with the results of Chen＇ s Atlantic hurricane Case. ET downstream at the upper levels generated first eddies, and the disturbances triggered the low level eddy development. Then the upper and the lower coupled and formed a deep cyclone system throughout the whole troposphere. The ageostrophic geopotential flux promoted the formation and development of the downstream ridge from the typhoon. Vertical ageostrophic geopotential flux transferred energy from upper downward that conver- gence happened in lower, which stimulated the lower-level cyclone development. Simulation results showed that, in the process of ET, TC outflow transported low potential vorticity to mid-latitude jet, which enhanced the PV gradi- ent and the baroclinic. Then, it is inspired the Rossby wave in the jet and propagated downstream. The formation of downstream ridge-trough couple and development of the further wave was the spread to the downstream through the Rossby wave.