Winnie(1997)和Bilis(2000)变性过程的湿位涡分析

9711号台风Winnie和0010号台风Bills均在中国大陆发生变性，但前者变性后再度加强，而后者变性后减弱消亡。从湿位涡理论出发，对比分析两者的变性过程，结果表明：作为变性台风，Winnie和Bilis均在北上过程中与中纬度西风槽发生作用，但前者与高空槽发生耦合，后者仅接近高空槽底部，没有发生耦合；Winnie变性加强过程表现为一个温带气旋在低层锋区上的强烈发展过程，主要与高层正位涡扰动下传、低层锋区及热带气旋低压环流之间的相互作用有关。Pm湿斜压项增长引起的倾斜涡度发展是登陆热带气旋变性加强的主要因子。在Bills变性过程中，高层无明显的正位涡扰动下传，热带气旋低压环流内无锋区面出现，大气斜压性弱且变化不明显。

MOISTURE POTENTIAL VORTICITY ANALYSIS ON THE EXTRATROPICAL TRANSITION PROCESSES OF WINNIE(1997) AND BILIS(2000)

Typhoon Winnie(9711) and Bilis(0010) underwent extratropical transition (ET) over Chinese mainland but only Winnie re-intensified as an extratropical system. Their ET processes were examined and compared in terms of the Moisture Potential Vorticity u (P_m) perspective. Results show that Winnie enters mid-latitude zone and couples with an upper trough during its ET. Bilis also approaches an upper trough but decouples with it. ET re-intensification is related to the interactions between typhoon remnant circulation and lower layer front zone and P_m anomaly downward transported from the upper troposphere. Especially, slantwise vorticity development caused by the increase of moist baroclinicity is an main factor responsible for Winnie re-intensification. However, there is no frontal zone occurring in Bilis's remnant circulation and downward transportation of the upper P_m anomaly is weak.