热带气旋的温带变性过程对下游影响的研究进展

热带气旋(TC)在向高纬度地区移动过程中往往会转变为温带气旋，称之为温带变性(ET)过程。ET过程涉及到热带系统与中纬度环流的复杂相互作用，并对局地系统直至大范围环流均产生影响，这种影响甚至向下游延伸到半球的尺度。由于ET过程及其下游影响给中纬度地区带来严重灾害性天气，而对其的预报一直是一个难题，因而关于此问题的科学研究和业务预报是近年来国际上的一个热点，国内的有关工作也已开展。从TC在ET过程中与中纬度环流的相互作用、ET过程对中纬度下游环流的影响和ET过程及其下游影响的数值预报三个方面总结和分析了近年来国内外的有关研究进展，为国内学术界进一步开展相关研究提供参考。主要进展包括:(1) TC高层出流输出低位涡(PV)空气改变温带上层结构以及TC环流直接作用于中纬度流是TC-中纬度流相互作用的主要方式；TC相对于上游槽的位置对ET过程及其下游影响很关键；各种物理过程在相互作用中起到不同的作用；(2) TC所激发的Rossby波在与急流相联系的上层PV梯度上向下游频散是下游发展的主要方式；下游发展具有显著的边界俘获和上下层耦合发展的特征；(3) 目标观测、集合预报和变分同化等技术的发展提高了ET及其下游影响的数值预报水平。 

RESEARCH PROGRESS ON THE IMPACT OF EXTRATROPICAL TRANSITION OF TROPICAL CYCLONE ON THE DOWNSTREAM FLOW

As a tropical cyclone(TC) moves northward, it often transforms into an extratropical cyclone, which is known as an extratropical transition (ET) process. An ET process involves the complex interaction between the tropical systems and the midlatitude flows, which not only changes the local atmospheric state around a TC but also affects the atmospheric circulations over a larger region. Especially, the downstream impacts are much more obvious. ET and its downstream impact often lead to serious disasters in the midlatitudes, and its accurate forecast is still difficult. Therefore, scientific research and operational forecasts concerning the ET process and its downstream impact become current hotspots. In this work, the international and domestic progress in the interaction of TCs with midlatitude flows, the downstream impacts of ET systems, the numerical forecast of the downstream impacts are summed up and analyzed.