副热带高空急流强弱和走向的变动对我国南方冬季雨雪冰冻灾害的作用

Diagnosis, dynamic analysis, and numerical simulation are adopted in this project with the aim to study the roles of the intensity and orientation variations of the subtropical upper level jet streams in the occurrence, development and maintenance of the freezing rain/heavy snowfall disasters in southern China during winter. Firstly, the effects of the transverse vertical circulations change induced by the intensity and orientation variations of the subtropical upper level jet streams on the disasters are analyzed. Secondly, the influences of the intensity and orientation variations of the subtropical upper level jet streams on the trough in the middle and low troposphere associated with southward motion of the cold air are revealed by calculating and contrasting the terms in eddy kinetic energy equation. Finally, the impacts of the coupling of the subtropical upper level jet streams, the transverse vertical circulations and the mid-low level trough in the disasters are tested numerically by WRF model. All these studies will provide scientific basis for deep understanding and diagnosing this kind of disaster weather process, and offer new ideas and methods to the disasters prediction.

本申请项目采用资料诊断、动力分析和数值模拟相结合的研究方案，研究副热带高空急流强弱和走向的变动对我国南方冬季雨雪冰冻灾害的作用。首先，研究副热带高空急流强弱和走向的变动引起的次级环流的变化对灾害的影响。其次，通过计算扰动动能方程各项，揭示副热带高空急流强弱和走向的变动对与冷空气南下有关的中低层槽的影响。最后，模拟副热带高空急流强弱和走向的变动、引起的次级环流的变化和中低层槽的变化的偶合对灾害的作用。本研究旨在为深入理解并诊断分析我国南部冬季雨雪冰冻灾害过程提供科学依据，并为其预测提供思路和方法。

利用欧洲中期预报中心再分析数据和中国气象局提供的降水数据分析了2008 年1月到2月初高空急流以及高原异常热源对我国南方雨雪冰冻灾害的影响，并给出了高空急流变化以及高原热源变化可能的原因。东亚急流与西亚急流靠近时，它们之间的次级环流相互作用，有利于我国南方冬季雪灾的发展；靠近后控制我国上空的急流变成倾斜急流，高空急流的倾斜也同样有利于雪灾的发展。这两条急流的靠近和形变主要是由扰动位势平流决定。高原西侧异常热源移动到我国上空，在我国上空形成高压脊，它的形成阻碍了北方冷空气向南输送，并聚集在脊后，为后期灾害的爆发提供足够的冷空气。同时，移动到我国上空的热源使高空急流变得平直，不利于垂直运动的产生。异常热源的东移主要是由平流、静力稳定和绝热加热引起的。