2008年1月中国南方低温雨雪期间异常阻塞高压事件的多尺度动力过程分析

2008年1月，中国南方发生了罕见的低温雨雪灾害，造成这次灾害的关键系统之一是乌拉尔山以东地区的异常阻塞高压（阻高）。基于NCEP再分析资料，利用新发展的多尺度子空间变换和重构分析了这一期间阻高的多尺度特征，发现其源头来自欧洲地区，强度减弱后东移，在乌拉尔山—贝加尔湖地区重新增强并得以维持相当长的时间。结果表明，两次阻高过程本质上是同一过程在不同阶段的表现。为探讨上述过程的动力学机制，利用基于多尺度子空间变换的局地多尺度能量分析方法以及正则传输理论对其进行了分析，发现此次异常阻高过程源自32 d以下尺度系统的动能强迫，具体地说，能量来自32 d以下尺度系统向32—128 d低频尺度系统的正压正则传输，而且这种正则传输在阻高环流的东、西两侧不对称，西侧在强度上远大于东侧。分析表明，上述非对称的强迫作用由动能空间输运来平衡，平流将西侧获得的32—128 d低频尺度动能向东侧输运，以此来维持阻高环流的整体稳定和均一。上述两种内部的物理过程是高压环流在东移的过程中得以重新增强并长时间维持的机制。 

A study of the multiscale dynamical processes underlying the blocking high that caused the January 2008 freezing rain and snow storm in southern China

In January 2008, an unusual mid-high latitude blocking high pressure system caused a record-breaking freezing rain and snow storm event in southern China. Using a recently developed functional analysis tool, i.e., the multiscale window transform (MWT), the system is investigated to better understand the underlying mechanisms. By examining the multiscale pattern that is reconstructed, the blocking high is found to originate from the European region; it then became weak and moved eastward. The weakened high, however, regained energy over the Mt. Ural-Lake Beaikal region, and persisted henceforth. A new finding is that the previously identified two blocking highs are essentially one single blocking high in two stages. The MWT-based localized multiscale energetics analysis and the theory of canonical transfer were used to investigate the dynamical processes underlying the anomalous event, and find that it was driven by processes on time scales less than 32 d. Specifically, its energy came from the barotropic canonical transfer from less than 32 d scale window to 32-128 d scale window. The canonical transfer was asymmetric about the blocking high, much stronger in the west than in the east. This asymmetry was balanced through a west-to-east energy transport on the 32-128 d scale window to maintain a quasi-stable and homogeneous pattern. The above two internal processes led to the rejuvenation and stagnation of the blocking high, causing the severe, disastrous weather in southern China.