中国南方大范围持续性低温、雨雪和冰冻组合性灾害事件:客观识别方法及关键特征

组合性灾害事件是指同时出现的若干个天气灾害的组合，它的发生会明显加重致灾程度。本文利用1961～2013年冬季我国南方区域206个台站的日平均温度、日降水量及雨凇资料，建立了冬季大范围持续性低温、雨雪和冰冻组合性灾害事件的客观识别方法，并揭示了三类组合性灾害事件的关键特征。首先，基于低温、雨雪、冰冻天气的强度和面积阈值以及持续天数建立了大范围持续性低温事件、雨雪事件以及冰冻事件各自的客观判识方法。在此基础上界定出了三类常见组合性灾害事件，即低温—雨雪灾害事件（C-RS）、低温—冰冻灾害事件（C-F）以及低温—雨雪—冰冻灾害事件（C-RS-F）。三类组合性灾害事件常见于1月上旬至2月中旬。尽管三类组合性灾害事件在低温和降水等方面有相似之处，但其形成条件却明显不同。充沛的水汽供应和大范围强烈的水汽辐合是低温—雨雪灾害事件和低温—雨雪—冰冻灾害事件发生的关键条件，而逆温层和冷垫则是低温—冰冻灾害事件和低温—雨雪—冰冻灾害事件发生的必要条件。亚洲中高纬大型斜脊系统是低温—冰冻灾害事件和低温—雨雪—冰冻灾害事件的关键环流特征，为强冷空气活动提供了有利环流条件。低温—雨雪灾害事件期间亚洲中高纬则盛行波状环流，有利于适度冷空气活动。在水汽供应和逆温层形成方面，三类组合性灾害事件受控于不同的副热带异常环流系统。孟加拉湾南支槽和南海上空异常反气旋分别是低温—雨雪灾害事件和低温—冰冻灾害事件形成的副热带关键环流系统，而孟加拉湾南支槽和西北太平洋异常反气旋相结合为低温—雨雪—冰冻灾害事件形成的副热带关键环流系统。

Combined Disaster Events of Extensive and Persistent Low Temperatures,Rain/Snow,and Freezing in Southern China: Objective Identification and Key Features

Combined disaster events refer to the combination of several simultaneously occurring weather disasters. In this paper, the daily mean temperature, precipitation, and glaze data of 206 stations over southern China in winter from 1961 to 2013 are integrated to establish an objective method for identifying combined disaster events of extensive and persistent low temperatures, rain/snow, and freezing weather in winter, and the key features of these kinds of combined disaster events are discussed. First, the identification methods for extensive and persistent low temperatures and rain/snow and freezing events are proposed according to the thresholds of their intensities and impact areas. The three most prominent combined disaster events, namely cold-rain/snow (C-RS), cold-freezing (C-F), and C-RS-freezing (C-RS-F) disaster events, are identified. These combined disaster events often occur from early January to mid-February. Although they have similar low temperatures and precipitation levels, their formation conditions are significantly different. Abundant water vapor supply and large-scale strong water vapor convergence are key conditions for the occurrence of C-RS and C-RS-F disaster events, while an inversion layer and cold pad are necessary conditions for the occurrence of C-F and C-RS-F disaster events. The large-scale tilted ridge in mid- and high-latitude Asia is the key circulation feature of C-F and C-RS-F disaster events. It provides favorable circulation conditions for strong cold air activities. During C-RS disaster events, wavy circulation prevails in mid- and high-latitude Asia, which is conducive to moderate cold air activities. The water vapor supply and inversion layer formation associated with the three kinds of combined disaster events are controlled by different subtropical anomalous circulation systems. The southern branch trough over the Bay of Bengal and the anomalous anticyclone over the South China Sea are key subtropical circulation systems for the formation of C-RS and C-F disaster events, respectively, while the combination of the southern branch trough over the Bay of Bengal and anomalous anticyclone over Northwestern Pacific is the key circulation system for the formation of C-RS-F disaster events.