Extensive Cold-Precipitation-Freezing Events in Southern China and Their Circulation Characteristics

Abstract

Concurrence of low temperature, precipitation and freezing weather in an extensive area would cause devastating impacts on local economy and society. We call such a combination of concurrent disastrous weather “extensive cold-precipitation-freezing” events (ECPFEs). In this study, the ECPFEs in southern China (15°–35°N, 102°–123°E) are objectively defined by using daily surface observational data for the period 1951–2013. An ECPFE in southern China is defined if the low temperature area, precipitation area and freezing area concurrently exceed their respective thresholds for at least three consecutive days. The identified ECPFEs are shown to be reasonable and reliable, compared with those in previous studies. The circulation anomalies in ECPFEs are characterized by a large-scale tilted ridge and trough pairing over mid- and high-latitude Eurasia, and the intensified subtropical westerlies along the southern foot of the Tibetan Plateau and the anomalous anticyclonic circulation over the subtropical western Pacific. Comparative analysis reveals that the stable cold air from the north and the warm and moist air from the south converge, facilitating a favorable environment for the concurrence of extensive low-temperature, precipitation and freezing weather.

摘要

大范围低温雨雪冰冻事件(Extensive Cold-Precipitation-Freezing Event,以下简称 ECPFE)是冬季中国南方地区频发的气候灾害之一。它的主要特征是大范围低温、降水(雨雪)和冻雨同时发生。它对国民经济和社会生产造成巨大影响。本文利用1951-2013年的逐日地面观测资料和再分析资料,客观界定了中国南方地区(15°-35°N, 102°-123°E)的ECPFE,并分析其环流特征。当低温面积、降水面积和冰冻面积同时超过各自的阈值,并至少持续三天,则确定发生一次中国南方地区的ECPFE。1951-2013年间共确定109次ECPFE。与以前的主观界定结果相比,本文所确定的ECPFE是合理的、可靠的。对ECPFE期间的环流进行研究,发现,ECPFE发生于中纬度和低纬度环流特殊配置时期:(1)中高纬度的大型斜脊和斜槽引导冷空气从西路侵入中国南方,形成低层的冷垫;(2)活跃南支槽和西太平洋反气旋异常导致中国南方盛行南风异常,有利于暖湿空气向中国南方输送,有利于逆温层和冻雨的形成;(3)中高纬度和副热带环流异常必须处于对峙的状态;来自北方的冷空气和来自南方的暖湿空气交汇,并且长时间维持,形成了大范围低温、降水和冰冻天气的有利环流条件。