长江中下游地区冬夏干湿韵律特征分析

Analysis of dry/wet rhythms in winter and summer precipitations over the mid-lower reaches of the Yangtze River Basin

中文关键词:  干、湿韵律现象  长江中下游降水  大气环流  冬夏季风

英文关键词:Dry/wet rhythms  Precipitation in the mid-lower reaches of the Yangtze River Basin  Atmospheric circulation  Winter and summer monsoons

中文摘要:

      通过分析中国160站1952—2013年的月平均降水观测资料,揭示了长江中下游地区冬季和夏季降水间存在显著的韵律现象,即当该地区冬季降水异常偏少(偏多)时,次年夏季降水也趋于异常偏少(偏多),这里称之为干(湿)韵律现象。对干、湿韵律年大气环流背景的分析结果显示,干韵律年和湿韵律年对应的环流形势基本相反:在干(湿)韵律年冬季,东亚地区500 hPa位势高度距平呈现西高东低(东高西低)的分布型,中国南方东部主要受偏北(南)风异常控制,这不利(有利)于低纬度暖湿气流向长江中下游地区输送,导致该地区冬季降水异常偏少(多);在次年夏季,西北太平洋副热带高压异常偏弱(强),不利(有利)于西南暖湿气流向中国东部地区输送,使得长江中下游地区夏季降水也异常偏少(多)。研究进一步指出,长江中下游地区的冬夏干、湿韵律现象与东亚冬夏季风活动的强度密切相关。干、湿韵律现象多在东亚冬夏季风强度变化一致的情况下出现:冬、夏季风一致偏强时多导致干韵律现象,而一致偏弱时易导致湿韵律现象。

英文摘要:

      By analyzing the monthly mean gauge precipitation data from the 160 stations in China during 1952-2013, this paper reveals a significant rhythm phenomenon in winter and summer precipitations in the mid-lower reaches of the Yangtze River Basin. That is, if in winter there is less (more) precipitation than the normal over this region, precipitation in the following summer tends to be less (more) as well. Such a phenomenon is referred to as dry/wet rhythms. It is showed that the atmospheric circulation anomalies between dry and wet rhythm years are basically contrary to each other over the East Asia-Northwest Pacific region. For example, in the winters of wet rhythm years, 500 hPa height anomalies are mainly negative in the continental China, but positive in its east ocean, which yields that eastern South China is mainly dominated by southerly anomalies, and thus the mid-lower reaches of the Yangtze River Basin tends to be more rainy. In the following summers, the western North Pacific subtropical high is preferentially intensified, which tends to induce anomalous southerly wind and hence increase precipitation in the mid-lower reaches of the Yangtze River Basin. The results further indicate that the winter-summer dry/wet rhythms are intimately associated with intensity of the winter and summer monsoon activities in East Asia; i.e., the wet rhythms usually correspond to both weaker winter and summer monsoons, while the dry rhythms to both stronger winter and summer monsoons.