1979-2013年东亚中纬度春、夏温带气旋活动特征及其与东北地区同期降水的联系

利用江苏近10 a（2005-2014年）暖季（5-9月）69站逐时降水资料,详细分析了短时强降水的空间分布、年际变化、季节内演变以及日变化特征。分析结果表明：短时强降水空间分布不均,整体上北部比南部活跃,最活跃区均位于沿淮西部,高强度短时强降水多发生在淮北东部,且空间分布集中。近10 a来江苏短时强降水整体呈减少趋势,主要表现为北部地区减少最为显著。短时强降水季节内分布不均匀,以7月最为活跃,高强度短时强降水在8月最为频繁;其逐候分布显示,梅期短时强降水骤增,于7月第2候达到峰值,盛夏期间高强度短时强降水增多,8月第3候达到峰值。江苏短时强降水的日变化整体呈双峰结构,主峰和次峰分别出现在傍晚17时（北京时间,下同）和清晨07时,高强度短时强降水多发于午后;短时强降水日变化存在季节内演变的阶段性特征和地域性差异,其中梅期和盛夏两个高发阶段均呈单峰结构,但梅期峰值出现在清晨,盛夏阶段峰值则出现在傍晚;由南向北,日变化特征由单峰向双峰、多峰演变,在淮河以南地区日峰值大多出现在午后至傍晚,而淮河以北地区多出现在夜间至清晨。

Characteristics of East Asian mid-latitude extra-tropical cyclone activity in spring and summer during 1979-2013 and its linkage with concurrent rainfall in Northeast China

The midlatitude cyclone is a low-pressure vortex with strong baroclinicity that occurs in the mid-to high latitudes in the Southern and Northern Hemispheres.Some studies show that significant changes in the cyclone activity and atmospheric circulation over East Asia have occurred over the past decades.The statistical characteristics of the midlatitude cyclone were analyzed manually in the past,while this method is time-consuming and relies on the subjective experience of researcher.The objective cyclone identification and tracking method is widely used to research on detecting cyclone activities with the development of reanalysis data and numerical model in recent years.The features of precipitation in Northeast China in spring and summer and its relationships with mid-to high latitude circulation systems are well studied.The cold vortex in Northeast China is considered as the key component,while midlatitude cyclone also plays an important role in rainy season.In this study,based on the 4 times daily ERA-Interim mean sea level pressure reanalysis data,using the objective cyclone identification and tracking method,the characteristics of mid-latitude extra-tropical cyclone activity in East Asia in spring and summer during 1979-2013 and its linkage with concurrent rainfall in Northeast China are analyzed.The results show that East Asian mid-latitude cyclones generate in the middle of Mongolia and to the east of Altai Mountains,and move to the north of Heilongjiang province.The cyclone increases gradually to the maximum to the west of Greater Khingan Mountains and dissipates thereafter.The region of cyclone activity in spring is larger than that in summer,and the cyclone is also stronger in spring.While the lifetimes of cyclone are similar in different seasons,the maximum standard deviation of cyclone frequency and intensity are both located in central Mongolia,which indicates that both the most frequent cyclone activity and the greatest variation of cyclone activity happen there.Therefore,Mongolia was selected as the representative area for the abnormal activity of midlatitude cyclone in East Asia.The cyclone numbers in spring and summer in this key area (40-50°N,80-140°E) both display linear decreased trend in the late 35 a.The correlation between the cyclone activity and rainfall in Northeast China is positive in both seasons,but the reasons are different.During the strong cyclone activity years,the cyclonic circulation over Northeast China benefits the increase of spring rainfall,and the increase of summer rainfall mainly depends on the anomalous westerly moist transport.