5—6月东北冷涡持续活动及强度特征

利用1960—2012年5—6月NCEP/NCAR逐日再分析资料，基于冷涡经典定义，采取客观识别方法检索东北冷涡活动过程，根据东北冷涡活动时空变化特征给出东北冷涡持续活动过程标准, 通过冷涡强度指数进行定量化分析，该指数对冷涡持续活动过程具有较好表征意义。冷涡活动强对应5月乌拉尔山阻塞高压、贝加尔湖阻塞高压和6月鄂霍次克海阻塞高压活动频繁。通过强弱指数年合成，得到6月强指数年冷涡系统较深厚，集中于对流层中高层，冷心结构明显，具有一定大气斜压特征; 高层存在冷中心，低层有冷空气活动，中高层西风带呈明显的上游分流和下游汇合特征，分汇流之间呈东北高、西南低的偶极子阻塞形势；弱指数年冷涡系统较浅薄，主要集中在对流层中低层，冷心结构不明显，不存在阻塞形势。

Characteristics of Persistent Activity and Strength of Cold Vortex During May and June in Northeast China

Using the NCEP/NCAR daily reanalysis data from 1960 to 2012, processes of the northeast cold vortex (NECV) are identified objectively. Combined with the characteristic of precipitation, a process standard of NECV persistent activities is proposed, and quantitative analysis is done using the NECV intensity index which has great significance on its persistence. If the NECV is stronger, the activity of the blocking situation over the Ural Mountains and the Lake Baikal in May, and blocking situation over the Okhotsk Sea in June is more frequent. The composition of high and low index year circulation is calculated including the geopotential height, temperature and wind between 1000 hPa and 200 hPa, and two features in the identification zone of NECV are revealed. First, the NECV converge in middle to upper troposphere (from 500 hPa to 200 hPa), having a deep and cold structure. The low pressure system exists form lower troposphere (1000 hPa) to upper troposphere (200 hPa) and a strong baroclinic component exists in geopotential height field. There is cold center in upper troposphere and thermal trough in lower troposphere. In middle to upper troposphere, westerlies have obvious shunt and confluent, and the blocking situation between them shows higher in northeast and lower in southwest. Second, the NECV converge in middle to lower troposphere (from 850 hPa to 1000 hPa), the cold center is shallow and the structure is not obvious. It is straight in the westerlies in middle to upper troposphere (from 500 hPa to 200 hPa) and the blocking situation has vanished. The weak cold center only exists in upper level, and the lower troposphere is controlled by low pressure and warm ridge. This definition of cold vortex persistent activities provides basis and reference for further study on its climate effect and short-term climate prediction.