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Characteristics of Persistent Activity and Strength of Cold Vortex During May and June in Northeast China
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摘要: 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。Abstract: 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.
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图 1 1960—2012年5—6月东北冷涡活动年际变化特征
(a) 发生频次，(b) 活动日数
Fig. 1 Annual variation of NECV activity during May and June from 1960 to 2012
(a) occurrence frequency, (b) the number of activity days
图 2 1960—2012年5—6月东北冷涡活动随冷涡过程持续时间变化
(a) 发生频次，(b) 活动日数
Fig. 2 The variation of persistence time of NECV activity with different variables during May and June from 1960 to 2012
June from 1960 to 2012 (a) occurrence frequency, (b) the number of activity days
图 3 5—6月东北冷涡活动空间分布特征
(a) 随经度变化, (b) 随纬度变化
Fig. 3 The spatial distribution of NECV activity during May and June
(a) variation with longitude, (b) variation with latitude
图 4 5—6月东北冷涡持续活动过程与东北冷涡过程日数对比
Fig. 4 Comparison between the number of NECV persistent activity days and the number of NECV activity days during May and June
图 5 1960—2012年东北冷涡持续活动过程期间500 hPa高度场合成 (单位：gpm)
(a)5月合成，(b)6月合成
Fig. 5 Composition of 500 hPa geopotential field of NECV persistent activities from 1960 to 2012(unit:gpm)
(a) in May, (b) in June
图 6 东北冷涡指数与500 hPa 5月高度场 (a)、6月高度场 (b)、5月温度场 (c)、6月温度场 (d) 相关分布
Fig. 6 Correlation coefficients between NECV intensity index and 500 hPa geopotential height in May (a), 500 hPa geopotential height in June (b), 500 hPa temperature in May (c), 500 hPa temperature in June (d)
图 7 1960—2012年6月强弱冷涡指数年高度场 (阴影)、温度场 (虚线，单位：℃) 和风场 (矢量) 合成
Fig. 7 Composition of height (the shaded), temperature (the dotted, unit:℃) and wind (the vector) fields of NECV in different strength in June from 1960 to 2012
表 1 1960—2012年5—6月东北冷涡活动统计特征
Table 1 Statistical characteristics of the northeast cold vortex (NECV) during May and June from 1960 to 2012
时段 日数/d 频次 所占比例% 平均频次 平均日数/d 冷涡平均维持日数/d 5—6月 1710 388 52.9 7.32 32.3 4.58 5月 757 181 46.1 3.42 14.3 4.18 6月 953 207 59.9 3.91 18.0 4.60 
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