1979—2018年5—8月中国东北冷涡建立的客观识别方法及变化特征

东北冷涡是中国东北地区重要的天气系统，采用欧洲中期天气预报中心（ECMWF）提供的ERA-Interim一日4次再分析资料，并改进现有的客观识别方法，将分析天气图的思路运用于对冷涡的客观识别中，检索出1979—2018年夏季（5—8月）516个东北冷涡过程。为了研究冷涡生成位置的差异，以45°N线为X轴，125°E线为Y轴将研究区划分为4个象限。结果表明:夏季东北冷涡生成位置以第2象限（西北部）最多，第4象限（东南部）最少，冷涡以向东移动为主。夏季东北冷涡的平均生命期为3.2 d，各象限生成的冷涡平均生命期有较大差异，第2象限最长，平均约为3.5 d；第4象限最短，平均约为2.9 d。72.1%的冷涡过程生命期少于4 d。夏季各月第2象限生成的冷涡频数均远多于其他3个象限，且具有很明显的逐月递减的季节内变化特征。东北冷涡的生成位置和频数具有明显的年代际变化，5月，1998—2007年偏北，2008—2018年偏南；6月，1980—1998年南移，2008—2018年北移，1993—2003年以偏东为主，2004—2018年以偏西为主；7月，1998—2010年北移，1985—2000年偏西，2005—2012年偏东；8月，2002—2010年偏北，2009—2018年偏东。就频数而言，特别是第2象限生成的冷涡，其年代际变化在季节内存在明显不一致，5月，1979—1985年冷涡偏多，1986—1992年冷涡偏少；6月，1979—1992年偏多，1993—2018年偏少；7月，1980—1991年偏多，1992—2000年偏少。 

Objective identification method and variation characteristics of the Northeast China cold vortex from May to August of 1979—2018

Northeast China cold vortex (NECV) is an important weather system in Northeast China. Based on the ERA-Interim four times daily reanalysis data provided by ECMWF, the existing objective identification method is improved and the idea of weather map analysis is applied to the objective identification of cold vortex. 516 Northeast China cold vortex processes in the summers (May to August) from 1979 to 2018 are extracted in this study. In order to study the difference in the NECV initial position, the active region of the NECV is divided into four quadrants with 45°N as the X-axis and 125°E as the Y-axis. Results show that in summer, the frequency of NECV formation is the highest in the second quadrant (northwest) and the lowest in the fourth quadrant (southeast). The NECVs are mainly moving to the east. The average persistence time of the NECV in summer is 3.2 d, and the persistence times are quite different for NECVs generated in different quadrants. The longest persistence time is found for NECVs generated in the second quadrant (3.5 d on average) while the shortest is found for those generated in the fourth quadrant (2.9 d on average). 72.1% of the NECVs have a lifespan less than 4 d. The frequency of the NECV generatation in the second quadrant in each month of the summer is much more than that in the other three quadrants, and decreases month by month, demonstrating an obvious characteristic of intraseasonal variation. The initial position and the frequency of the NECV both have obvious interdecadal variation characteristics. In May, the NECV initial position is located further north from 1998 to 2007 and further south from 2008 to 2018. In June, it moves southward from 1980 to 1998 and northward from 2008 to 2018. It is also located further east from 1993 to 2003 and further west from 2004 to 2018. In July, it moves northward from 1998 to 2010, westward from 1985 to 2000 and eastward from 2005—2012. In August, it is located further north from 2002 to 2010 and further east from 2009 to 2018. In terms of frequency, especially in the second quadrant, the interdecadal variation of the NECV is obviously inconsistent within the season. There are more NECVs from 1979 to 1985 and fewer from 1986 to 1992 in May; more from 1979 to 1992 and fewer from 1993 to 2018 in June; more from 1980 to 1991 and fewer from 1992 to 2000 in July.