关键词: 东北地区, 农作物生长季, Palmer干旱指数, 经验正交函数, 大气环流

Abstract: Based on observed data of mean temperature and precipitation from 71 meteorological stations in Northeast China from 1961 to 2009 in crop growing season (from May to September), authors validated Palmer Drought Severity Index (PDSI) to assess the actual drought level, and analyzed its characteristic by using Empirical Orthogonal Function(EOF) method, used the NCEP/NCAR reanalysis data to discuss the circulation background in drought years. The results showed that, (1)PDSI could assess the actual drought level with high ability in crop growing season, but it was easily to exaggerate the seriousness of drought in some years; (2)The accumulative variance contribution ratio of the first three feature vectors reached to 74.9%, and the spatial types of drought in Northeast China could be divided to three patterns: uniform, south-north difference, east-west difference, corresponding with the first three feature vectors individually;(3)During 1961 to 2009,the drought variation mainly existed 9 years and 23 years periodic oscillations in crop growing season, and the drought trend in the next few years might continue to increase; (4)In drought years(PDSI≤-1), the subtropical high presented weak performance in 500hPa height field, Northeast China was the center of positive geo potential height anomaly, indicating that the region was controlled by high pressure, resulting in less rainfall. In terms of 850hPa water vapor flux field, warm wet airflows from southwest and southeast were hardly transported to the Northeast China, and the anti cyclonic circulation and positive divergence also could lead to less precipitation.

Key words: Northeast China, Crop growing season, Palmer drought severity index, EOF, Atmospheric circulation