SVD揭示的东亚地区低频振荡强度与中国夏季降水的联系

ASSOCIATION OF 30-60-DAY INTRASEASONAL OSCILLATION INTENSITY IN EASTERN CHINA WITH THE SUMMERTIME RAINFALL IN CHINA AS REVEALED BY SVD ANALYSIS

利用1978—2007年NCEP/NCAR再分析资料、中国160站月平均降水资料,采用SVD方法分析了东亚地区低频振荡强度与中国夏季降水异常的联系。结果表明:东亚地区低频振荡强度年际变化与中国夏季降水异常分布密切相关,其前3个模态分别对应的降水型:江淮型、华南型及长江中下游型。根据前3个模态分别定义低频振荡强度指数,选定异常年份对相关要素进行合成差值分析发现:"江淮型"高低指数年西太平洋海域的低频环流、对流、热源呈现南北向的反位相分布特征,江淮流域位于异常较强的两个相反性质的低频气团系统之间的气流交汇带;而东亚副热带地区东西向系统波动对"华南型"降水有重要作用,华南地区的局地对流加热对降水异常的发生影响显著;"长江中下游"降水型不仅受西太平洋海区低频环流、热源的影响,热带中太平洋的对流活动与长江中下游地区降水也有重要联系。

By using NCEP/NCAR reanalysis and monthly precipitation data at 160 stations in China during the period 1978-2007,we have studied the relationship between the intensity of intraseasonal oscillation （ISO） over East Asia and the summertime rainfall anomalies in China.The results show that there is a close connection between the interannual variability of ISO intensity in East Asia and the abnormity of summer rainfall in China.The first three modes of SVD reanalysis correspond to three precipitation types of the Yangtze-Huaihe River valley （type 1）,South China （type 2） and the middle and lower reaches of Yangtze River （type 3）.Three indexes are defined respectively for the ISO intensity from the results of the first three modes of SVD,and the anomaly years are chosen according to the indexes.A composite difference analysis is then performed on correlative factors.It is shown that the low-frequency circulation,convection and non-adiabatic heating in Western Pacific Ocean exhibit an anti-phase distribution for type 1 between two abnormal strong low-frequency out-of-phase systems.East-to-west fluctuations of the subtropical East Asia play an important role in type 2,and local diabatic heating in South China also influences the abnormal rainfall.Type 3 is influenced not only by the low-frequency circulation and diabatic heating in Westem Pacific Ocean,but also by the activities of convection in tropical Eastern Pacific.