【摘要】 中高纬度气压系统的异常对东亚夏季风年代际变化具有重要的影响。中蒙地区平均海平面气压和500 hPa位势高度距平异常与东亚夏季风年代际变化的负相关系数分别达-0.67 和-0.69, 远远超过了99.9%信度。在中高纬度地区气压系统异常表现为距平低压的1960—1976 年期间, 东亚季风区盛行较强的偏南风, 增强了东亚夏季风, 造成华北地区多雨; 而在中高纬度地区气压系统异常为距平高压时的1977—2000年, 其东部的偏北风阻止了南来水汽的往北输送, 减弱了东亚夏季风强度, 使华北地区降水明显减少, 江淮流域降水增多。100 hPa位势高度的距平场呈偶极子型分布, 表现为东高西低时东亚夏季风偏强, 西高东低时东亚夏季风偏弱, 这一现象在东亚夏季风年代际变化中的影响有待进一步深入研究。更多还原

【Abstract】 The interdecadal changes of both the East Asia summer monsoon（EASM） and the pressure system anomalies over China-Mongolia areas（30°⁵5°N, 70°¹20°E） as well as their relationship have been analysed, utilizing NCEP/NCAR reanalysed gridded data from 1958 to 2000, the result show that, in the lower and middle layers of troposphere, from the surface to 500 hPa or more, the negative correlation between EASM and the pressure system anomalies is quite clear. The coefficients are -0.67 （for sea level pressure） and -0.69 （for geopotential height on 500 hPa） respectively, which is significant at 99.9% confidence level. A clear change appears in the late of 1970′s. In the period of 1960₁976, both the surface and 500 hPa, the pressure system anomalies were negative centre over the China-Mongolia areas. It indicates that the areas dominate low pressure trough or cyclone activities. The strong southerly wind enhances the EASM and result in wet summer in North China. However, in the period of 1977₂000, in the China-Mongolia areas dominate the high pressure ridge or anticyclone activities, the stronger northerly wind over North China preveates the EASM flow form moving northward, and causes the weak EASM and the dry North China. Interestingly, on 100 hPa, mean geopotential height anomaly appears a dipole pattern: During the period of 1960₁976 it was higher in the east, lower in the west; vise versa during the period of 1977₂000. It would be needed further to study.更多还原