Based on case study and climate analysis , this work arrives at the central cause of dv of the meiyu rainfall , which lies in the regional difference in dv of the lower - level temperature field of east asia , and the cause relates essentially to 1 ) distinct topography in this region and 2 ) a particular cloud pattern during the wet season 本文通过实例分析、气候比较和数值模拟认为：梅雨降水日变化的根本原因是东亚低层大气温度场日变化的区域性差异，造成这种差异的基本原因又包括两个方面，一是东亚特殊的地形构造，二是梅雨期内特殊的云区分布。
Based on the ncep / ncar reanalysis products , the sea ice concentration data and the observation rainfall data in china , the seasonal , intraseasonal and interannual variations of the atmospheric circulation in the southern hemisphere ( sh ) are systematically analyzed together with their influences on east asian summer monsoon ( easm ) . the major conclusions are summarized as follows : ( 1 ) in the lower level of the troposphere , the semi - annual oscillation ( sao ) is most active along 40 s and 65 s in the extratropics of the sh . over these latitudes , the variance percentages of sao exceed 70 % , and the anti - phase variation of the sea level pressure ( slp ) between the two latitudes is primarily caused by their sao components 利用ncep ncar再分析资料、南半球海冰密度资料及中国台站降水资料，本文系统分析了南半球大气环流的季节、季节内和年际变化特征及其对东亚夏季风的影响，主要结论归纳如下： ( 1 )对南半球热带外大气环流而言， 40 s和65 s是低层大气准半年振荡最为显著的两个纬带，在这两个纬带上，半年波的贡献都超过了70 ，二者季节变化的反位相主要体现为半年波分量的反位相。
Regional difference in lower - level temperature dv and pressure dv are greatly weakened and dv of llj is distinctly faint without the nanling ridge . this result show that nanling ridge acts as a critical role in the establishment of dv of the lower - level temperature and pressure , which give rise to the dv of llj in south china 而当模式中仅仅去掉南岭和武夷山山脉地形后，低层大气温度场日变化的区域性差异明显变弱，梅雨低压带南侧原南岭山脉所在地的温度日较差明显减小，使得梅雨低压槽与华南地区之间的南北向水平温度梯度和水平气压梯度的日较差显著变小，导致华南低空急流日变化的显著减弱。
