本文基于华北夏季降水资料和热带大气季节内振荡（Madden–Julian Oscillation，简称MJO）指数、NCEP/NCAR（美国国家环境预报中心/美国国家大气研究中心）再分析环流资料，采用多种统计方法分析MJO与2018年华北夏季降水的关系及影响机制。结果表明：（1）MJO与华北夏季降水有密切的联系。虽然MJO不能移到较高纬度直接影响华北夏季降水，但MJO对流区的气旋会在其北侧激发出反气旋环流，这对“气旋—反气旋对”在缓慢东移过程中，处于较高纬度的反气旋会直接影响华北夏季降水。即MJO会间接影响华北夏季降水，表现为当夏季MJO进入5、6位相时，华北地区夏季会出现明显降水过程，但降水强弱与MJO振幅大小有关。（2）影响机制方面。在850 hPa，伴随MJO的“气旋—反气旋对”的东移，它会造成华北夏季偏南风水汽输送加强（对应RMM1）或东南风水汽输送加强（对应RMM2），从而有利于降水过程发生。在500 hPa层，MJO通过中层扰动向中高纬的传播，诱导副热带高压移到朝鲜半岛附近并加强，对西来高空槽形成阻挡作用，有利于华北地区产生上升运动，从而有利于华北夏季降水过程发生。（3）可以用MJO制作华北夏季延伸期降水过程预报。
On the basis of the summer precipitation data from North China, the Madden–Julian Oscillation (MJO) index, and a reanalysis of the circulation data from the National Centers for Environmental Prediction/National Center for Atmospheric Research using statistical methods, this study analyzed the relationship between the MJO and summer precipitation in North China in 2018 and its influence mechanism. Results show the following: (1) The MJO is closely related to the summer precipitation in North China. Although the MJO cannot move to a higher latitude and directly affect the summer precipitation in North China, the cyclone in the MJO convective region will trigger an anticyclonic circulation to the north. During the slow eastward movement of the cyclone–anticyclone pair, the anticyclone at a higher latitude will directly affect the summer precipitation in North China; that is, the MJO will indirectly affect the summer precipitation in North China. When the MJO is in phases 5 and 6, there will be an obvious precipitation weather process in North China in summer. However, the precipitation intensity is related to the amplitude of the MJO. (2) In terms of the influence mechanism. At 850 hPa, along with the eastward movement of the MJO’s cyclone–anticyclone pair, the south wind water vapor transport (corresponding to RMM1) or the southeast wind water vapor transport (corresponding to RMM2) in summer in North China will be enhanced, which is beneficial to the precipitation weather process. At 500 hPa, the propagation of the MJO disturbance to the mid–high latitude will induce the subtropical high to move to the vicinity of the Korean Peninsula and strengthen it so that it will act as a barrier to the westerly trough and be favorable to the ascending motion in North China. Therefore, this is beneficial to the occurrence of summer weather precipitation in North China. (3) The MJO can be used to provide extended-range forecasts for summer precipitation in North China.
郝立生,LITim,马宁,梁苏洁,谢均. MJO对2018年华北夏季降水的影响.大气科学,2020,44(3):639~656 HAO Lisheng, LI Tim, MA Ning, LIANG Sujie, XIE Jun. Influence of MJO on Summer Precipitation in North China in 2018. Chinese Journal of Atmospheric Sciences (in Chinese),2020,44(3):639~656复制