干冷空气活动对2008年梅雨降水的作用

Activity of Dry Cold Air and Its Impacts on Meiyu During 2008 Meiyu Period

利用NCEP/NCAR再分析资料,分析了2008年梅汛期暴雨过程中干冷空气侵入对暴雨发生、发展和维持的作用。结果表明:梅雨期中高纬度环流的演变和调整与暴雨过程密切相关,亚洲北部阻塞高压(高压脊)的建立和维持,使得500hPa高度上西风锋区南压,导致干冷空气南下,极涡活动的异常偏东和加强有助于冷空气向江淮流域输送,有利于江淮流域暴雨的发展。在江淮流域梅雨期间,干冷空气的活跃与暴雨过程相对应。干冷空气来源于中高纬度和中高层。干冷空气侵入有利于对流层中高层干层的形成和维持。而且,干冷空气侵入是梅雨湿度锋形成和维持的一个重要动力和热力原因。在此研究基础上,归纳出中期预报着眼点,供实际业务预报参考使用。

By employing the NCEP/NCAR reanalysis data, the characteristics of the dry cold air activity, the dry cold air intrusion and evolution, as well as its impacts on the torrential rain during the 2008 Meiyu period are diagnosed.It is shown that there exists a close relationship between the evolution of the circulation over the mid-high latitudes and the torrential rain process, and the establishment and maintenance of the blocking anticyclone （pressure ridge） over Northern Asia lead to the southward movement of the westerly frontal zone and the dry cold air. The abnormal eastward movement and the enhancement of the polar cyclone transfer the dry cold air to the Changjiang River and the Huaihe River Basins, thus enhance the torrential rain over that area. It is also revealed that the northerly activities are in coherence with the torrential rain process, the dry cold air comes from the mid-high latitudes and the mid-high level. The Changjiang River and the Huaihe River Basins locate in the low level air convergence area. The north wind plays an important role in the enhancement of the convergence in the lower level and the divergence in the upper leve1.The dry cold air intrusion contributes to the formation and maintenance of the dry level. The dry cold air intrusion is one of the important dynamical and thermal causes for the formation and maintenance of moist front during the Meiyu period. At last, the keys of mid-range forecast are summarized on the basis of these results.