Climatic features of frontogenesis in East China and their related circulation patterns during the early summer

Based on the daily precipitation data of the 212 stations in East China and the NCEP/NCAR daily rcanalysis data in June and July from 2000 to 2010,the climatic characteristics of frontogenesis and their related circulations have been analyzed by employing the composite analysis. Our results have shown that the values of the frontogenetical function distribute non-uniformly in East China. The different terms in the kinematic frontogenesis function show the different intensity and distribution of frontogenesis in different places. The strongest frontogenesis as integrated from the different terms of the kinematical frontogenesis is observed in the Jianghuai area. Frontogenesis events arc classified as the 4 types as per the different shear types of horizontal wind along the strong frontogenesis belt at 850 hPa. They arc the warm type shear between southwesterly and southeasterly, the cold type shear between northeasterly and northwesterly (sub-type-Ⅰ),or between northeasterly and southwesterly (sub-type-Ⅱ),west wind type signed by the convergence between southwesterly and northwesterly, and the cast wind type by the convergence between the southeasterly and northeasterly. The different types of frontogenesis events occurred with different frequency in the past decade. In the Jianghuai area, the warm type shear frontogenesis happened mostly. 'hhc horizontal and vertical structures among different types of frontogenesis arc various apparently. It’s worth nothing that the 340 K contour of pseudo-equivalent potential temperature seems to be a meaningful indicator for the strong frontogenesis process since the 340 K contour parallels with the frontal zone and passes through it. The strong frontogenesis event seems to appear in a back-ground of the large-scale circulation pattern,which is quite different in different types of frontogenesis. For different types of frontogcncsis,the positions and intensities of the related cyclone and anticyclone along with the distributions of convergence and divergence,as well as the vertical structures of the circulation and so on arc found different to some extent. The close rclationships between the precipitation and the frontogenesis arc found. The stronger the frontogenesis is,the more precipitation is The daily precipitation related to the warm type shear is the strongest as compared to those related to other types of frontogenesis. The precipitation occurs usually in the frontal zone along the strong frontogenesis belt. The intensity of precipitation rclated to cold type shear follows the warm type, and both occurs south of the frontal zone with the rain belt tilted northeastward.The precipitation related to the west wind type comes thirdly in terms of rainfall intensity, occurring in the south side within the frontal zone.