Climatic Features Of Frontogenesis And Their Related Circulation Patterns In East China During Meiyu Period In The Past Decade

Based on the daily precipitation data of212stations in East China and NCEP/NCAR daily reanalyses in June and July from2000to2010, the climatic characteristics of frontogenesis and their related circulations have been analyzed by employing the composite analysis in the present paper. Our results have shown that:(1) Frontogenesis occur with high frequency in East China. The frequency values of frontogenesis are fond in different place and for different types of frontogenesis. In conjunction parts of Zhejiang, Anhui and Jiangxi provinces, highly frequency occurrences of total frontogenesis are observed. They occur49times per year on average. Between high frequency and low frequency frontogenesis years, it is found significant different scenarios in the abnormal pseudo-equivalent potential temperature, wind, humidity, geopotential height and so on. These differences are responsible for explaining why the higher frequency occurrences of frontogenesis are observed in these years where as lower frequency occurrences of frontogenesis in other years.(2) The values of frontogenetical function distribute non-uniformly in East China. The value of different term of the kinematic frontogenesis shows different intensity and distribution of the corresponding frontogenesis in different places. The strongest frontogenesis as integrated from different terms of kinematic frontogenesis is observed in Jianghuai area. Frontogenesis events are separated into4types as per the different shear type of horizontal wind along the strong frontogenesis belt at850hPa. They are 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 east wind type by convergence between the southeasterly and northeasterly. The different types of frontogenesis events occurred with different frequency in the past decade. In Jianghuai area, the warm type shear frontogenesis happened mostly. The horizontal and vertical structures among different types of frontogenesis are various apparently. It’s worth nothing that the340K contour of pseudo-equivalent potential temperature seems to be a meaningful indicator for the strong frontogenesis process. The340K contour parallels with the frontal zone and passes through it. The strong frontogenesis event seems to appear in a background of the large-scale circulation pattern, which is quite different in different types of frontogenesis. For different types of frontogenesis, the position and intensity of related cyclone and anticyclone along with the distributions of convergence and divergence, and the vertical structures of the circulation and so on are found different to some extent. The close relationships between precipitation and frontogenesis are found; where the stronger the frontogenesis is, where more precipitation is received. 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 related to cold type shear follows warm, which occurs all south of the frontal zone, and the rainbelt tilts northeastward. The precipitation related to the west wind type comes third in terms of rainfall intensity, occurring in the south side within the frontal zone. Affected by the typhoon, the precipitation of east wind type is received mostly over sea other than land in these cases.(3) The tilt frontogenesis occur frequently in the East China and the surrounding areas. There are four frontogenesis function maximum centers, Located in the provinces junction of Zhejiang, Anhui and Jiangxi; Hunan and Hubei; Guangxi and Taiwan. The strongest frontogenesis occur in the three provinces junction. Frontogenesis events are separated into5ypes as per the different shear type of horizontal wind along the strong frontogenesis belt at850hPa. They are the cold type shear between between northeasterly and southwesterly,the warm type shear between southwesterly and southeasterly, west wind type signed by the convergence between southwesterly and northwesterly, the east wind type by the easterly and the warm zone type. For different types of frontogenesis, the horizontal structure and the vertical structures of the circulation are found different to some extent. In the first four types, the vertical structure of the tilt frontogenesis is similar to the equatorial front. The front zone boundary tilt to the south with height. The tilt frontogenesis of the warm area type does not play a major role to the warm frontal genesis in general frontogenesis, so its vertical structures is similar to the general frontogenesis of the warm type shear. The close relationships between precipitation and the tilt frontogenesis are found. The daily precipitation related to the cold type shear and warm zone type is the strongest as compared to those related to other types of frontogenesis. The former precipitation occurs usually in the frontal zone along the strong frontogenesis belt. The precipitation from the warm area type occurs in Jianghuai area in the north of the key area. The intensity of precipitation related to the warm type shear and west wind type follows cold, which occurs all south of the frontal zone. The precipitation of east wind type is least...