Contrastive Analysis on Frontal Structure of Quasi-Stationary Front in Two Precipitation Processes of Yunnan-Guizhou

The frontal structure features of quasi-stationary front in two precipitation processes of Yunnan and Guizhou and its formation and maintenance are analysed.The two precipitation processes are the cryogenic freezing rain and snow weather at the beginning of 2008 and low-temperature and rain weather at the beginning of the spring in 2009.There are both similar and different features.The similar features are: In the horizontal direction, 850 hPa temperature gradient are dense and the frontal zone are the compact district of isotherm.Behind the frontal zone,the low level inversion is very significant,the average inversion intensity is 2～8℃,its center lies between the eastern Guizhou and the western Hunan.In the vertical direction,the frontal zone are the compact district of the pseudoequivent potential temperature,it slopes northward and stretch upwards near 600 hPa.The frontal zone are the positive vorticity zone and the convergence zone of the horizontal wind on 850 hPa when the quasi-stationary front continus.The frontogenetical function that connected with quasi-stationary front both are positive.Yet the different feature are: the temperature difference of the surface layer is an important reason.In the vertical direction,the temperature field have not only cold-warm-cold characteristics but also one-level model characteristic in 2008,on the contrary,the temperature field has not the two characteristics in 2009.The low-level temperature field has cold center,which is above 0℃.The frontal structure are wide and gently slope northward in 2008,but it is narrow and sharp below 750 hPa in 2009.At the same time,there is an low subtropic frontal zone between 16°~17°N.The important difference causing frontal structure is that the horizontal convergence and denaturation of the frontogenetical function are difference to quasi-stationary front.