A Study Of The Mechanisms Of Shandong Central Mesoscale Terrain's Influence On The Convection Precipitation Process

It is one of concerned issues that the terrain's influence on the meso-scale convective activity and local rainfall in meteorology. In recent years, the meso-scale numerical models have made great progress, which give us a kind of available tool. Many people have used meso-scale numerical models to research the influence of terrian in south china and gotten many significative conclusion ,but the research of Shandong central terrain's influence is quite few. Shandong central mountain area lies in middle latitude of 35°N-37°N where all kinds of scales of synoptic systems are active. Moreover Shandong central mountain area is an isolated mountain area, where weather phenomenons are complex and various. So it has particular research value. This paper uses the Penn State-NCAR nonhydrostatic meteorological model(MM5) to simulate a typical case of heavy precipitation which happens in Shangdong central area in summer . Based on the reasonable results of the numerical simulation, two sensitivity terrain' influence experiments are designed and the results are used to analyze particularly Shandong central mesoscale terrain's influence on the mesoscale synoptic systems. The mechanisms of shandong central mesoscale terrain's influence on the meso-scale synoptic systems and local heavy precipitation are found partly.First, this paper uses the reanalysed ml data of NCEP to analyse the macrosacle circulation in the eastern Asia from 3rd to 4th, September 2003. The powerful subtropical anticycle controls Shandong peninsula in early time, while the lower atmosphere layer becomes warmer and wetter, which enhances the potential instability in Shandong peninsula. A small trough move to the northwest brim of the suptropical anticycle from Hetao, then move toward north along the brim of thesuptropical anticycle from 20LST 3rd to 08LST 4th at 500hPa. During this process, the upper atmosphere transfer kinetic energy to the lower atmosphere. This is one of measures which the heavy precipitation process get energy. After the "Dujuan" typhoon lands on Hainan island and Neizhou peninsula, a southeast low-level jet which comes to being between the northeast verge of typhoon and the southweast verge of the suptropical anticycle transfers moisure air toward the north china,which provides the affluent moisure air for this heavy precipitation process. The surface front entrys Shandong central area at 02LST 4th or so,which provides the favorable environment for the development of meso-scale synoptic systems.Then, this paper anaylses the heavy precipitation process and especially anaylses the development of the meso-scale synoptic systems by using the simulate result of MM5 and the data of GEOS9 satelliate infrared cloud. The paper shows that the cold atmosphere moves toward south along the east of the Taihang mountain and encounters the warm atmosphere in 925hPa, and a meso-scale P vortex comes into being because the atmosphere is disturbed by the tarrian of Taihang mountain in the south of Heibei province. One of the significant trait is the meso-scale P vortex is led toward northeast by upper air flow during this heavy precipitation process. The higher atmosphere layers transfer potential vorticity toward the lower atmosphere layers . The horizontal wind shear which is caused by the lower jet enhances the vortex too. Velocity difference between the lower jet and the vortex reaches 20m/s,which causes intense atmosphere convergence and vertical anabatic velocity in the southeast of the meso-scale β vortex. The anaflow make the instability energy release ,which causes the heavy precipitation process. Moreover, the paper finds that the isentropic surface of the meso-scale β vortex has the trait of that of typhoon.By using sensitivity experiments of terrain's influence, this paper finds that the warm and humid lower layers atmosphere which comes from the south of china is blocked by the tarrain of middle Shandong province and is forced to flow from the west of Taishan mountain and forms a lower level jet which moves toward the north of Taishan mountain. This lower level jet is important for the heavy precipitation.First, it makes the lower atmosphere layer become warmer and wetter, which enhances the potential instability in the west of Shandong central area; Second, because it makes the warm and humid atmosphere accumulate in the lower layers, the isentropic surfaces becomes steeper, which is favorable for the form and development of meso-scale vortex; Moreover, it enhances the gradient of —X componment of 9 se and the vertical shear of V in the west and north of Shandong central area, which increases the baroclinicity of moist potential vorticity. This paper finds Shandong central terrain can reduce the precipitation in the north it and enhance theprecipitation in the area between the southwest of Shandong central area and the south of Taishan too. This paper compares the differences of some meteorological physical variations between control experiment and sensitivity experiments of terrain's influence at Taishan, Taian, Ninyang stations . The terrain of Shandong central area enhances the water vapor convergence, vertical velocity and atmosphere convergence at three stations during the heavy precipitation process. The increment of precipitate reaches 50% or so.