The Observation Analysis And Numerical Simulation Of The Large Area Ocean-effect Snowstorm In Shandong Peninsula

In winter ocean-effect snowstorms in Shandong Peninsula have distinct small and medium scale features, restricted to 1-2 observation stations. But since 1999 there have be four ocean-effect snowstorms in which heavy snowfall observation stations exceed four, which is called as large area ocean-effect snowstorms. In this study, those four snowstorms are comprehensively analyzed, mainly including temporal and spacial features, circulation features, and cold air activity. Afterward the ocean-effect snowstorm on 30 Decmber 2010 is intensively analyzed with Doppler radar data and simulative data of WRF model.The results show that large area ocean-effect snowstorms in Shandong Peninsula all occur in December, and heavy snowfall inYantai occurs from 00 LST to 08 LST,and in Weihai is from 08 LST to 14 LST. The heavy snowfall observation stations are all located in the north of the mountains. Yantai(including Muping) and Weihai(including Wendeng and Rongcheng) are the main distribution areas.When large area ocean-effect snowstorms occurr, the vortex on 500hPa is closed to Shandong Peninsula, ranging from 40°N to 48°N and from 120°E to 128°E. In contrast, the vortex on 500hPa is relatively far from Bohai and Shandong Peninsula in small area ocean-effect snowstorms.The strong echo zone extends from northwest to southeast in Yaitai and Weihai during heavy snow stage. The strong echo zone gradually moves to east in Yaitai, and keeps static in Weihai, and the location of the strong echo zone corresponds to the convergence zone of wind field. The strong echoes start to produce and weaken both on the Bohai Sea, and the echoes on the sea are always stronger than the land in the zonal direction in Yaitai, and because of topography the echoes are stronger on the land than the sea in the warp-wise direction. The altitude of the strong echos is under 700hPa in the whole snowfall.The movement of the horizontal shear line can cause the change of direction and location of the strong echo zone. The north shear line is relatively stable and the south shear line gradually moves to west in Yaitai, that causes the strong echo zone to rotate clockwise, and the south shear line is relatively stable and the north shear line gradually moves to west in Weihai, that causes the strong echo zone to rotate counterclockwise. The convergence of wind field extends from surface in Yaitai, and the higher the altitude of the convergence zone is, the higher the loction of the center of the strong echoes is, and the high starting altitude of the convergence zone in the east of Weihai influences ascending motion. The northeast wind cross Liaoning Province encounters the northwest or west wind in Shangdong Peninsula, forming the shear line, and the weaken west wind component affects the shear line to move.Bohai is the main moisture source of the snowfall and the moisture is transported to Shandong Peninsula by the northwest wind and converges in the north of Shandong Peninsula. High humid region is mostly under the layer of 850hPa,and the humid layer is shallow. Snow drop zones have a close relationship with the location of the ridge of high equivalent potential temperature,where the heavy snowfall is located.The strong upward vertical movement is in the lower troposphere,and the stronger upward vertical movement is,the heavier the snowfall is.