| The cold-air snowfall is a unique phenomenon around Bohai, especially in Shandong Peninsula. However, it is still difficult to exactly forecast the areas, orders and duration of the cold-air snow in Shandong Peninsula currently. A typical process of cold-air snowstorm occurred in Shandong Peninsula during29th-30th December2010is selected to study with emphasis on its synoptic and microphysical and meso-micro-scale characteristics as well as effects of physical factors such as sea surface temperature and terrain, using the observed24h precipitation from synoptic stations,1h precipitation from automations, the NCEP-FNL reanalysis data and TBB data from FY-2D satellite, by the method of synoptic diagnostic analysis and numerical simulation. Firstly, the synoptic scale characteristics are analyzed. Secondly, six microphysical parameterization schemes of the meso-scale WRF model are used to simulate the process and high spatiotemporal resolution data from model output are imposed to analyze microphysical and meso-micro-scale characteristics in detail. Last but not the least, sensitivity tests are carried out by changing sea surface temperature and terrain height, in order to investigate their effects on cold-air snow and differences between them.Diagnostic analysis indicate that the upper environment is a feature of a cold-temperature and low-pressure center over Northeast China, with Shandong Peninsula in the back of trough, while the lower environment is a feature of intense cold advection. The TBB features show a meso-β low-convective systems and the low value is less than-30℃. It is not remarkable of the convergence upward motions in the large scale circulations. During the snowfall, high θse and PV(Potential Vorticity) maintain over Shandong Peninsula; moreover, the axis of high θse has a very good correspondence to the area of the snowstorm.The Lin scheme performs best and has simulated the primary characteristics and area of the snow band compared to other five schemes. Droplets are mainly under600hPa and their maximum maintain at900-800hPa, among which the content of snow and graupel are dominant. The evolution of droplets especially the graupel has a perfect relationship with snowfall period. This snowstorm occurs under the background of significant sea-air temperature differences, and large amount of sensible heat and latent and moisture are transported from the surface of Bohai to cold air, which are caused by turbulence. Vapor from the central region of Bohai Sea are transported to the northeast side of the Shandong Peninsula, and converge in a quite narrow region horizontally and relatively shallow vertically, only up to800hPa. It should be noted that the duration of the maximum of water vapor mixing ratio and the saturated layers of relative humidity are corresponding to the heavy snowfall period.The frontogenesis of meso-scale costal front which shows cyclonic shear between northerly and westerly winds in the horizontal wind fields. The local circumfluence of the costal front directly decides the area and intensity of the snowstorm, in addition, the updraft is the trigger of instable energy and the mechanism of shallow convective snow.Sensitivity tests indicate that the sea surface temperature (SST) around Shandong Peninsula has a remarkable impact on the area of heavy snow compared to the terrain. SST impacts on the amount of droplets and formation of low cloud by changing the upward sensible heat flux, latent heat flux and vapor flux, which results in the increase or decrease of cold-air snowfall. |
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