| The hail damage is a meteorological disaster caused by the strong convective weather systems, which has characteristics of obvious seasonal and paroxysmal. A large range of severe hailstorm often accompanied by paroxysmal extreme disastrous weathers process, such as strong winds, heavy rain, plunged temperature and so on. Hail is one of the most important extreme weather in Jiangsu Province. Although it occurs within narrow zones and shorter in duration, it is fast, violent, intensity and often along with strong winds, heavy rain.which cause serious damage to human-made structures and, most commonly, farmers’ crops. Therefore, this becomes particularly important for us to do analysis of hail temporal and spatial variation, weather background and the main climatic characteristics in Jiangsu Province. This paper used WRF model to simulate a number of hail, combined with information provided by Doppler weather Radar, to reveal the causes of hail and the impact of the underlying surface to hail, and through statistical analysis of simulation output of hail cases, to find early warning parameters and forecast indicators of the hail, in order to improve the forecast accuracy of hail, as well as provide a scientific basis for government to guide disaster prevention and reductionBased on the observed hail data of70meteorological stations in Jiangsu province during1980to2009, in this study, the temporal and spatial distribution characteristics of hails were analyzed. Mann-Kendall method, a tool of detecting the extraordinary climate variations, was used to discuss the influence of the climate warming on the occurrence tendency of hail disasters in Jiangsu. The results were showed as follows:(1) the inter-decades variations of hail disasters in the whole province were that the highest frequency period of hailing occurred in1980s of the last century, the hailing days per year in1990s reduced obviously, but it had a remarkable raising tendency since2000.(2) The main occurring seasons of hail in Jiangsu Province were spring and summer and their hailing days accounted for94.7per cent of the total hailing days in a year. The concentrated hailing months in a year was April, May, June, July and August. Among them, the month of maximum hailing days was June and the second frequency month was May in the coast regions and the northern side of the Huai River Valley of the province, but the maximum frequency month of hailing was May, the next was June in the other regions. December, January and February in winter has been the rare hailing months of a year.(3)The spatial pattern of hailing in the province was that the hailing days in the eastern coast regions of the province is more than the western inland regions, the hailing days in the middle and north part was more than the south part, Xinhua City in the Lixia River Region and Sheyang along the coast of the Yellow Sea were the high frequency areas of hailing days in the whole province and the Nanjing-Zhengjiang Hilly Region was the lowest frequency area of hails.(4)In recent30years, the hail has four main routes in the province.(5)The spatial variance coefficient of hailing days increased progressively from the northeastern part to the southwestern part in the province.(6) The main mechanisms resulted into this spatio-temporal change situation of hails in the province were the global climate warming, the backgrounds of atmospheric circulation, the local atmospheric dynamic fields, the landforms undulation and the thermodynamics attributes of the surface.Based on mesoscale numerical prediction models WRFV3.1, using the NCEP1°×1°reanalysis data, the routine meteorological observation data and Doppler Radar data, the hail occurred in June5,2009in the Jiangsu was simulated. By diagnostic analysis of the physical quantities of the model output, found that:(1) the strong convective weather produced in the weather ground which northeast cold vortex is a steady move, weak cold air south after vortex and the ground is warmer and humidifier before the cold front;(2) The CR is above55dBz, appears the positive and negative speed or the cyclone, VIL is more than55kg·m-2, and the echo top is above9km, etc in Doppler Radar. These verified the generation process of hail. There are important guiding significance in potential forecasting for the severe convective weather.(3) In the eastern coastal of Jiangsu Province a steady stream of water vapor transport and moisture convergence from convergence zone in low-level, provided moisture conditions for the formation of hail. While hail district exists the under wet on dry stratification conditions.It has dry area near700hpa, dry and warm air in the lower promotes the development of the strong storm.(4) Before the hail, in eastern of Jiangsu Province, It has a greater than1600J·kg-1high-energy band, corresponding to radar echo zone. The surface convergence systems as dew point front, the sea breeze front and strongly vertical upward motion provide adequate thermal conditions and dynamic conditions for the development of the hail.(5)0℃layer height is3.5-4km,-20℃layer height is5.5-6.0km, which are suitable for hail growth. Thickness between0℃and-20℃C layers is180to220hPa, the thickness ratio of warm clouds and cold clouds is1:2to1:5are also suitable conditions for hail growth.Considering the underlying surface factors, this paper used WRF Model simulate the process of hail on June5th,2009and carried out a series of sensitivity tests, the results showed that:the different underlying surface and terrain caused non-uniform heat. It through affected low-level wind, temperature, wet weather factors to influence the hail and other severe convective weather. Water body can cooling local temperature, while increased the humidity over the water body, block to the wind.Hills and plains, coastal differently effect temperature, humidity etc. Otherwise it also enhanced or reduced local circulation... |
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