Study On The Key Technology For Forecasting Severe Convective Weather In The Northwest Of Shandong

Dezhou City locates at 36°24′-38°0′N,115°45'-117°24′E, the north shore of the lower Yellow River, lying in north-west Shandong Province. The region is covered by plains with altitude 20 meters or so, about 200km apart from Taihang Mountains in the west. There is a high incidence of severe convective weather in northwest Shandong, which is second only to the central mountainous areas in Shandong Province. Severe convective weather happens frequently almost every year to bring hail and high winds disasters causing serious damage in the area. In the thesis we first analyze the temporal and spatial distribution characters of climate of severe convective weather in northwest Shandong, with compared to other regions in the province. The distribution of severe convective weather has an obvious seasonal and territorial characteristics in the northwest Shandong, which is one of the most prone areas of severe convection in the province, basically same as the province, but different in the monthly distribution of severe convection from other regions.Based on the 71 severe convective weather cases in Dezhou City from 1979 to 2006, using JMA JRA25 1.25°×1.25°reanalysis data on GMT 00,06,12,18, we classify the severe convective weather background according to the synoptic system leading to severe convection and get four categories:low vortex, upper-level trough, transverse trough, northwest flow, low vortex type hail accounted for 56.3% of the total, upper-level trough 16.9%, northwest flow 15.5%, transverse trough 11.3%. Synthesized analysis for each type of severe convective weather by selecting the samples is put up to summarize the background of the typical characteristics of different weather model, with the configuration between middle-level and low-level being discussed. According to the physical generating mechanism of severe convection, the diagnostic analysis of a variety of strong convection parameters are carried out, thermal convection parameter K index, uplift index LI, showalter index SI, the total temperature index TT, CAPE, dynamic parameters 0～1km,0～3km,0～6km wind shear SHR, the storm relative helicity SRH, dynamic and thermal composite index severe weather threat index SWEAT, storm intensity index SSI, energy helicity EHI, as well as the 0℃layer height ZHT and -20℃layer height ZHT20, these variety of physical parameters of convection is useful to determine instability of the atmosphere and the possibility of hail in the northwest Shandong, with some parameters having a certain difference threshold used in other parts at home and abroad.In this paper, aiming at the severe convective weather on July 5,2006, we had analyzed the weather background, detailed physical actors and diagnostic analysis of physical quantity. The results show that:the impact of cold vortex, high-level cold air intrusion, which may trigger instability in the energy release, is caused the main reason for the severe convective weather. By the stability and environmental wind field analysis it shows that when the severe convection occurs 12 hours before, there is the east wind under the 850hPa level, which plays a important role in transporting water vapor from the west of the Bohai Bay, resulting in increasing the humidity and tending to saturate the atmosphere in this area. The characteristics of the atmosphere stratification which structure is moist in low-level with dry in the upper-level are consistent with the conditions where hails happen often. By calculating lots of parameters of severe convection it shows that the air over this area is unstable, which can indicate well where the convective weather occurs. The high-value center of dynamic parameters 0-3 km SHR and SRH is magnificently consistent with the place where the hail and gale break out, which indicates that wind vertical shear is the key factor to determine the organizational structure and strength of thunderstorms. The analysis of Fy-2c Satellite infrared cloud-images indicates that the TBB of cloud cover reaches at-40℃to-55℃when the severe convection is occurring in northwest Shandong, while the most intense hail and gale weather mainly occur in which there is the largest brightness temperature gradient region in front of thunderstorm cloud. The analysis of CINRAD Doppler radar data shows that the severe convection in the northwestern Shandong is mainly causing by the super-cell and multi-cell storm on the "bow" echo whose center intensity are above 55dbz, the maximum reaching 65dbz. The super cell storm at the top of bow echo causes the most severe weather, with mesocyclone existence in the lower-level and the radial velocity positively correlated with the surface wind speed; VIL is above 50 kgm-2 in the zone where hail occurs, indicating that VIL products is very good correlated with hail, while its value can be a good indication to the existence of hail.