Analysis Of The Formation Mechanism Of Severe Convective Weather In Shandong Province In Summer

Through using the NCEP1°x1°reanalysis datas, conventional surface observationsand upper-air sounding datas， this paper discusses the temporal and spatialdistribution characteristics, the water vapor and vertical movement characteristics,physical field and the unstable situation index parameters of the severe convectivethunderstorms which occur in Shandong Province from2005to2009in the summer.The results show that: the thunderstorms in Shandong Province has strong seasonaland regional characteristic. The the time distribution characteristics of severeconvective weather in Shandong Province is that thunderstorms mainly occur in June,July and August; the spatial distribution characteristic is that in the western region andthe peninsula region of Shandong the number of the days when thunderstorms occuris small, and in the northern part, central part and the southern part of ShandongProvince, the number is large. The areas where thunderstorms occur more generallyshow north-south zonal distribution. The major weather systems which affecting thesevere convective weather of Shandong Province are these: trough, cold vortex, theedge of the subtropical high and northerly airstream. Among them, the trough, coldvortex and the edge of the subtropical high cccupy most, the percentages are morethan95%.It is founded that by the reseach, there are80times of thunderstorms which havethe obvious downward motion before the thunderstorms occur in the84times ofthunderstorms from June to September of the Shandong region in2005-2009,accounting for95.2%of the total. It’s about12-36hours before thunderstormsoccurred, sinking movement more occur in the high layer of the troposphere. Thissinking motion is mainly due to the effect of dry and cold air in the middle and upperlayer of the troposphere about from200hPa to700hPa or the upper air current beforethe thunderstorms occur. By the influnce of dry and cold air flow or the upper aircurrent, the strong sinking motion began to appear from the upper layers. If there arestrong warm air delivered to the Shandong region, it will be more easy to trigger therelease of the disturbance energy of the unstable convective weather, resulting in theoccurrence of the thunderstorms. This wide range of sinking movement is animportant symptom of the thunderstorms before they occur in Shandong in summerand it can be used as a pre-signal of Shandong before thunderstorms occur in summer,by combining with outputs of the numerical weather prediction modelThe analysis of the cases also shows that by contrasting the sinking motion area andthunderstorms occurred area, it can be seen that areas of sinking motion will generallyhave the occurrence of thunderstorms whether in a general trend or in the small-scale.The area where thunderstorms occur not only need the sinking motion，but also need that the stratification instability must reach the standards. The analysis also show thatthe global reanalysis data can be used to forecast convective weather. The higherresolution of the global reanalysis data also can make the resolution of the forecastingof severe convective weather higher in space and time.When the thunderstorms occur in Shandong Province, the ω of300hPa is generallyless than-0.76Pa·s-1. It can be considered as a very valuable reference index ofthunderstorm forecasting of Shandong Province in summer. The K index is mainlyconcentrated in this interval:28.5-31.0. The TT index is mainly concentrated in thisinterval:45.0-55.0. LI lifted index generally appears at-5--7. The three indexs whichexpress unstable provide important references for the forecasting of severe convectiveweather of Shandong Province in summer.