Analysis Of The Differences And The Causes Between The Two Squall Line Process In June2009

In this paper, we study the environmental background, the difference of structure feature and the reason for the different weather phenomena of two strong squall line which occurs in Jianghuai region on2009June3to6by using the conventional observation data which includes ground and radiosonde, radar reflectivity data, and FNL1degree*1degree analysis data that provides from NCEP centre and combining with the mesoscale numerical model(WRF) simulation results.The result shows that, although two squall line process is similar in some aspects: circulation form in500hPa,strong unstable energy accumulation and uplifting mechanism, vapor is quite different in low layer(900tol000hPa),especially form700hPa to800hPa is more significant difference. The average relative humidity of0603process is just about40%,but0605process is about90%form700hPa to800hPa.In addition, the0603squall line process is mainly to westerly vertical wind shear, the0605process is mainly to northerly vertical wind shear. The following500hPa mainstream direction leads to the two squall line’s effect path different.Numerical simulation shows that, the two dynamic structures of squall line are similar, the low level which has upwardly and rearwardly flow in front the squall line with the backward squall line’s forward flow are convergence in the convection zone before the squall line occurred, lead to consistency strong and narrow updrafts. The mature stage of the squall line convection zone is updraft in high,and divided two after arriving to high. Low level corresponds to the downdraft,and the downdraft forms divergent flow when it reachs to the ground, together with inflow in the squall line front joined to form a gust front. The same thermal structure of the two squall line process is updrafts accompanied with high-energy and warm air in front, the middle level’s inflow is accompanied by low energy and cold air. Their difference is the distribution of the vertical pseudo-equivalent temperature, before the0603squall line process under the700hPa is neutral stratification, from700hPa to500hPa is unstable stratification, above500hPa is stable stratification. But the0605squall line process has a shallow stable stratification below900hPa,above900hPa changes to unstable stratification, there is a turning point near900hPa,this situation is advantageous for the formation of hail.The trigger mechanism of two squall lines is different. The0603process is triggered by the middle level gravity waves, before the convection occurring, gravity wave generates in middle level, with the gravity wave moves to eastward and southward, there generates warm convective bubble in front, and the development of the convective bubble destroy the stable stratification,’broken’ the gravity waves, leading to the further development of the convection system. The trigger mechanism of0605process is mainly the sea breeze front, before the convective, due to differences in land-sea thermal leading to sea breeze front, the sea breeze front which is gradually increased is inland invasion, and the air is forced to rise, triggering strong convection generated.The clouds microphysical structure and water vapor test of two squall line process results showed that cloud water mixing ratio, graupel water mixing ratio and rain water mixing ratio are mutual constraint relationship, when convection occurs, cloud water mixing ratio first appeared, its quantity effects graupel water mixing ratio, then effects rain water mixing ratio. Water vapor test result shows, the amount of water vapor between700hPa to850hPa is very sensitive to graupel(hail) water mixing ratio, the water vapor increases in this region, then the graupel(hail) water mixing ratio increased significantly, on the contrary, significantly reduce.