Analysis on the formation mechanism of a strong squall line based on intensive observation data in Shangqiu on June 3, 2009

Based on intensive observation data from the new generation weather radar in Zhengzhou, Shangqiu and the data by the minutes from automatic station in Henan, the formation mechanism of strong squall line in Shangqiu on June 3, 2009 was analyzed. The results show as follows. The cold air carried by transverse trough in the rear of low vortex down along the northwest airflow joins low-level warm moist air in Shangqiu and is triggered by both the low-level convergence line and dry line, a strong squall line broke out in Shangqiu where is in the convergence center. The initial convective echoes developed and strengthened along the boundary convergence line and formed a severe supercell storm. Under the action of dew point front (dry line) between Kaifeng and Shangqiu, a newborn convection triggered by the developed clear air boundary convergence line developed, strengthened and joined the severe supercell storm to form the strong squall line moving rapidly southeastwards to impact Shangqiu area. Before thunderstorm wind happened, a lot of super-refracted echo in Shangqiu indicated an existing dry and warm lid which provided a great deal of instable energy for outbreak of more severe convective weather after the squall lines moved to Shangqiu. The supercell storm reflected in the strong squall line echo band and later evolved bow echo were the key factors causing the strong squall line in Shangqiu area. The thunderstorm winds occurred in the back of the convergence line which had the typical characteristics of mesoscall thunderstorm high, mesoscall low-temperature center, wind field convergences and so on. The severe thunderstorm high,strong pressure gradient in front of high and strong squall line moving fast resulted in the extreme high wind since meteorological records in Ningling, Xiayi, Yongcheng and other places.