Upper-air climate background analysis of convective weather in Beijing

Climate background analysis of convective weather was the foundation of nowcasting,which was the necessary to Olympics weather service in 2008.Thus,air pressure,temperature,humidity and wind speed from upper-air sounding intraday 0800(BST) data(2002-2005) under convective weather of warm season(May to September) including thunderstorm,hail,rainstorm and high wind were analyzed,and they were compared with climate average values,in order to reveal the environmental conditions and rules caused the convection and to serve for forecast operation.The results indicated that relative monthly upper-air elements of convective weather were of typical characteristics.There was a corresponding relationship between 500 hPa jet and convection.Convective weather occurred easily while jet existed,and the joint probabilities of thunderstorm,high wind,rainstorm and hail increased.There was a better corresponding relationship between convective and vertical shear of wind direction.The average probability of wind direction that veered clockwise under 500 hPa in convective weather was 84.2%.Mixed convective weathers often occurred when wind directions veered counterclockwise.The higher the counterclockwise rotation height was,the stronger the convection was.Rainstorm occurred easily in many stations if the entire wind directions veered clockwise,but the thunderstorms occurred uneasily.