Observation and analysis of“07.3”severe sandstorm

The sandstorm that occurred on 27-28 March,2007 in the northwest of China was analyzed with observed data from the Minqin station and the Semi-Arid Climate and Environment Observatory of Lanzhou University(SACOL),and also with weather reports,objectively analyzed data and satellite images.The main results are:Synoptic analyses of the sandstorm indicate that a quick development of the short wave trough at 700 hPa and 850 hPa associated with surface cold front contributed to the formation and development of the sandstorm.Observed data at the Minqin station show that the mass concentration of PM_(10),pressure and wind speed at ground levels underwent obvious variation during the sandstorm's development.The pressure and wind speed had a jump when the sandstorm broke out and the variation of pressure was ahead of the wind speed, which means that the adjustment between the wind field and pressure field was obvious when the sandstorm broke out.The vertical shear of wind speed and concentration of PM_(10) reached their peaks simultaneously. However,the peak of the vertical shear of temperature was ahead of the peak of mass concentration of PM_(10) and wind speed.The strong wind speed favored the emission of dust and,at the same time,the strong vertical shear of wind speed favored the release of instable energy and the formation of the sandstorm.Observed data at SACOL show that the mass concentration of PM_(10),pressure and wind speed at ground levels underwent obvious variation during the development of the sandstorm.Wind speed and pressure at SACOL reached their peaks ahead of the mass concentration of PM_(10).The vertical shear of temperature reached its peak ahead of the mass concentration of PM_(10) and lagged behind the vertical shear of wind speed.