Analysis on Black Storm Cause in Hexi Corridor on 24 April 2010

Using the conventional sounding and ground enhanced observation data,based on dynamical diagnosis and mesoscale method,the causes of a regional strong sandstorm in Hexi corridor on 24 April 2010 is analyzed.The result shows that the main reason of strong sandstorm formation is the surface heat low with cold front.The large-scale system of forming strong sandstorm is that the polar cold air ahead of Ural Mountains high pressure ridge erupts toward south.The strong barocliny on 700 hPa over Hexi corridor,Gansu Province is not only advantage to frontogenesis and low level convergence,but also momentum transport along downward.The large gradients of pressure and temperature before and after cold fronts are caused by development of thermal low pressure,which provide the thermal instability condition for convection development.Ascending motion before cold front and overlap of upper and lower jets provide the developing condition of deep vertical circulation for information of black storm.Using the sounding data before and after black storm ocurring,the atmospheric dynamic characteristic as 'windstorm horizontal helicity' and thermal characteristic as 'V-3θ' are calculated and analyzed.The result reveals that reasonable atmospheric temperature-humidity structure is beneficial to forming and developing of sandstorm.