Comparative analysis of two sandstorm processes caused by Mongolian cyclone

Two sandstorm processes caused by Mongolian cyclone were comparatively analyzed and diagnosed. The first process occurred during 19-22 March 2010 (case 1) and the second one during 28-30 April 2011 (case 2). The result showed that case 1 had wider range, stronger intensity and longer duration than case 2. Mongolian cyclones and upper cold vortex were main causes of these two cases. The cold front moved more southeastward and covered a larger area with stronger northerly wind in case 1. And the greater pressure gradient between cyclone center and high-pressure center was also contributed to the wider and stronger dust weather. Besides, secondary cold-front and supplemental cold air were propitious to the long-lasting dust weather. Vertical velocity was a good indication to sandstorms, and the upward motion area in case 1 was significantly larger than case 2. Helicity distribution demonstrated strong upward vortex motion which was helpful in sand rising at middle and lower troposphere, and the helicity in case 1 was more obvious. Cold advection and momentum downwash contributed to the intensification of surface pressure, cold high and pressure gradient, which leaded to stronger ground transformer wind and was favorable to the occurring of sandstorm. Case 1 had more obvious momentum downwash and transformer wind in the two cases. The decline of Ri along with increasing vertical wind shear and unstable stratification aroused and downstream transferred the sandstorm.