Diagnosis and Analysis of a Large-scale Sand-dust Storm Process Resulted from Mongolia Cyclone during Late April 2009

In this paper,using the meteorological satellite data,the dense observation and NCEP/NCAR re-analysis data,the cause of the large-scale sand-dust storm process over the north of China during late April 2009 was analyzed.The dynamic,thermodynamic and stratified unstable conditions of the process were diagnosed.Baikal blocking,high-level cold vortex and Mongolia cyclone were propitious for the dust-sand storm,and Mongolia cyclone was the key.Dry and warm tongue indicated the location of the area impacted by the dust-sand storm and the moving direction of the dust-sand storm.The development of upper jet flow was closely related to the dust storm.The storm weather mainly occurred in the right of inflow area of upper jet.With the jet moving southeastward and intensification,the sand-dust weather extended southeastward and enhanced.The helicity reflected the revolving and ascending in cyclone area during the process,and the high helicty area tilted backward.Richardson Number and vertical wind shear are important to sand-dust storm.It is easy to make for the occurring and transferring of sand-dust storm when Richardson Number declined and kept low value,vertical wind shear enlarged,and atmosphere was stratified unstable.