Numerical Simulation and Diagnosis Analysis of "3.12" Sandstorm in South Xinjiang

The frequency of sandstorm events is the highest in spring in Tarim Basin,China.A strong sandstorm happened in south Xinjiang on March 12,2011 was simulated by making use of the GRAPES mesoscale numerical model and the GFS data.Then a diagnosis analysis was done based on the output results of the model.It was proved that the GRAPES model can well simulate the occurrence,development and intensity of main weather systems including upper trough,westerly belt and surface temperature.They are main influence factors of the strong sandstorm.It can also well simulate the strong wind and ascending motion of strong sandstorm.The south invading and violent development of the cold West Siberian High is just the reason to cause strong sandstorm in the Tarim Basin.The horizontal distribution of potential vorticity has a certain indication for occurring time and area of the sandstorm.The helicity over the sandstorm area is negative value in the upper levels and positive value in the lower levels.There is a certain corresponding relation between the occurrence of sandstorm and the evolution of the positive value of the helicity over the sandstorm area.The time when ascending motion turned to declining motion was just the time of the strongest sandstorm happened.