Abstract: By using the data from 25 observation stations in Ningxia,the sounding data from Yinchuan observatory and the ECMWF ERA-Interim 6-hourly reanalysis data with resolution 0.125º×0.125º,the weather situation, the influence system,the thermal,the dynamic conditions and the formation mechanism of the strong wind and weak dust process on May 11,2016 are analyzed. The results show that the strong wind and dust present a time phase inconsistency characteristics,the dust reaches its strongest stage ahead the wind 6 hours and tends to die out at the strongest stage of the wind. The 200 hPa high-level jet flow,500 hPa frontal zone,700 hPa low-level jet flow and the ground cold front is the main influencing system. Strong wind in different stages plays different roles in dust,conducive to the transmission of the sand in the early stage and restrains the development of the sand in the later stage. Further analysis shows that the high momentum carried by the 200 hPa high-level jet flow passes down through 500 hPa frontal zone,which is momentum down,and contributes to the formation of 700 hPa jet flow. The important mechanism of momentum transfer is the downward transmission of high level high vortex in the troposphere,potential vorticity region (≥2.0 PVU)down to 520 hPa with the strongest wind. At the same time,the downward momentum transmission is accompanied by the downward transmission of the cold advection in the upper air,which leads to the increase of the ground air pressure and the formation of the isallobar wind. Cold advection that is transmitted to the lower layer and surface sensible heat flux makes the atmospheric stratification unstable,through strengthening the ground turbulence to form a hybrid layer,which makes the high momentum of the 700 hPa jet flow spread to the ground and increase the surface wind speed and the maintenance and development of the dust. It can be seen that the momentum transportation downward and isallobar wind are the direct mechanisms for the formation and the development of strong winds,and the sensible heat flux is the indirect mechanism. The occurrence and development of dust is due to thermal unstable stratification,which is caused by the cold advection and the surface sensible heat. Isallobar wind and the wind formed by downward momentum are the transport mechanism of the dust. Furthermore,the inhibition effect of cold advection center (750 hPa)and the absence of secondary circulation lead to the weakness of the dust. Atmospheric stratification tends to bring the end of the dust,and the downward momentum transportation is the direct cause of the demise of the windy weather.

Key words: blowing sand, momentum transportation downward, sensible heat flux, cold advection, isallobar wind, unstable stratification