Abstract:  

Two heavy blizzards in northern Xinjiang, China happened on February 23,2014 and March 2,2016.Although the central location and snowfall size of the two blizzards were similar, the hourly snowfall and snowfall duration of the two snowstorms were different. In particular, during the heavy snowfall in March 2016,the maximum hourly snowfall at some observation stations were nearly 4.0 mm, reaching the historical maximum since the setup of the recording system. But the maximum hourly snowfall of the blizzard in February 2014 was only 1.8 mm at the observatory. In order to understand the difference between the two blizzard weather events, this paper investigated the weather process about the two events using the meteorological observational data, NCEP/NCAR 1°×1° re-analysis data, the GDAS (Global Data Assimilation System) data and the HYSPLIT4.9 model, FY-2E data and Doppler radar product. The results are summarized as following: The snowfall areas of the two blizzards were both located in the overlaying area in front of the 500 hPa trough with shearing or converging at the low-levels, diverging at the high-level, and large temperature advection gradient in the vertical direction, and in the larger gradient of the edge of the cloud TBB center. Domestic researchers has studied more about the effects of frontal forcing and symmetric instability on heavy rain, but their application in blizzard was less involved. Diagnosing atmospheric stability through moist potential vorticity revealed that the location of the blizzard center in 2016 and the area with moist potential vorticity negative value were basically the same. There was a moist symmetric instability over the blizzard area which is similar to that of a rainstorm. This mechanism can help the inclined updraft be formed and developed, then cause the release of a large potential unstable energy in the atmosphere and provide unstable mechanism for blizzard. When moist symmetric instability was gone, the hourly snowfall was also decreased. Therefore, this moist symmetric instability structure was the main cause of the large amount of snowfall in the blizzard in 2016.However, no moist symmetric instability was found in the blizzard in 2014, indicating that the conditional symmetric instability was not the only cause in northern Xinjiang. It may be affected by other mechanisms of instability, dynamic factors and thermal factors, but it had a significant effect on the increase of snowfall intensity per unit time. Snowfall was closely related to low-level jet. The intensity, duration and scope of the echo center were consistent with the changes in the center of the strong snowfall.

Key words: northern of Tianshan Mountains')">northern of Tianshan Mountains, blizzard, most potential vorticity, diagnostic analysis