Statistic Analysis And Mechanism Study Of Snow-storm In Middle-and-high Latitude Region Of China

On the base of snowstorm precipitation data in 50 meteorological observatory stations during 20 winters from 1980 to 2000,we analyzed the temporal and spatial distribution of snowstorm in middle-and-high latitude region of China. Results showed that snow-storms mainly occurred at the early period of winter and the beginning period of spring; the area near Changbaishan Mountain in the east part of North-east of China, the north-west part and the area along Tianshan Mountain in Xinjiang are the largest occurrence number places.Through the analysis of 21 examples, we summed up three advantage types of atmospheric circulation features, and then we used a snowstorm example to compare the differences between Northeast and Xinjiang snowstorm. We also analyzed the elements of vorticity, divergence, specific humidity, moisture flux divergence, wind-field, wind shear, maximum lifting speed and so on in the snow-storm of North-east China, found that they are favorable for and benefited to the formation and development of snow-storm.We also analyzed the mechanic effects of blocking-high and coupling of upper and lower level jet in snowstorm, summed up different types of upper and lower level jet and their coupling course.By the analysis of the relationship among convective instability, symmetric instability and snowstorm, we found that the convective instability level is under 800hpa. Snow belt is located in the negative value region of moist potential vorticity and verified the theory of symmetric instability. The effect of horizontal component in moisture potential vorticity is larger than that of vertical component. That is a big difference between torrential rain in summer and snowstorm in winter. The instability in the middle and lower layer of troposphere is one of the triggers in snowstorm.