Research On Snowstorm In Heilongjiang Province

By using the stational snowfall dataset from Meteorological Information Center of Heilongjiang Meteorological Administration,the NCEP/NCAR daily reanalysis data, and the daily observation dataset of the northern hemisphere from National Meteorological Information Center of China Meteorological Administration, as well as T639L60 model data, the climatic distribution of snowstorm are analysed in Heilongjiang province, and the synoptic situations are classified. The main features of synoptic situations are found with the typical case. The planetary-scale system, the synoptic scale system and the physical feature are discussed through a lot of case studies.The characteristic of doppler radar and cloud image of snowstorm are given and the conceptual models of background field of all kinds of synoptic situations are summarized in Heilongjiang province. The major conclusions are as follows:(1) The climatic distribution of snowstorm in Heilongjiang province is closely related to the terrain. The snowstorm centre is situated in the Da Hinggan Mountains, zhangguangcai Mountains and laoye Mountains. Trumpet-shaped topography prominently increased snowfall between Da Hinggan Mountains and wanda Mountains.The latest snowstorm occur in mid April in spring and the earliest snowstorm occur in mid October in autumn.It is found that the largest snowstorm precipitation is in spring and autumn of the transitional seasons. The snowstorms are caused by the confluence of southeward warm and moist airflow and the fluctuation in the westerlies. The interannual variability of snowstorm is very obvious while the climatic linear trends of snowstorm are inapparent.(2) There are four kinds of synoptic situations of snowstorm for Heilongjiang province:the Baikal Lake vortex pattern, the Mongolia cyclone pattern, the Japan low pressure pattern, the Jiang-Huai cyclone moving northward pattern. The conceptual models of frontogenesis are given for Heilongjiang province,and the methods of judging frontogenesis are summarized.The prediction index of snow are given that snow or rain depends on 850hPa temperature,850 hPa temperature advection and altitude.(3) There are seven patterns of temperature and pressure of snowstorm for Heilongjiang province:the north ridge and south trough pattern, the north shallow and south deep of low trough pattern, the contour lines parallel to isotherms in front of low trough pattern, the vortex initiation pattern, the eastward inverted warm advection in the north of vortex pattern, the occlusion front in front of vortex pattern and the northwest wind pattern.There are three patterns of streamline at 500 hPa of snowstorm for Heilongjiang province:the 0 pattern,the double vortex pattern and the dipole pattern.(4) The synoptic-scale systems for Heilongjiang snowstorm are the trough, the vortex, the high-level jet, the low-level jet and the cyclone. The synoptic-scale systems cause the mesoscale systems initiate, convergence the water vapor, cause the geopotential instability and the vertical wind shear is favorable for meso-scale systems initiate and maintaining.(5) The mesoscale systems cause the snowstorm process directly and the shear line, the convergence line, the significant streamline, the moisture tongue are the characteristic lines or areas of snowstorm for Heilongjiang province.(6) There are two kinds of K index of snowstorm:the value of K index is very large, more than 8 Celsius degree,or the value of K index increase quickly, increasing range of 8 Celsius degree within 12 hours.On the vertical velocity field,from surface to upper level is the area of convergence ascending motion. At the middle and low level the relative humidity must be more than 80% of snowstorm,and at the upper level 70%.It is requiredθse/θz>0 in the snowstorm process, and the value ofθse on 850 hPa layer must be more than 4 Celsius degree, on 700 layer hPa is 8 Celsius degree,and on 500 hPa layer is above 16 Celsius degree.(7) It is well-distributed, continuous, extensive and low intensity on doppler radar echoes of snowfall.The position of front and the pressure are resolved from the doppler radar radial velocity fields. Clouds developping and moving are analyzed from the clouds image,and it is analyzed of water vapor sources and transportation from water vapor image.