关键词: 罕见降雪, 低温, 天气气候分析

Abstract:

By using NCEP/NCAR data，this paper analyzed the circulation background and the physical quantity characteristic of the rare snowy and low temperature weather event occurred on January 10 to 31 in 2008 in eastern region of Gansu province． The results indicated that during this weather process，the Siberia ridge was powerful，the trough in the west Qinghai － Tibet Plateau and the weak ridge in East China persisted，with the abnormally northerly location of East Asian trough and the strong south branch jet stream in Qinghai － Tibet plateau，the cold air mass was active which controlled the middle of Asia and the North China and Northwest China．The temperature at the level of 700 hPa decreased strongly． The center of 700 hPa relative humidity positive anomaly was located in the eastern of Northwest China，and 500 hPa relative humidity was more than 70%． The 700 hPa wind had obvious shear in the range of98° － 110°E and 35° － 40°N． There was transfer and convergence of moisture at the lower level during the period of snow falling，but smaller than that of autumn precipitation． The vorticity was positive from700 to 200 hPa．

Key words: the rare snowfall, low temperature, synoptic and climatic analysis