Abstract:

Based on daily minimum temperature data of 45 observation stations in winter in Tianshan Mountains and northern Xinjiang from1961 to 2010, we presented the standards of 45 stations’low temperature day and the definition of regional persistent low temperature events (PLTE), and analyzed its spatial-temporal distribution and variation, further investigated circulation anomaly features of decadal change, large-scale circulation background, affecting system and cold air features on PLTE. The results are as follows. Low temperature day thresholds were elevated distribution pattern from northeast to southwest, minimum thresholds in Junggar Basin and Altay region of northern Xinjiang, with the values of -34℃ to -30℃, -24℃ to -20℃ in the western Yili region and Tianshan Mountains. PLTE appeared 35 times in the past 50 years, the occurrence frequencies are both 0.29 times per year in January and February, 0.14 times per year in December. Low temperature events’duration ranged from 5 d to 25 d, among 16 times over 10 d, 19 times from 5 d to 9 d. PLTE showed significant interannual and decadal decreasing trend, but no significant intensity change. PLTE were caused by large-scale circulation anomalies in the Northern Hemisphere, mainly the meridional circulation anomalies. They can be divided into West Siberian transverse trough type, Central Siberia trough east infalling type, north wind belt and northwest wind belt type and the north ridge-south trough (vortex) type. When cold air from the Arctic or Siberia enters into Xinjiang by super polar, northwest, eastward paths on 500 hPa, northern Xingjiang is controlled by -32℃ cold air and ground Mongolia High dominated in the Eurasia continent, high pressure center of over 1045 hPa locating in the Altay Mountains region, 1035 hPa cold high pressure controlling northern Xinjiang region.

Key words: northern Xinjiang, persistent low temperature events (PLTE), spatial and temporal distribution, circulation anomalies, cold air path