The Central Asian Vortexes Activity During 1971—2010

The synoptic scale system of cold vortex (the central Asian vortex) which occurs from east of Aral Sea to Xinjiang are frequently associated with Urals ridge, and its abnormal activity may cause many disasters such as rainstorm (snowstorm), low temperature and drought in Xinjiang, even affecting the weather and climate in east China. Using NCEP/NCAR reanalysis daily datasets from 1971 to 2010, the activity patterns, different moving tracks of the central Asian vortex and its influences on Xinjiang are analyzed. The result indicates that the central Asian vortex processes occur 305 times and 1166 days altogether during its strong period in the past 40 years. There are two high-frequency activity center along with the latitude: One distributes from 47.5°N to 55°N (north vortex) with 57% of the vortexes, and the other one distributes from 35°N to 47.5°N (south vortex), where 37% of the vortexes occurs. Northern vortexes change greatly in different seasons, accounting for 52% in summer. But southern vortexes occur evenly in different seasons, maybe a little more in autumn and spring. The mature period of the central Asian vortexes is 3.8 days on average, the frequency decreases rapidly with the mature period increasing: 56% vortexes sustain between 2 to 3 days, 27.5% maintain for 4 to 5 days and only 16.5% can last for more than 5 days. The vortexes show obvious monthly, seasonal, annual and interannual variation characteristics. It occurs the most in July and summer, and the least in April and winter, and the decadal increasing trend is significant. As to moving tracks, most of them move northeastward, eastward, southeastward and about 6% move little or move without obvious rules. Different moving track causes different weather in Xinjiang. About 68% of southeastward moving north vortexes and 30% of eastward and northeastward moving south vortexes have caused heavy precipitation in Xinjiang. The central Asian vortex has two types of influences on the weather in Xinjiang: One type brings heavy precipitation in Xinjiang, which is called wet vortex, and the other type causes cool wind and a long period of cold weather with little precipitation, which is called dry vortex. Dry vortexes account for 60% of the total and occur evenly in different seasons. However, the wet vortex occupies 40% of the total and is significantly different in different seasons. 57% wet vortexes occurs in summer and at this time there are more wet vortexes than dry vortexes, but for autumn, spring and winter, there are more dry vortexes than wet vortexes, and only 2% wet vortexes occur in winter. The seasonal variation patterns of wet vortexes are consistent with that of precipitation in Xinjiang.