西北地区东部沙尘暴演变的气候型态与差异特征分析

利用西北地区东部近50年较完整的沙尘暴资料序列，在对沙尘暴年际变化特征分析的基础上，结合NCEP/NCAR月平均再分析资料和环流特征量资料，研究了西北地区东部沙尘暴过程发生频次由多到少及由少到多演变的基本环流型态及主要环流特征量的变化特征。结果表明：  近50年，西北地区东部年和春季沙尘暴过程发生频次在80年代中期出现由多到少的异常突变，1986年前，为多发阶段，其后，沙尘暴发生频次显著减少，处于少发阶段，90年代末，发生频次又明显增加；   沙尘暴频次突变前后极涡的强度、贝加尔湖到蒙古国的高度距平场以及副热带高压的强度和位置具有显著差异。同时，突变期间环流特征量的气候变率明显大于多年平均值，1986年到1987年及1998年到1999年，所选5类环流特征量的气候变率均出现了明显转折，对应同期西北地区东部沙尘暴过程频次出现了由多到少或由少到多的突变。进一步研究还发现，沙尘暴突变一般出现在多个环流特征量气候变率对应的同一个峰值（谷值）年。
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OCCURRENCE FREQUENCY OF SANDSTORMS AND THEIR CAUSING CLIMATE TYPES IN RECENT 50 YEARS IN EAST PART OF NORTH WEST CHINA

Statistic methods，such as synoptic analysis，correlation analysis，accumulated anomaly analysis，variation rate analysis，and Mann Kendall abrupt test are used with the combination of the monthly data of NCEP/NCAR to analyze sandstorms recorded during the past 50 years in the east part of North West China. The yearly variation characteristics of sandstorms show that in the recent 50 years，the occurrence frequency of sandstorm has an abrupt change in the middle 1980s. Before 1986，the frequency is high. After 1986，the frequency decreased obviously and maintained at a lower level till 1999，after which the frequency had an increase but still at a lower level than that before 1986.
The analysis on the main circulations at the same area shows that：  During the period with high sandstorm occurrence frequency the circulation intensity was at a high level，the high pressure ridge from Ural mountain to Caspian was stronger than average，and the trough in East Asia  was stronger than normal while its position moved a little westward. Cold air from Novaya Zemlya moved southward along the north air flow before the Ural high pressure ridge，then，influenced the east part of North West China  and caused sandstorms. During the period with low sandstorm occurrence frequency，the height anomaly field was opposite to that in high frequency period. Meanwhile，since 1961，the exponent of polarvortex index in the Northern Hemisphere，the position of trough in East Asia，the meridional cell index and area index in the West Pacific  Ocean，and the meridional cell index of Eurasia all show obvious fluctuant variation，among which the variation rage of Western Pacific  Subtropical High was the most prominent，and the position variation of the trough in East Asia changed the most lightly. During the transition period in the middle 1980′s，the variation rate of circulation intensity was obviously higher than average. The 5 selected circulations during 1986～1987 and 1998～1999 showed abrupt changes of intensity. Such transitions generally happened when many circulation characteristics ate at their peak(or trough)values.