冬季风异常对中国春季北方沙尘日数的影响

基于1981~2010年台站沙尘观测资料和NCEP/NCAR再分析资料分析了我国北方春季沙尘日数的时空分布。沙尘频发区主要位于新疆南部和内蒙古西部,这两个中心全季沙尘日数均在10日以上。研究时段内北方沙尘日数呈显著减少趋势。相关分析发现,春季北方沙尘日数与前冬冬季风环流系统关系密切。春季沙尘日数偏多时,前冬东亚大陆陆地-西太平洋气压差较常年偏大,东亚大槽偏深,低层我国北方地区-蒙古国北风分量偏强,高层的东亚副热带纬向急流偏强、高纬度急流偏弱。上述环流型对应于强冬季风特征,反之亦然。进一步分析指出,冬季风强(弱)年,我国北方大部分地区春季低层辐散(辐合),降水偏少(多),低层北风偏强(弱),促使(抑制)春季沙尘的发生。

Influences of the East Asian Winter Monsoon on the Sand Storm Days in Northern China in Boreal Spring

Spatial and temporal distribution of sand storm days(SSDs) in northern China in boreal spring are analyzed based on the observed sand storm dataset in China and the NCEP/NCAR reanalysis projects during 1981-2010.There are two SSDs centers,one locates in the south of Xinjiang province,and the other lies in the west of Inner Mongolia.In each center,the SSDs are greater than 10.During the research period,the SSDs have remarkable descending trend.Statistical results indicate that the East Asian winter monsoon(EAWM) can influence the SSDs in northern China in boreal spring significantly.If the SSDs are above normal,the difference of sea level pressure between the Eurasia continent and the western Pacific is always greater in previous winter,the East Asia trough(EAT) at 500-hPa level is deeper,the northerly wind at lower-level troposphere in Mongolia and northern China is stronger,and the zonal westerly jet at higher-level troposphere at middle and higher latitudes are stronger and weaker,respectively,and vice versa.Results also show that the general circulation at lower-troposphere in northern China in spring is divergent(convergent) after a stronger(weaker) EAWM,and the precipitation in spring is less(greater),the northerly is stronger(weaker).This circulation pattern will impel(restrain) the occurrence of sand storm events in northern China.