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.Resultsalso 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.