1990年北京降尘事件的天气动力条件及其化学元素特征

THE SYNOPTIC DYNAMIC CONDITION AND THE FEATURES OF CHEMICAL ELEMENTS OF THE DUSTFALL EVENT IN APRIL 1990 IN BEIJING

本文对1990年4月24—26日的席卷我国北部、中部的一次大范围尘暴降尘过程的天气动力条件做了诊断研究,并计算了北京地区采集的粉尘样品的化学浓度及相对于地壳平均含量的富集因子。作者指出,沙尘源地在内蒙古地区,与1958年3月北京降尘事件相比是一次在天气形势、沙尘源地和输送路径诸方面都有明显不同的另一种类型的降尘。

It is significant to study modern dustfall events to infer the dynamic process of historicduststorm and the reason of aeolian loess.There is a serious dustfall case in large area of North China during April 24—26,1990.The daily divergent field and vertical velocity field in the region of 75—125°E,30—50°Nare calculated.The active path of strong cold current,the rising and settling areas of thedust and the corresponding dynamic condition are analysed.The result shows that this pro-cess is quite different from that of the dustfall case in March 1958 in Beijing in terms of theair circulation,source area of dust and the transportation path.From analysing the chemical elements of powder samples collected in Beijing duringthe duststorm and calculating enrichment factor of each element relative to the average con-tent in the crust,it is shown that the elements whose EF_(crust) less than 5 in individual par-ticle size and total samples are Al,Si,K,Ca,Ti,V,Mn,Fe,Ni,Sr and Mg.The ratios of theelements Al,Fe,K and Ti are nearly equal to those of the elements in the chestnut inSiziwang Qi,Nei Monggol and have rather obviously different from those of Malan Loess,Xin-yuan,Xinjiang.This indicates that the source of descending dust material locates in NeiMonggol area.This is consistent with the conclusion by synoptic diagnostic analysis of actualweather process.