基于绿洲尺度沙尘暴天气降尘的变化特征研究

Study on the Changing Characteristics of Falling Dust of a Sand-Dust Storm Based on Oasis Scale

以一次典型沙尘暴全过程的沉降沙尘为例,通过在策勒绿洲迎风向前缘、前缘向内2 km、中央及后缘不同位置设置取样点,研究了绿洲范围沙尘沉降的变化特征。结果表明:本次沙尘暴平均降尘量高达123.8 g/m2,沉降沙尘以细砂成分为主(约占77%),平均粒径偏粗,约为74μm。绿洲不同位置的沙尘沉降量以绿洲前缘最多(172.8 g/m2),向绿洲内部延伸,有逐渐减少的趋势,后缘位置最少,仅为75.8 g/m2;从绿洲前缘到内部,沙尘粒径逐渐变小,在前缘位置沙尘最粗,后缘的最细;而分选程度有逐渐变差的趋势,但变化不很显著,前缘到中央3个位置的分选较好,只有后缘点的分选较差;不同位置的粒度曲线基本都为稍呈负偏的常峰态分布,越深入绿洲内部,负偏程度越大。不同高度沉降沙尘亦有明显差异,随高度升高,沙尘平均粒径逐渐变小,沉降量显著减少,尤以低于2 m高度的递减率最为显著。

Take the falling dust of a typical sand-dust storm for example, the characteristics of dust deposition in different positions of Cele oasis is studied by setting up sampling points at the western oasis, going inward into oasis about two kilometers, the center and the eastern edge. The results show that： the average falling dust amount is 123.8 g/m^2, whose main component is fine sand （77%） with a coarse average grain-size about 74μm. The falling dust amount at western is the most （172.8 g/m^2） ,which is decreasing going inward into oasis and it is only 75.8 g/m^2 at eastern edge. From western oasis into inner, the average-size of falling dust is getting smaller and degree of sorting worse gradually, but the change is not significantly. Grain-size curves of different sampling points are all mesokurtic distribution, but slightly negative skewed and the more inward into oasis, the greater degree of negative skewed. The falling dust at different height is also significant different, whose average grain-size become smaller and falling dust amount, changing significantly at lower than two meters, become less gradually with height increasing.