大气沙尘的测定和分析研究

谈起"沙尘(暴)",住在我国北方干旱地区的人是比较熟悉的。大风卷起了地面的尘土沙粒,飞扬到天空,有时甚至遮蔽阳光,造成景色暗淡,浮尘满天,犹如蒙蒙细雨,随风降落,持续时间达1-2天,也有长达3-5天者,我国史书上称这种降尘现象为"雨土"。(一)大气沙尘指空气中夹带大量被风从地面卷起的沙粒和尘土,能在一定时间内悬浮于空气中的一种天气现象。它是一种分散体系,介质为空气,分散相是浮游于空气中的固体微粒,其粒度成分,据北京大兴县的测定表明,粒径0.01-0.005毫米颗粒占总量的56-71%,小于0.01毫米者占17-39%,大于0.05毫米者占14%。大气沙尘的高程分布,一般在离地表2米以上,其上限可达数十米或更高。

Determination of Dust-storm and Its Analytical Research

The dust-storm refers to a weather phenomenon: a large amount of dust-storm suspending in the air for a certain time.There must be two conditions for its formation: one is dry climate and strong wind; the other is sand particles susceptible to be blown away. Dust-storm often occurs in arid and semiarid zones of north and northwest China and cause severe damages to local industries, agriculture, communications and transportations. Therefore,great attention must be paid to this problem. In 1955-1956, airborne dust were determined at the Ying Shui Qiao area along the Baotou-Lanzhou railway by our institute. The institute adopted the methods of weight and precipitation and selected four levels of2,5,9and 13 meters, considered as the harmful height so as to determine airborne dust-storm. From the determined data,several laws of vertical distribution and of the relation between dust-storm in atmosphere and wind speed were obtained by using mathfmatic statistic techniques.They can also be referenced in similar areas.