The dust fall in Beijing, China on April 18, 1980

The granulometrical and mineralogical studies of the fallen dust collected at Beijing during dust-haze weather on April 18, 1980, show that it resembles the typical Pleistocene loess of China in composition and texture. The fallen dust is mainly composed of silt-size grains as are those of the loess. Quartz, feldspar, and carbonates constitute more than 90% of the total amount of the fallen dust, and they are subangular to subrounded. These characteristics of mineral grains of the fallen dust show evidently that it is an up-to-date loess. Meteorological study indicates that this loess was transported to Beijing by a sand and dust storm; dust-haze and dust-fall weather occurred during April 17-20, 1980, in northern China. The strong development of the Mongolian cyclone and the downward transport of momentum of the upper westerlies appeared on April 17 west of the huge loess plateau in central and western Inner Mongolia and He-xi (Kansu) Corridor and initiated the occurrence of the sandstorm. Through the upward motion and turbulent mixing, the sand and dust was enrolled into the westerly jet stream of the upper air. Thereafter, dust and sand in the upper-air jet stream rapidly shifted, spread, and subsided southeastward over the loess plateau and arrived in Beijing on April 18, after it had traveled about 1,500 km east from its source area. The synoptic analysis together with the study of the dust provides an example of recent loess deposition and a possible model of eolian loess transportation and deposition.