An observational study of aerosol and turbulence properties during dust storms in northwest China

Abstract

Since late 2003, measurements of aerosol properties and meteorology have been made at three sites, Minqin, Jiuquan and Dunhuang, in the border areas of the Gobi and Taklimakan Deserts in the northwest of China as part of an observational program for Asian Dust Storms (ADS). The aerosol observations include mass concentration and optical depth, and the meteorological observations include both mean and turbulent quantities. The data from a three‐year period (2004–2007) have been analyzed to characterize aerosol and meteorological conditions during dust storms. The results show that during ADS the aerosol mass concentration (PM10) can reach above 7∼8 mg m−3, 10∼100 times of that on clear days, and the scatter coefficient of fine particles (PM2.5) is 2000∼2500 10−6 m−1, 20∼25 times of the clear day values. There is a dramatic reduction in the visibility during dust storms with average visibility about 2 km, which is only 1/20∼1/30 of that on clear days. The aerodynamic roughness is 0.018 and 0.046 m for the Taklimakan and Gobi Deserts respectively, and the friction velocity is about 0.71 and 0.56 m s−1 during ADS periods, doubling the value found on quiescent days. Turbulence in the lower atmosphere is more intense during ADS period due mainly to increased vertical wind shear associated with strong winds. The large‐scale circulation patterns show that during the ADS conditions the Gobi Desert is typically in the path of cold air from high latitudes moving toward the south or southeast and the data suggest that there is a declining trend for dust storms during the past 5 decades.