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Aerosol properties in a Chinese semiarid region

机译：中国半干旱地区的气溶胶特性

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Aerosol optical properties and atmospheric water vapor content for 1999-2000 were obtained from ground-based solar radiometer measurements in Dunhuang, China. Seasonal changes of aerosol optical depth (AOD) and Angstrom wavelength parameter (ALPHA) were observed. Large values of AOD (at 500 nm) greater than 1.0 combined with low values of ALPHA less than 0.2 were mainly observed in spring and summer, which is consistent with the seasonal dust production from Gobi and Taklamaken deserts. The maximum monthly average of AOD was around 0.37 and occurred in the April of 1999, which was more than three times larger than the minimum monthly average in the November of 2000 (around 0.115). Thirty-three percent and 49% of observations of AOD in autumn and winter was larger than 0.2, respectively, whereas in spring, the percentage was approximately 63%. There was a large spread in ALPHAs in all seasons when AODs were less than 0.2. With the increase of AOD, ALPHAs decreased rapidly and were around zero finally. The large spread of ALPHA for low AODs and the domination of low turbidity in Dunhuang (nearly half of AODs less than 0.2) resulted in the negligible seasonal change of ALPHA. The domination of coarse particles over fine particles was also shown in aerosol size distribution retrievals, with the volume concentration ratio of coarse to fine particles being nearly 30. The volume mean radii and standard deviation of size distribution showed an insignificant correlation with AOD based on the analysis of all available retrievals, illustrating that it is suitable to use a fixed size model in the analysis of the dust climate forcing. During the dust outbreak episode, a rapid increase of AOD and a decrease of ALPHA were observed, ALPHA being usually less than 0.2 and even negative occasionally. The interesting result was that the volume mean radii of size distribution during the dust outbreak episode increased remarkably with the dust loading, which indicated that a dynamic size model should be used in the simulation of dust effects on meso-scale weather system in the semiarid region. The distinct seasonal change of water vapor content was observed, with high water vapor contents occurred in summer. The influence of water vapor on aerosol properties was absent due to the low humidification capability of dust aerosols and the different seasonal variation of aerosol properties and water vapor content.
机译：1999-2000年的气溶胶光学特性和大气水汽含量来自中国敦煌的地面太阳辐射计测量结果。观察到气溶胶光学深度（AOD）和埃波长参数（ALPHA）的季节性变化。主要在春季和夏季观察到大于1.0的较大的AOD值（在500 nm处）和小于0.2的较低的ALPHA值，这与戈壁和塔克拉玛肯沙漠的季节性粉尘产生是一致的。 AOD的最高每月平均值约为0.37，发生在1999年4月，是2000年11月的最低每月平均值（约为0.115）的三倍以上。秋季和冬季，AOD观测值的33％和49％分别大于0.2，而在春季，这一百分比约为63％。当AOD小于0.2时，所有季节的ALPHA分布都很大。随着AOD的增加，ALPHA迅速下降，最终达到零。 ALPHA在低AOD值中的广泛传播以及低浊度在敦煌占主导地位（近AOD值的一半低于0.2）导致ALPHA的季节变化可忽略不计。在气溶胶粒度分布检索中还显示了粗颗粒对细颗粒的支配性，粗颗粒与细颗粒的体积浓度比接近30。基于平均粒径，体积平均半径和尺寸分布的标准偏差与AOD无关紧要。分析所有可用的检索结果，说明在粉尘气候强迫分析中使用固定大小的模型是合适的。在粉尘暴发期间，观察到AOD迅速增加而ALPHA减少，ALPHA通常小于0.2，有时甚至为负值。有趣的结果是，沙尘暴爆发期间尘埃分布的体积平均半径随着尘埃负荷的增加而显着增加，这表明应该使用动态尺寸模型来模拟半干旱地区中尺度天气系统的尘埃影响。观察到水汽含量有明显的季节性变化，夏季水汽含量较高。由于粉尘气溶胶的加湿能力低以及气溶胶特性和水蒸气含量的不同季节变化，因此没有水蒸气对气溶胶特性的影响。

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