黄土高原半干旱区典型日吸收性气溶胶综合观测分析

利用兰州大学半干旱气候与环境观测站的太阳光度计、激光雷达、微波辐射计综合观测资料，结合辐射传输模式分析了该地区秋季典型日2012年9月3~4日、21日和28日气溶胶物理特性、垂直分布特征，及其与气象条件的关系。研究时期的气溶胶主要为局地沙尘与人为污染混合气溶胶，吸收性明显，尺度较小。其中，4日西北风增强，远距离传输沙尘气溶胶，气溶胶光学厚度最大，粒子尺度明显增大。尝试利用灰色关联度法确定参考高度，分别为7.41 km、8.47 km、7.13 km和7.66 km，反演气溶胶消光系数，由此积分得到的光学厚度与太阳光度计观测值相关性可达0.975，反演效果较好。研究时期气溶胶的抬升主要受白天热力湍流作用，边界层发展，气溶胶向上传输，每日12时（当地时间，下同）至14时传输至最大高度，气溶胶抬升的高度对应大气加热率的高值区，低层加热率可达1 K d-1。气溶胶在大气层顶和地面造成负辐射强迫，分别为-12.707 W m-2、-25.398 W m-2，大气中表现为正辐射强迫，为12.692 W m-2，大气层顶的辐射强迫对气溶胶的物理特性最为敏感，当气溶胶吸收性明显时，大气层顶的瞬时辐射强迫会出现正值。

Comprehensive Observations and Analysis of Absorptive Aerosols on Typical Days in the Semi-arid Region of the Loess Plateau

The physical properties of absorptive aerosols on typical autumn days, i.e. 3-4, 21, and 28 September 2012, in the semi-arid region of the Loess Plateau are analyzed using a radiative transfer model and comprehensive observation data provided by the SACOL (Semi-arid Climate and Environment Observatory of Lanzhou University). The data include simultaneous observations of sunphotometer, lidar, and microwave radiometer. The relationship between aerosols and meteorology situation is studied. Local dust mixed with anthropogenic aerosols form the major source of aerosols during the period, which have obvious absorptive effects and the aerosol particle sizes are commonly small. However, due to the increased northwesterly winds on the 4 September 2012, there existed more dust transport through long distance, and the aerosol optical depth was the largest and the particle size increased sharply. The reference height was determined to be 7.41 km, 8.47 km, 7.13 km, and 7.66 km, respectively by the gray pertinence method, and the extinction coefficient was also retrieved. The AOD (Aerosol Optical Depth) calculated from the retrievals agreed well with observations from the sunphotometer with a correlation coefficient up to 0.975. The aerosol uplift is mainly attributed to effects of thermal turbulences during the daytime in the study period, when the aerosols were transported upward as the boundary layer developed and reached the maximum height from 1200 LT (Local Time) to 1400 LT every day. Meanwhile, the altitude of aerosols could reach corresponded to level of high heating rate, which at lower levels could be up to 1 K d⁻¹. The aerosols had negative radiative forcing at the top of the atmosphere and the surface with the daily average values of 12.707 W m⁻² and −25.398 W m⁻², but they had positive radiative forcing in the atmosphere with a daily average value of −12.692 W m⁻². The radiative forcing at the top of the atmosphere is most sensitive to aerosol properties, and the aerosol forcing would be positive at the top of the atmosphere if the aerosols have obvious absorption effects.