A study of radiative properties of fractal soot aggregates using the superposition T-matrix method

We employ the numerically exact superposition T-matrix method to perform extensive computations of scattering and absorption properties of soot aggregates with varying state of compactness and size. The fractal dimension, D_f, is used to quantify the geometrical mass dispersion of the clusters. The optical properties of soot aggregates for a given fractal dimension are complex functions of the refractive index of the material m, the number of monomers N_S, and the monomer radius a. It is shown that for smaller values of a, the absorption cross section tends to be relatively constant when D_f<2 but increases rapidly when D_f>2. However, a systematic reduction in light absorption with D_f is observed for clusters with sufficiently large N_S, m, and a. The scattering cross section and single-scattering albedo increase monotonically as fractals evolve from chain-like to more densely packed morphologies, which is a strong manifestation of the increasing importance of scattering interaction among spherules. Overall, the results for soot fractals differ profoundly from those calculated for the respective volume-equivalent soot spheres as well as for the respective external mixtures of soot monomers under the assumption that there are no electromagnetic interactions between the monomers. The climate-research implications of our results are discussed.     

散射大气对脉冲紫外光传输时间特性研究

介绍基于椭球坐标系的单次散射近似模型基础上,定量分析脉冲紫外光在散射大气中传输特性,具体讨论了传输距离及能见度等因素对脉冲紫外光传输特性的影响。最后开展了脉冲紫外光展宽初步实验研究,其实验结果与单次近似结果符合较好,从而指导了紫外光信息传输系统的设计工作。     

Temperature dependence of ice optical constants: Implications for simulating the single-scattering properties of cold ice clouds

For a spectrum from ultraviolet to microwave and a temperature range from 160 to 270 K, the optical constants of water ice are compiled on the basis of the Kramers-Kronig relation in conjunction with existing datasets reported in literature. Significant temperature dependence is observed in both the mid-infrared and longer wavelengths. A sensitivity study at wavelengths in the infrared split window region indicates that the temperature dependence of the single-scattering properties of ice crystals is not negligible. Thus, it is necessary to take into account the temperature dependence of ice optical constants when simulating the radiative properties of cirrus clouds for various applications to remote sensing under cirrus cloud conditions.