Irregularly shaped ice aggregates in optical modeling of convectively generated ice clouds
- 作者：Hiroshi Ishimoto ; hishimot@mri-jma.go.jp ; Kazuhiko Masuda ; Yuzo Mano ; Narihiro Orikasa ; Akihiro Uchiyama
- 关键词：Light scattering ; Irregularly shaped particles ; Cirrus
- 刊名：Journal of Quantitative Spectroscopy and Radiative Transfer
- 出版年：2012
- 期刊代码：70_00224073
- 类别：ch
- 出版时间：May, 2012
- 卷：113
- 期：8
- 页码：632-643
- 文件大小：1137 K
摘要
We propose a model of irregular shaped ice particles for satellite and ground-based cloud remote sensing applications. Microphysical observations have shown that ice particles generated in convective clouds tend to have highly irregular structures as a result of aggregation process. To simulate such complex structures, we used spatial Poisson-Voronoi tessellations. Furthermore, we adopted fractal-like shapes that were consistent with the proposed mass-dimension and area ratio-dimension relationships of measured cirrus particles. Single-scattering properties of the modeled 鈥淰oronoi aggregates鈥?at visible wavelengths with size parameters up to 2246 were estimated from numerical calculations using the finite-difference time-domain method and the geometrical-optics integral-equation method. The phase functions for randomly oriented Voronoi aggregates showed features with no halos in the forward-scattering direction and a flat angular dependence in the side-to-backscattering directions. These characteristics and resultant asymmetry factors agreed with those of measured ice particles. Moreover, we confirmed the weak size and shape dependences of these scattering properties for the Voronoi aggregates, as well as high backscattering depolarization ratios and low linear polarizations.