Backscattering properties of randomly oriented hexagonal hollow columns for lidar application

Abstract

The study of the optical properties of cirrus clouds is necessary to improve the accuracy of interpreting data from space lidars and ground-based lidar networks. Existing databases of backscattering properties do not include data on hollow columns. In this paper, the backscattering properties of randomly oriented hollow column ice crystal particles in cirrus at wavelengths of 355 nm, 532 nm, and 1064 nm have been investigated. The backscattering cross section (M11), depolarization ratio (δ), lidar ratio (S), and color ratio (χ) of randomly oriented hollow columns with sizes ranging from 10–316.23 µm are calculated within the framework of the physical optical approximation (PO). For the first time, we introduce the concept of modal hollow columns (MHC) suitable for mid-latitude regions, which simplifies the description of hollow ice crystals in nature. It is found that when the mixing proportion of MHC and solid columns (SC) reaches 50%, the mixing ratio can be distinguished by the lidar ratio for a wavelength of 1064 nm and by the χ(1064,532)-δ(532) relation.