Retrieval of polar stratospheric cloud microphysical properties from lidar measurements: Dependence on particle shape assumptions

Computational simulations have been performed to deduce the dependence of the microphysical analysis of polar stratospheric cloud (PSC) optical data measured with lidar on the assumptions made about particle shape. In a forward model, PSCs are modeled as crystalline and liquid particles in order to generate synthetic optical properties. The parameterization scheme of the PSC microphysical properties allows for coexistence of up to three different particle types with size‐dependent shapes; optical properties of individual crystals, specifically hexagonal and asymmetric polyhedral crystals, are determined using the finite difference time domain (FDTD) method. The set of calculated PSC optical properties is selected based on the wavelengths and measurement capabilities of lidar instruments that are typically used to monitor stratospheric aerosols, such as the Airborne Raman Ozone and Temperature Lidar (AROTEL) and the NASA Langley Differential Absorption Lidar (DIAL) onboard the NASA DC‐8 during the Stratospheric Aerosol and Gas Experiment (SAGE) Ozone Loss Validation Experiment (SOLVE) campaign in winter 1999/2000. The retrieval process then inverts these synthetic measurement data using a model approach in which the PSC particles are represented purely by an ensemble of spheroids, and the differences between initial and retrieved microphysical properties are examined. The model simulations show that under the assumption of spheroidal particle shapes, surface area density and volume density of leewave PSCs are systematically smaller by, respectively, ∼10–30% and ∼5–25% than the values found for mixtures of droplets, asymmetric polyhedra, and hexagons.