Refinement of global ice microphysics using spaceborne active sensors

摘要

This work improved on the lidar and radar retrieval algorithm developed by Okamoto et al. to extend the applicability of the microphysical retrieval scheme from the cloud region with lidar‐radar overlap to lidar‐ or radar‐only cloud regions with an available radar‐lidar overlap area in the vertical profile by use of the Levenberg‐Marqardt method. The algorithm was formulated to efficiently reflect the information from the lidar‐radar overlap region to the microphysical retrieval at the radar‐ or lidar‐only region to avoid the use of a prescribed parameterization among the observables and cloud microphysics. The algorithm incorporated particle‐type discrimination before the microphysical retrieval, consistent with the theoretical treatment of two‐dimensional (2‐D) and three‐dimensional (3‐D) ice particle mixtures in the radar and lidar forward models and the combined use of three observables (the radar reflectivity Z_e, the lidar backscattering coefficient β, and the depolarization ratio δ) for the lidar‐ or radar‐only cloud regimes. A full one‐to‐one comparison of the retrieved microphysical properties with the results of the previous algorithm revealed that r_(eff) could be retrieved consistently within about 10 uncertainty, on average. The ice water content (IWC) retrieval also performed well, except for extreme cases, and the uncertainties of IWC as well as r_(eff) were within about 40 for the radar‐only region, despite the depth of the radar‐only cloud layers. When considering only the cloud region with lidar‐radar overlap, the zonal mean profiles of r_(eff) may be slightly larger and IWC may be slightly smaller when considering attenuation caused by the lidar‐only region, which occasionally occurs above the region of lidar‐radar overlap.