Statistical Properties of Horizontally Oriented Plates in Optically Thick Clouds From Satellite Observations

Specular reflection from horizontally oriented plates (HOPs) has significant effects on lidar backscatter. The intensity of specular reflection from HOPs is high in warm mixed-phase clouds and low in cold ice clouds. The theoretical simulations of lidar backscatter and depolarization ratio are consistent with spaceborne measurements for optically thick mixed-phase and ice clouds if an equivalent percentage of HOPs of 0.08%-0.3% is assumed. Based on the joint probability density function of the attenuated backscatter and depolarization ratio observed by the Cloud-Aerosol Lidar with Orthogonal Polarization aboard the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations platform, it is estimated that HOPs exist in approximately 60% of optically thick (τ > 3) ice and mixed-phase cloud layers. The cloud-layer temperature is the primary factor affecting the distribution of HOPs. Specifically, HOPs exist in approximately 88% of optically thick ice and mixed-phase cloud layers warmer than -30°C, in approximately 84% of ice and mixed-phase cloud layers between -30°C and -45°C, and in approximately 29% of cold ice cloud layers below -45°C.