Effect of Specular High-Level Clouds on Scattered Solar Radiation Fluxes at the Zenith

The technique and results of a complex experiment on studying the effect of high-level clouds (HLCs) on the scattered solar radiation flux are described. Optical characteristics of clouds (backscattering phase matrix, optical depth, and scattering ratio) and their geometric characteristics (altitudes of the cloud base and top and vertical extent) were determined based on lidar data, and the scattered solar radiation flux over the lidar point of view was measured by a zenith pyranometer. It is shown that specular HLCs, i.e., clouds consisting of predominantly horizontally oriented ice crystals, significantly decrease the flux of scattered solar radiation incident on the Earth’s surface from the near-zenith sky as compared to HLCs with the same optical depth but a chaotic orientation of particles.