10/30/2013
New Approach for Simultaneously Retrieving Cloud Brightness and Amount from Surface Measurements
Summary
As climate changes, clouds respond in multiple ways. Observing these various responses consistently is challenging, making the science of cloud-climate interactions especially difficult. Two ways that clouds respond to climate change include the fraction of a region covered by clouds, and cloud brightness resulting from changes in cloud droplet number or phase (i.e., water versus ice). Surface-based measurements of sunlight or “solar radiation” contain valuable information needed to understand these cloud properties, but they have not been fully utilized. Department of Energy researchers have developed a new approach that simultaneously infers cloud brightness (or “albedo”) and cloud fraction from surface-based measurements of solar radiative fluxes. The radiative fluxes include both the “direct” incoming radiation, as well as “diffuse” radiation that includes radiation scattered from clouds, land, and atmospheric particles. Cloud fraction is primarily determined by the difference between all-sky and clear-sky “direct” radiation. The cloud brightness calculation incorporates further information from diffuse as well as direct radiation. The new method is tested using a computer algorithm that combines various types of measurements, including both satellite and surface measurements. The new approach demonstrates the utility of partitioning total radiation into direct and diffuse components, eliminating the potential contamination of errors in existing approaches that retrieve cloud fraction and cloud albedo separately. The method also has the potential for a consistent model evaluation.
References
Xie, Y., and Y. Liu. 2013. “A New Approach for Simultaneously Retrieving Cloud Albedo and Cloud Fraction from Surface-Based Shortwave Radiation Measurements,” Environmental Research Letters 8, 044023. DOI:10.1088/1748-9326/8/4/044023.