PNNL

Abstract

The relationship between hemispherical sky cover and nadir-view cloud fraction is examined by using both model simulations and surface observations. Monte Carlo simulations of ground-based hemispherical measurements are based on four-dimensional cloud fields produced by a large eddy simulation model. Surface hemispherical observations were performed during the Atmospheric Radiation Measurement Program’s Cloudiness Intercomparison Intensive Operational Period. It is shown that (i) 15-minute averages of frequently sampled (30-second) sky cover provides a reasonable estimation of the cloud fraction for limited fields-of-view, (ii) this estimation can be substantially improved if additional information of the cloud aspect radio is incorporated into the retrieval process.