Spectral signature of column solar radiation absorption during the Atmospheric Radiation Measurement Enhanced Shortwave Experiment (ARESE)

Abstract

Spectral and broadband shortwave radiative flux data obtained from the Atmospheric Radiation Measurement Enhanced Shortwave Experiment (ARESE) are compared with 3-D radiative transfer computations for the cloud field of October 30, 1995. Because the absorption of broadband solar radiation in the cloudy atmosphere deduced from observations differs from that modeled by 135 W m-2, we performed a consistency analysis using spectral observations and the model to integrate for wavelengths between the spectral observations. To match spectral measurements, aerosols need a reduction in both single-scattering albedo (from 0.938 to 0.82) and asymmetry factor (from 0.67 to 0.61), and cloud droplets require a threefold increase in coalbedo. Even after modifying the model inputs and microphysics the difference in total broadband absorption is still of the order of 75 W m-2. Finally, an unexplained absorber centered near 1.06 μm appears in the comparison that is much too large to be explained by any known atmospheric process. Copyright 2000 by the American Geophysical Union.