Absorption of solar radiation by the atmosphere as determined using satellite, aircraft, and surface data during the Atmospheric Radiation Measurement Enhanced Shortwave Experiment (ARESE)

Data sets acquired during the Atmospheric Radiation Measurement Enhanced Shortwave Experiment (ARESE) using simultaneous measurements from five independent platforms (GOES 8 geostationary satellite, ER-2, Egrett and Twin Otter aircraft, and surface) are analyzed and compared. A consistent data set can be built for selected days during ARESE on the basis of the observations from these platforms. The GOES 8 albedos agree with the ER 2, Egrett, and Twin Otter measured instantaneous albedos within 0.013 +/- 0.016, 0.018 +/- 0.032, and 0.006 +/- 0.011, respectively. It is found that for heavy overcast conditions the aircraft measurements yield an absorptance of 0.32 +/- 0.03 for the layer between the aircraft (0.5-13 km), while the GOES 8 albedo versus surface transmittance analysis gives an absorptance of 0.33 +/- 0.04 for the total atmosphere (surface to top). The absorptance of solar radiation estimated by model calculations for overcast conditions varies between 0.16 and 0.24, depending on the model used and on cloud and aerosol implementation. These results are in general agreement with recent findings for cloudy skies, but here a data set that brings together independent simultaneous observations (satellite, surface, and aircraft) is used. Previous ARESE results are reexamined in light of the new findings, and it is concluded that the overcast absorptance in the 0.224-0.68 mu m spectral region ranges between 0.04 +/- 0.06 and 0.08 +/- 0.06, depending on the particular case analyzed. No evidence of excess clear-sky absorption beyond model and experimental errors is found.