Understanding the combined cloud-aerosol radiative effect for heterogeneous scenes
Thursday, 18 December 2014
Aerosol and cloud radiative effects are two of the largest uncertainties in surface energy budget estimates. In nature, aerosols and clouds can be highly variable spatially and temporally and they can co-exist. Therefore, understanding the combined radiative effects of clouds and aerosols – for example, for aerosol layers above homogeneous and inhomogeneous clouds, and for aerosol-immersed broken cloud fields – is essential to understanding the surface radiative energy budget as a whole. The Studies of Emissions and Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC4RS, 2013) experiment with its unique instrument combination, sampling strategy, and range of measurement conditions allows such studies. We use data from the Solar Spectral Flux Radiometer (SSFR, onboard the ER-2 and DC-8), the Enhanced MODIS Airborne Simulator (eMAS), the High Spectral Resolution Lidar (HSRL, DC-8) as well as the Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research (4STAR, DC-8) to identify cloud and aerosol radiative effects at the surface from both irradiance and radiance perspectives by means of their spectral signatures. For complex cloud scenes, we make use of 3-dimensional radiative transfer calculations to reproduce the measurements and to understand to which degree aerosol radiative effects can be isolated from those of the clouds by means of their distinct spectral signatures. We also discuss how the measured irradiance above and below cloud-aerosol layers systematically deviates from estimates that are obtained from one-dimensional radiative transfer models, and propose potential correction schemes that are applicable for correcting the effects of cloud inhomogeneities and aerosols.