Cloud shortwave spectral radiative properties: Airborne hyperspectral measurements and modeling of irradiance

The design, construction, and performance of a solar spectral irradiance system for the National Center for the Atmospheric Research (NCAR) High Performance Instrumented Airborne Platform for Environmental Research (HIAPER) aircraft is described. The redesign of the integrating sphere baffling system used to for the measurement of solar irradiance is also described. The new baffle has improved the cosine response, reducing the error three-fold from the maximum error of the original design. Two aircraft studies from the Tropical Composition, Cloud and Climate Coupling Experiment (TC4) of cloud spectral (400-2100 nm) radiative properties are presented. Ice cloud single scattering properties are validated with detailed radiative transfer modeling of ice cloud spectral albedo and aircraft measurements of the same. Liquid water cloud absorption is examined with spectrally resolved flux divergence (layer absorption) measurements of marine stratus clouds. Mie calculations of cloud single-scattering properties are combined with radiative transfer calculations predict spectral absorptance. Model results are compared with cloud absorptance derived from aircraft measurements. Model results illustrate the spectral dependence of cloud absorption on optical thickness, effective radius, and the absorbing aerosols. Spectral measurements demonstrate the dependence of integrated cloud absorption on varying water vapor amount. A novel technique for single aircraft measurements of flux divergence is described