Radiative Properties of Cirrus Clouds Derived from Surface Interferometric Measurements

Abstract

Beam transmittance, emittance, reflectance, and outgoing radiance are inferred from interferometric measurements in the infrared window region for 14 temperate continental and 12 subtropical cirrus cloud cash observed during FIRE II at Parsons, Kansas (37°18?N, 95°07?W), and the ASTEX at Porto Santo, Madeira (33°5?N, 16°21?W). Cirrus emittances were found to span nearly the entire range from 0 to 1 for cloud systems in each location. Spectrally averaged volume extinction coefficients of 0.19 and 0.62 km?1 were found for the respective continental and subtropical samples. A delta-Eddington routine was incorporated into the inference technique to examine the sensitivity of the inferences to the upwelling surface and subcloud-layer emission reflected by the cloud assuming spherical and nonspherical cloud particles. Including reflectance had only a small effect on the spectrally averaged values of the radiative parameters; however, the slope of outgoing longwave radiation across the window region was altered with the introduction of smaller particles. The iterative method is structured in a manner that does not constrain the transmittances of the clear atmosphere to line-by-line model results. Inferred emittances and extinction coefficients are compared to previously published results.