On the Radiative Properties of Cirrus in the Window Region and Their Influence on Remote Sensing of the Atmosphere

Abstract

Transmission, emission and reflection characteristics of cirrus clouds in the 800?1200 cm?1 window region are obtained by means of solving the transfer of infrared radiation in the realistic moist and dry model atmospheres. These model atmospheres include the water vapor within, above and below the cirrus clouds which are assumed to be composed of randomly oriented cylinders. Results of the radiation parameters are presented in terms of the geometrical thickness of circus as well as the model atmospheres. The discrepancies between the transmission and emission for flux and those for the vertically emergent intensity are pointed out and discussed. It is shown that the radiative properties of cirrus depend strongly upon the particle concentration. For a typical cirrus with a thickness of 1 km whose concentration is 0.05 cm?3, the intensity transmission is about 0.65 with an emissivity of about 0.35. Further, based upon the theoretical analyses, the reductions in the effective temperature when cirrus clouds fill in the field of view of the radiometer reveal values from 0 to 60K. Having knowledge of the transmission and emission properties of cirrus clouds, it is demonstrated that the temperatures of the cloud and the underlying surface may be derived with reliable accuracy from meteorological satellites.