Infrared Radiative Properties of Summertime Arctic Stratus Clouds

Abstract

Aircraft measurements of infrared radiation and cloud microphysics that were collected during the June 1980 Arctic Stratus Experiment are presented and analyzed with the aid of an infrared radiative transfer model. The radiation measurements were obtained with the NCAR Electra's Eppley pyrgeometers and a Barnes PRT-6 radiometer, and the cloud particle observations were obtained with the Knollenberg FSSP and 200X probes. The data were used to derive values of cloud emittances, mass and volume absorption coefficients, cloud reflectances, cooling rates and radiative extinction lengths. These parameters were found to be strongly dependent on the cloud drop size distribution, and a parameterization of the absorption coefficient in terms of liquid water content and droplet equivalent radius is presented. The window reflectance of the clouds was determined to be between 6.4 and 8.8%.