A COMPARISON OF EVAPORATIVE COOLING WITH INFRARED HEATING BENEATH A CIRRUS CLOUD

Data for this study were collected by the instruments mounted on the NCAR King Air and rawinsonde during the First ISCCP (International Satellite Cloud Climatology Project) Regional Experiment (FIRE) on 19 October, 1986. The main purpose of this study is to understand the basic concept of evaporative cooling in a dry layer below a cirrus generating cell. Relative humidity with respect to liquid water RH(w) and temperature lapse rate gamma(e) below the cirrus base at about 6.7 km were about 40% and 3.7 degrees C km(-1), respectively. Evaporative cooling rate (ECR) in the 1.5 km thick subcloud layer was estimated to be approximately 0.1 to 2 degrees C h(-1) and it was found to be comparable with the infrared heating rate calculated from radiation measurements. Because of ice crystal evaporation, RH(w) in the same layer may reach saturation with respect to ice in 1.5 hours.