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

Data for this study were collected by the instruments mounted on the N CAR King Air and rawinsonde during the First ISCCP (International Sate llite Cloud Climatology Project) Regional Experiment (FIRE) on 19 Octo ber, 1986. The main purpose of this study is to understand the basic c oncept of evaporative cooling in a dry layer below a cirrus generating cell. Relative humidity with respect to liquid water RH(w) and temper ature lapse rate gamma(e) below the cirrus base at about 6.7 km were a bout 40% and 3.7 degrees C km(-1), respectively. Evaporative cooling r ate (ECR) in the 1.5 km thick subcloud layer was estimated to be appro ximately 0.1 to 2 degrees C h(-1) and it was found to be comparable wi th the infrared heating rate calculated from radiation measurements. B ecause of ice crystal evaporation, RH(w) in the same layer may reach s aturation with respect to ice in 1.5 hours.