Cloud water contents and hydrometeor sizes during the FIRE Arctic Clouds Experiment

Abstract

During the year‐long Surface Heat Budget of the Arctic Experiment (1997–1998) the NOAA Environmental Technology Laboratory operated a 35‐GHz cloud radar and the DOE Atmospheric Radiation Measurement Program operated a suite of radiometers at an ice station frozen into the drifting ice pack of the Arctic Ocean. The NASA/FIRE Arctic Clouds Experiment took place during April‐July 1998, with the primary goal of investigating cloud microphysical, geometrical, and radiative properties with aircraft and surface‐based measurements. In this paper, retrieval techniques are utilized which combine the radar and radiometer measurements to compute height‐dependent water contents and hydrometeor sizes for all‐ice and all‐liquid clouds. For the spring and early summer period, all‐ice cloud retrievals showed a mean particle diameter of about 60 μm and ice water contents up to 0.1 g/m3, with the maximum sizes and water contents at approximately one fifth of the cloud depth from the cloud base. The all‐liquid cloud retrievals had a mean effective particle radius of 7.4 μm, liquid water contents up to 0.7 g/m3, and a mean droplet concentration of 54 cm−3. Maximum retrieved liquid drop sizes, water contents, and concentrations occurred at three fifths of the cloud depth from the cloud base. As a measure of how representative the FIRE‐ACE aircraft flight days were of the April‐July months in general, retrieval statistics for flight‐day clouds are compared to the mean retrieval statistics. From the retrieval perspective the ice particle sizes and water contents on flight days were ∼30% larger than the mean retrieved values for the April‐July months. Retrieved liquid cloud parameters during flight days were all about 20% smaller. All‐ice and/or all‐liquid clouds acceptable for these retrieval techniques were observed about 34% of the time clouds were present; at all other times, mixed‐phase clouds precluded the use of these single‐phase retrieval techniques.