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

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 mum and ice water contents up to 0.1 g/m(3), 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 mum, liquid water contents up to 0.7 g/m(3), 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 similar to 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.