Extended Abstract (212K)P3.8
Arctic mixed-phase cloud properties derived from surface-based sensors at SHEBA
Matthew D. Shupe, CIRES/Univ. of Colorado, Boulder, CO; and S. Y. Matrosov and T. Uttal
Arctic mixed-phase cloud macro- and microphysical properties are derived from a year of radar, lidar, microwave radiometer, and radiosonde observations made as part of the Surface Heat Budget of the Arctic (SHEBA) Program in the Beaufort Sea in 1997-1998. Mixed-phase clouds occurred 41% of the time and were most frequent in the spring and fall transition seasons. These clouds often consisted of a shallow, cloud top liquid layer from which ice particles formed and fell, although deep, multi-layered mixed-phase cloud scenes were also observed. Most of the observed mixed-phase clouds were 0.5-3 km thick, had a cloud base of 0-2 km, and resided at a temperature of -25 to -5 °C. Under the assumption that the large ice crystals dominate the radar signal, ice properties were retrieved from these clouds. The annual average ice particle mean diameter, ice water content, and ice water path were 93 µm, 0.027 g m-3, and 42 g m-2, respectively. These values are all larger than those found in single-phase ice clouds at SHEBA, suggesting that the presence of liquid water and warmer temperatures in mixed-phase clouds significantly support additional ice growth. The annual average microwave radiometer-derived liquid water path in mixed-phase clouds was 61 g m-2, which is larger than the average liquid water path observed in single-phase liquid clouds because the liquid layers in the mixed-phase clouds at SHEBA tended to be thicker than those in all-liquid clouds. Although mixed-phase clouds were observed down to temperatures of about -40 °C, the liquid fraction (ratio of condensed liquid water to total condensed water) increased, on average, from zero at -25 °C to one at -15 °C. The observations show a range of about 25 °C at any given liquid fraction and a phase transition relationship that changes moderately with season, both of which complicate the ability to accurately parameterize the partitioning of cloud phases based on temperature alone.
Poster Session 3, Formal Poster Viewing - Atmophere, Ice, Ocean
Wednesday, 12 January 2005, 2:30 PM-4:00 PM
Previous paper Next paper