HR: 1340h
AN: A23C-0969    [Abstracts]
TI: Mixed-Phase Cloud Properties Derived From Remote-Sensors in the Western Arctic
AU: * Shupe, M
EM: matthew.shupe@noaa.gov
AF: Cooperative Institute for Research in Environmental Sciences, University of Colorado and NOAA/ETL, 325 Broadway, Boulder, CO 80305 United States
AU: Matrosov, S
EM: sergey.matrosov@noaa.gov
AF: Cooperative Institute for Research in Environmental Sciences, University of Colorado and NOAA/ETL, 325 Broadway, Boulder, CO 80305 United States
AU: Uttal, T
EM: taneil.uttal@noaa.gov
AF: NOAA Environmental Technology Laboratory, 325 Broadway, Boulder, CO 80305 United States
AB: Despite the frequent occurrence of mixed-phase clouds in the Arctic, these clouds are still poorly understood and misrepresented in models at all scales. In particular, the proper partitioning of cloud phases is important when considering the unique radiative properties of liquid droplets and ice crystals, the impact of phase on precipitation processes, and the sensitivity of phase transitions to possible climate changes. Some deficiencies in our understanding of Arctic mixed-phase clouds can be addressed by examining cloud observations from the Atmospheric Radiation Measurement Program's North Slope of Alaska (NSA) site and the Surface Heat Budget of the Arctic (SHEBA) Program. Many cloud properties have been observed by, or retrieved from, remote-sensors at these sites, including cloud radar, depolarization lidar, microwave radiometer, and radiosondes. A summary of mixed-phase cloud macro- and microphysical properties derived from observations at the NSA (1998-2004) and SHEBA (1997-1998) sites is provided here. Mixed-phase clouds occurred an average of 46% of the time at the NSA and 41% of the time at SHEBA over the observed time periods. At both sites, nearly 60% of the observed clouds were of the mixed-phase classification. Over the annual cycle, the monthly mixed-phase cloud fraction was at a maximum during the spring and fall transition season; however, this annual trend was shifted approximately 1-2 months earlier for the SHEBA site in the Arctic Ocean relative to the coastal NSA site. On average, the mixed-phase clouds observed over the six-year period at the NSA were slightly lower (mean cloud base of 0.6 vs. 0.9 km) and thinner (1.5 vs. 1.9 km) than those observed during the one year period at SHEBA. However, these clouds were present at similar temperature ranges at both sites, varying from average winter minima of -25 to -20 °C to average summer maxima near -10 °C. The annual average mixed-phase cloud temperature at both sites was -14 °C. In terms of cloud microphysical properties, the annual average ice particle mean diameter was about 90 μm at both sites, while the average ice water path (IWP) was larger at the NSA (55 vs. 42 g/m²). Similarly, the average liquid water path (LWP) observed in mixed-phase clouds at the NSA was about 10% larger than at SHEBA (70 vs 61 g/m²). At both observation sites, the amount of liquid relative to ice in mixed-phase clouds (i.e., the liquid fraction, or LWP/(LWP+IWP)) broadly increased with cloud top temperature. The annual average relationship between the liquid fraction and temperature, for both NSA and SHEBA, shows a consistent and relatively steep decrease from nearly all liquid at -13 °C to nearly full glaciation at -24 °C. However, at any given liquid fraction, the temperature varies over approximately 20-25 °C, which complicates the ability to accurately parameterize the partitioning of cloud phases based on temperature alone. These data support the notion that cloud phase parameterizations based on additional parameters will likely be necessary to capture the natural variability of Arctic cloud phase distributions.
UR: http://www.etl.noaa.gov/arctic
DE: 0320 Cloud physics and chemistry
DE: 3310 Clouds and cloud feedbacks
DE: 3360 Remote sensing
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005