HR: 1340h
AN: A23C-0963    [Abstracts]
TI: The Potential Importance of the Cloud Processing of Aerosol in Mesoscale Simulations of Mixed-Phase Arctic Stratus
AU: * Avramov, A
EM: lz4ax@psu.edu
AF: Department of Meteorology Pennsylvania State University, 503 Walker Building, University Park, PA 16802
AU: Harrington, J Y
EM: harring@mail.meteo.psu.edu
AF: Department of Meteorology Pennsylvania State University, 503 Walker Building, University Park, PA 16802
AU: Yannuzi, V
EM: vty100@psu.edu
AF: Department of Meteorology Pennsylvania State University, 503 Walker Building, University Park, PA 16802
AU: Prenni, A
EM: prenni@lamar.colostate.edu
AF: Department of Atmospheric Sciences Colorado State Univesrity, Colorado State University, Fort Collins, CO 80523
AU: DeMott, P
EM: pdemott@lamar.colostate.edu
AF: Department of Atmospheric Sciences Colorado State Univesrity, Colorado State University, Fort Collins, CO 80523
AB: Mixed-phase arctic stratus clouds are the predominant cloud type in the Arctic . Perhaps one of the most intriguing of their features is that they tend to have liquid tops that precipitate ice. Despite the fact that this situation is colloidally unstable, these cloud systems are quite long lived - from a few days to over a couple of weeks. Previous studies have suggested that this longevity may be due to a paucity of ice nucleating aerosols (ice nuclei, or IN) in the arctic. Such studies have shown that small changes in IN concentrations can cause large changes in the amount of liquid water within a mixed-phase stratus deck. We use the Regional Atmospheric Modeling System (RAMS) to simulate the time period of October 9-11 from the Mixed-Phase Arctic Cloud Experiment (M-PACE) which was conducted in October of 2004. During this period the North Slope of Alaska and Arctic Ocean were covered by an extensive mixed-phase straus deck. Using heterogeneous ice nucleation parameterizations typical of most models (e.g. Meyers et al., (1992)), the simulated clouds rapidly glaciate. Unlike the observed clouds, very little liquid remains and most of the region is covered by thin ice clouds in the simulations. Measurements during M-PACE suggest that the IN concentrations predicted by typical parameterizations are, perhaps, an order of magnitude too large for the Arctic. Using data taken during M-PACE, the existing IN parameterizations in RAMS were modified. Simulations using the new parameterizations illustrate that arctic mixed-phase clouds can maintain large amounts of liquid water because of the following: (1) IN concentrations are particularly low in the Arctic, leading to a weak glaciation process. (2) Cloud processing of IN, whereby ice nucleation removes IN from the pool of available nuclei, effectively reduces IN concentrations leading to larger liquid amounts. (3) If IN concentrations are too large, cloud
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0320 Cloud physics and chemistry
DE: 0321 Cloud/radiation interaction
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005