HR: 0800h
AN: A21E-0765    [Abstracts]
TI: Towards a realistic deposition coefficient expression for cirrus cloud modeling
AU: * Nelson, J T
EM: jnelson@se.ritsumei.ac.jp
AF: Ritsumeikan University, 1-1-1 Nojihigashi, Kusatsu, 525 8577, Japan
AU: Kay, J E
EM: jenkay@ucar.edu
AF: National Center for Atmospheric Research, 1850 Table Mesa Drive, Boulder, CO 80305, United States
AB: Ice crystal deposition (condensation) coefficients affect ice crystal shape and size, two parameters that are important for cloud processes and cloud radiative impacts. Moreover, due to their effect on crystal mass uptake, deposition coefficients affect both the supersaturation at the crystal surface and the ambient supersaturation in the cloud. However, deposition coefficients are sensitive to the surface supersaturation (a fact that is widely ignored), which makes it difficult to use realistic deposition coefficient values in cloud models. The goal of our work is to find a realistic expression for the ice deposition coefficient that can be easily inserted into existing cloud models. For simplicity, we assume that only one coefficient applies to the entire surface, an assumption that gives a reasonable approximation for spherical and isometric crystal shapes. After relating the surface supersaturation to the ambient supersaturation, we determine a general expression for the deposition coefficient as a function of the ambient supersaturation and ice crystal size. Using an adiabatic parcel model with binned microphysics (Kay et al., 2006), we demonstrate the influence of a realistic deposition coefficient on ice crystal nucleation and growth.Finally, we assess if a more realistic deposition coefficient can help explain recent observations of high ice supersaturation in cirrus.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0320 Cloud physics and chemistry
DE: 3311 Clouds and aerosols
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting