Atmos. Chem. Phys. Discuss., 9, 14571-14600, 2009
© Author(s) 2009. This work is distributed
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
On the relationship of polar mesospheric cloud ice water content, particle radius and mesospheric temperature and its use in multi-dimensional models
A. W. Merkel1, D. R. Marsh1, A. Gettelman1, and E. J. Jensen2
1National Center for Atmospheric Research, Boulder, Colorado, USA
2NASA Ames Research Center, Moffett Field, California, USA

Abstract. The distribution of ice layers in the polar summer mesosphere (called polar mesospheric clouds or PMCs) is sensitive to background atmospheric conditions and therefore affected by global-scale dynamics. To investigate this coupling it is necessary to simulate the global distribution of PMCs within a 3-dimensional (3-D) model that couples large-scale dynamics with cloud microphysics. However, modeling PMC microphysics within 3-D global chemistry climate models (GCCM) is a challenge due to the high computational cost associated with particle following (Lagrangian) or sectional microphysical calculations. By characterizing the relationship between the PMC radius, ice water content (iwc), and local temperature (T) from an ensemble of simulations from the sectional microphysical model, the Community Aerosol and Radiation Model for Atmospheres (CARMA), we determined that these variables have a fundamental stable relationship that is independent of the cloud time history. For our purposes we use this relationship to provide a bulk parameterization of PMC microphysics to be included into multidimensional models. However, this relationship has the potential to be used in other applications to characterize PMCs. We use a parameterization of the relationship to predict the particle effective radius using only the local temperature and ice water content in a 3-D GCCM for decadal scale PMC simulations. Such a parameterization allows for theoretical ice cloud microphysics to be applied in the GCCM to simulate growth, sublimation and sedimentation of ice particles without keeping track of the time history of each ice particle size or particle size bin. This approach produces realistic PMC simulations including estimates of the optical properties of PMCs. We validate the relationship with PMC data from the Solar Occultation for Ice Experiment (SOFIE).

Citation: Merkel, A. W., Marsh, D. R., Gettelman, A., and Jensen, E. J.: On the relationship of polar mesospheric cloud ice water content, particle radius and mesospheric temperature and its use in multi-dimensional models, Atmos. Chem. Phys. Discuss., 9, 14571-14600, doi:10.5194/acpd-9-14571-2009, 2009.
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