Improved Parameterization of Microphysical and Optical Properties of Clouds in Global Climate Models

The overall objective of the proposed work is to study the interaction of radiation with MPCs to deduce relations between the atmospheric thermodynamic state, as given by resolved model variables (such as temperature, humidity, and winds), and cloud microphysical processes (condensation/evaporation and deposition/sublimation) in the mixed-phase regime. To that end, we will combine our knowledge of light scattering by non-spherical particles and atmospheric radiative transfer with expertise in cloud parameterisation. To implement and test the deduced relations we will use a limited-area, high-resolution cloud-resolving model (CRM), e.g. the fifth-generation Mesoscale Model (MM5) (Dudhia 1989, Grell et al. 1994). This model has recently been modified for use in polar regions (referred to as Polar MM5, http://www-bprc.mps.ohio-state.edu/PolarMet/pmm5.html). The advantage of using this type of model is that we can assume that the resulting condensation/deposition fills the whole grid box volume, so that consideration of fractional cloudiness may be ignored. We expect that the resulting parameterisations of microphysical properties as well as MPC radiation properties will be suitable for inclusion in GCMs.

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