An ISDAC case for LES intercomparison: model setup and preliminary results

Description

In this presentation, we will describe a new intercomparison based on a shallow stratus cloud observed over the sea ice during Flight 31 of the Indirect and Semi-Direct Aerosol Campaign (ISDAC). The intercomparison is designed to investigate the origins for the diversity among large-eddy simulation results documented in previous studies of mixed-phase clouds. This study expands earlier work in two principal ways: through unification of some previously unconstrained aspects of models and via analysis of previously unexamined relationships among microphysics, radiation, and cloud dynamics. Specifically, mass-size and fall speed-size relationships are prescribed, so that the rates for depositional growth and sedimentation are constrained across different models. A simple parameterization for the longwave radiative cooling rate is also formulated to eliminate another potentially important source of inter-model variability. Preliminary results from simulations demonstrating the effect of increased ice number concentration on cloud structure will be presented.