Single-column modeling of Arctic stratiform clouds: Development and evaluation of bulk microphysics parameterizations.

摘要

Previous studies have indicated that climate models utilizing bulk microphysics parameterizations often poorly simulate Arctic stratiform clouds. To characterize these deficiencies and improve climate simulations, a single-moment microphysics scheme is carefully evaluated against observations and a new double-moment scheme is developed. These parameterizations are tested using the single-column modeling strategy. Observed and retrieved cloud properties were obtained during the 1997–1998 Surface Heat Budget of the Arctic Ocean experiment (SHEBA) and the First ISCCP Regional Clouds Experiment - Arctic Clouds Experiment (FIRE-ACE).; In single-column models, advective and dynamic forcing must be specified. A new method is described that constrains temperature and water vapor advection profiles obtained from the European Centre for Medium Range Weather Forecasts (ECMWF) to observed heat and moisture budgets. By constraining the advective forcing, uncertainty in evaluating the microphysics parameterizations is reduced. This constrained advection data set is used to force the single-column model simulations detailed in the paper.; A single-moment microphysics parameterization currently utilized by several climate models is found to be inadequate for modeling Arctic clouds mostly due to deficiencies in simulating the cloud phase and LWP (which are crucial for correctly predicting the surface radiative fluxes). These biases are attributed to deficiencies in simulating the glaciation of supercooled liquid water and uncertainties in the ice crystal number concentration. A new double-moment microphysics scheme is developed to address these shortcomings. The new scheme incorporates several physically-based parameterizations that allow for an explicit treatment of interactions between the cloud microphysics, aerosol, and thermodynamics. It simulates reasonably well three cloud systems observed during SHEBA/FIRE-ACE and substantially improves the simulation of a mixed-phase stratus relative to the simpler single-moment scheme. The new scheme may be used in mesoscale or cloud resolving models; a simpler version of the scheme may be developed for global climate models.