Evaluating Cloud Microphysics in High-Resolution WRF Simulations for Next Generation Climate Models
Wang, Y., Pacific Northwest National Laboratory
General Circulation and Single Column Models/Parameterizations
Figure 1. One-hour snapshot (left panel) and two-hour snapshot (right panel) of missing ratios (units g/kg) for graupel (shades) and cloud ice (contours) from idealized thunderstorm experiments. Contour levels for MP2, MP6 and MP8 (0.01, 0.05, 0.1, 0.2, 0.4).
Figure 2. Cloud fraction comparison from the objective analysis (ARM ARSCL data) and WRF TWP-ICE experiments. On top of cloud fraction (non unit, shading), we also plot the water vapor mixing ratio (units g/kg) in contour levels of 1, 2, 4, 8, and 16.
As “high-performance” computing resources and technology advance, the next generation of climate models is going to be “convective resolving” (less than 10-km resolutions), or so-called “cloud permitting”. At such high spatial and temporal resolutions, the truth gained from traditional single-column model performance may be INVALID. Because convective processes are not parameterized as in current generation climate models, the detailed cloud microphysics becomes one of the key parameterizations that play the most significant role in next generation climate models. Therefore, the evaluation of those cloud microphysical parameterizations becomes urgently needed and critically important to the success of the next generation of climate models in order to ensure VALID future projections of climate changes.
Our preliminary evaluations using a 2-D idealized thunderstorm simulation (250-m resolution) illustrate the wide discrepancy of the “ice-phase” cloud microphysics (Fig. 1) because other physical parameterizations and interactions were turned off. The TWP-ICE simulations (4-km resolution) again confirm that the “ice-phase” parameterization of cloud microphysics contributes most to the wide discrepancy between models and observations (Fig. 2). To further illustrate the potential influence of the cloud-radiation feedback, we have carried out another set of model evaluations, in which the interactions between cloud and radiation parameterizations (both longwave and shortwave) have been turned off. Our findings highlight the importance of “ice-phase” cloud parameterization, while the interactions between cloud and radiation plays a secondary, non-negligible role in contributing to the wide discrepancy (figures not shown).
Wang Y, CN Long, LR Leung, J Dudhia, SA McFarlane, JH Mather, SJ Ghan, and X Liu. 2009. "Evaluating regional cloud-permitting simulations of the WRF model for the Tropical Warm Pool International Cloud Experiment (TWP-ICE, Darwin, 2006)." Journal of Geophysical Research-Atmosphere, 114, in press, doi:10.1029/2009JD012729.