Evaluation of Cloud Properties and Precipitation for Stratiform and Convective Simulations
U.S. Department of Energy (DOE) researchers continue to test the performance of model cloud microphysics, or the way droplets and ice crystals form, evolve, and precipitate in models. Microphysics parameters influence cloud evolution and climate conditions and the complex schemes require extensive and ongoing testing against observations. Simulations of frontal stratiform precipitation events are sensitive to the representation of snow in the cloud microphysics parameterization, while convective precipitation events are mainly sensitive to the representation of the largest rimed (ice-coated) ice species, either graupel (cold ice-water condensed on a snow crystal) or hail (ball of dense layered ice). DOE scientists at Brookhaven National Laboratory and their collaborators performed model microphysics sensitivity experiments of the representation of snow and rimed ice species for two composites of 15 stratiform and 15 convective observed precipitation events. Cloud properties and surface precipitation characteristics of all events were rigorously evaluated against satellite- and radar-derived observations. Simulations that include graupel and a temperature-dependent snow parameter during both convective and stratiform events yielded results that consistently agreed better with satellite observations. The enhanced ice depositional growth rates in these experiments led to significantly improved cloud-top heights. Compared to previous model experiments, surface precipitation was less sensitive to whether graupel or hail was chosen as the rimed ice species. However, capturing peak precipitation rates required including graupel in the microphysics scheme. This study used precipitation and cloud observations to constrain and improve the requirements for cloud microphysical schemes for both convective and stratiform cloud modeling.
Van Weverberg, K., N. van Lipzig, L. Delobbe, and A. Vogelmann. 2012: “The Role of Precipitation Size Distributions in Km-Scale NWP Simulations of Intense Precipitation: Evaluation of Cloud Properties and Surface Precipitation,” Quarterly Journal of the Royal Meteorological Society 138, 2163-81. DOI: DOI:10.1002/qj.1933.