A virtual cloud physics laboratory

Abstract The representation of clouds in weather and climate models is hampered by limited understanding of small-scale cloud processes, including how cloud and precipitation particles interact with cloud turbulence. Observations of natural clouds provide direct information only on cloud properties and not processes, and it is difficult to isolate impacts of specific processes on the evolution of cloud properties. Significant progress has been made through recent laboratory cloud chamber studies in understanding the roles of cloud processes. However, it is not straightforward to bridge laboratory observations (at scales of microns to meters) with natural cloud observations (encompassing a much wider range of scales) and weather and climate models that typically have resolutions no finer than ∼1 km. With advances in computing power, high-resolution cloud modeling holds considerable promise to bridge these scales. Using advanced microphysics schemes that track representative cloud and precipitation particles combined with targeted observations of laboratory or natural clouds, high-resolution models can serve as a “virtual laboratory” for studies of cloud processes across scales. Two examples are presented herein: 1) direct-numerical simulations (∼1.7 mm grid spacing) of a laboratory cloud chamber and 2) high-resolution (7.5 m grid spacing) large-eddy simulations of an observed precipitating cumulus cloud. We highlight the potential of this approach to address long standing problems in cloud physics, including how drop size distributions evolve in turbulent clouds, and how the approach can provide data for improving bulk cloud microphysics schemes in weather and climate models.