Modeling and observations of clouds, convection, and the boundary layer

Steve Krueger & Pete Bogenschutz
University of Utah


Cloud-resolving models resolve many cloud processes, including deep convection, that are subgrid-scale in NWP models, and therefore can serve as benchmarks for evaluating cloud and convection parameterizations in NWP models. Cloud-resolving models can also be used to develop closures for cloud and convection parameterizations, and to answer questions about the validity and generality of currently used closures. Several potential applications will be described.

Very-fine-grid cloud-resolving models that resolve the large turbulent eddies in the boundary layer and in clouds can be used to develop and test improved subgrid-scale cloud parameterizations for coarse-grid explicit-convection models. We are doing this using the assumed probability density function (PDF) method. We will present the basis of this method, as well as an evaluation for a variety of cloud regimes and grid sizes ranging from 1 km to 100 km, with an emphasis on grid spacings around 4 km.

A new opportunity is to use results from global climate models that have replaced their conventional cloud and convection parameterizations with embedded 2D cloud-resolving models (multiscale modeling framework, or MMF). The MMF allows cloud-resolving models to interact with large-scale dynamics, something that stand-alone cloud-resolving models cannot do. The MMF appears to better represent certain phenomena, such as the MJO. Careful analysis of MMF results should provide new insights into such well-represented phenomena.