Collaborative Research: Cloud Macrophysical Parameterization and Its Application to Aerosol Indirect Effects

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This grant will support a collaborative research effort at three universities and three government laboratories to develop a method to represent liquid water clouds in the atmospheric boundary layer (i.e. at levels within about 2km of the surface). The method, which has the acronym CLUBB (clouds unified by binormals), will address the disparity between the size of a climate model grid box (typically 100km) and the much smaller sizes of the updrafts and downdrafts which occur in boundary layer clouds (perhaps 100m). The research will use a variety of observations in concert with simulations from more detailed models (including large-eddy simulation models) to construct joint probability density functions (PDFs) for vertical velocity, temperature, moisture, and hydrometeor species. The PDFs will then be used to simulate the formation of clouds (particularly boundary layer cumulus and stratocumulus clouds) and the extent to which cloud reflectivity and other properties are determined by aerosols. CLUBB will be implemented in two climate models, one at the National Center for Atmospheric Research and one at the NOAA Geophysical Fluid Dynamics Laboratory. The research was proposed in responsee to a solicitation for Climate Process and Modeling Teams (CPTs), which are intended to perform work yielding improvements to climate models over a three-year time period.The results of this CPT project are expected to have broad scientific and practical benefits, since climate models are a basic research tool in climate-related research. Furthermore, climate models are increasingly in demand as tools for decision support by policy makers considering strategies to address climate variability and climate change. Thus, improvements in climate models offer the prospect of better guidance for policy decisions. In addition, the grant will support the education of three graduate students, and for the employment and mentoring of three postdoctoral researchers.