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Large eddy simulations (LESs) provide an attractive way of developing parameterizations for large-scale models such as global climate and weather forecast models. This is because they provide 4-D information which can potentially be used to compute fluxes with sampling errors that are much smaller than those made from in situ measurements. LESs, however, are only viable if we have confidence in their solutions. In particular, high resolution 4-D measurements are needed to test the LESs ability to accurately simulate the organization of convection such as linear and cellular boundary layer circulations. The objective of our research is to demonstrate the usefulness of volume imaging lidar data in LES validation.

To do this, we deployed the University of Wisconsin Volume Imaging Lidar (UW-VIL) at a site on the western edge of Lake Michigan and observed the growth of the convective boundary layer (CBL) over the water during cold-air outbreaks. We also ran the University of Wisconsin nonhydrostatic modeling system (UW-NMS) with microscale grid spacing to simulate lake-induced CBLs. This nonhomogeneous environment offers the advantages of a wide range of CBL depths and convective organization patterns within a simulation domain and requires substantially less computer time when compared to homogeneous CBL simulations that must be run for a large part of the diurnal cycle before several large-eddy turn-overs are obtained.

Previous work using VIL data to validate LES can be found in Avissar et al. 1998.

Ed Eloranta
Tue Nov 16 08:30:34 CST 1999