Investigating the convergence of boundary layer properties as a function of grid spacing within WRF-LES
Rutt, Kaitlin A.
MetadataShow full item record
Large Eddy Simulation (LES) is a numerical technique using a filtering approach of the Navier-Stokes equations. With sufficiently fine grid spacing, LES explicitly resolves the largest, most energy-containing eddies in the Planetary Boundary Layer (PBL) which are responsible for a majority of PBL turbulent transport. This study will specifically look at a clear daytime Convective Boundary Layer (CBL) using the weather research and forecasting model for large-eddy simulations (WRF-LES). A variety of grid spacings are used ranging from 12.5 to 150 meters in the both the horizontal and vertical. Three cases represent the data with an aspect ratio of 1, constant vertical grid spacing of 12.5 meters, and constant horizontal grid spacing of 100 meters. The grid resolution of convergence is defined through analysis of CBL characteristics from 11AM to 3PM for a single day. Looking into the mean, variance, and turbulent kinetic energy (TKE) of the CBL, results show the best grid spacing for each statistic varies with the variable of interest. Further emphasis will be placed on the two-dimensional energy spectrum with respect to model resolution to aid in determining future LES modeling capabilities. Overall, convergence is found the most in case 3 (constant horizontal grid spacing of 100 meters), which indicates very little dependence in the vertical grid spacing. Some of the statistics reveal similarities in the magnitudes between cases 1 and 2, which leads to the result that finer resolution in the vertical may not always be necessary. The conclusions made in this study may vary with a different PBL setup and model.