Evaluation of New Monin–Obukhov and Bulk Richardson Parameterizations of the Surface Layer in Large Eddy Simulations

In numerical weather prediction models, surface-layer parameterizations are needed to couple the land surface to the first model level of the atmosphere, which is typically ~10s of meters above the surface. Traditionally, Monin-Obukhov Similarity Theory (MOST) has been used to parameterize the land-atmosphere exchange. There are many different ways to represent the functional form of the MOST equations, which can be derived based on observations. A different approach is to parameterize the surface layer using a Richardson number (R_ib) formulation. During August 2017, the Land-Atmosphere Feedback Experiment (LAFE) was conducted over northern Oklahoma with the goals of improving the understanding of the land surface on the exchange of heat and momentum through the lower atmosphere. Using observations from three flux towers installed by ATDD, new formulations of MOST and R_ib were developed. These new formulations were then implemented into the Collaborative Model for Multiscale Atmospheric Simulation (COMMAS) Large Eddy Simulation model and the results compared to the observations. Several case studies were run from both from LAFE and from the Verifications of the Origins of Rotation in Tornadoes Experiment (VORTEX-SE) Although there were improvements in using the new MOST formulations, the largest improvements were in using a R_ib formulations of the surface-layer parameterizations. These results motivate the need to consider transitioning to using a R_ib approach to surface-layer parameterizations in operational numerical weather prediction models.