A coupled land-surface large-eddy simulation model for nocturnal boundary layer studies

Accurately reproducing the dynamic two-way interaction between the land surface and the atmosphere in the stable boundary layer (SBL) requires detailed treatment of the governing physical processes. Increasingly, large-eddy simulation (LES) is used for this purpose. In these studies, the dominant treatment of surface boundary conditions is to specify a known state or flux. This results in one-way or weak two-way coupling between the land surface and the boundary layer. Here, LES that is fully coupled to a land-surface model (LSM) is used to investigate the SBL and early morning transitional period. The LSM explicitly solves for the transport of heat and water in a one-dimensional column of the upper soil. Coupling to the atmosphere is achieved through a surface budget that partitions the available radiative forcing into ground heat flux and sensible and latent heat fluxes. The fully coupled model is used to simulate the GABLS3 LES intercomparison case. Turbulent boundary layer profiles and surface fluxes are compared to field data and results from simulations using the original GABLS3 LES intercomparison case boundary conditions (prescribed temperature and moisture state). Overall, simulations with both types of boundary conditions compare well with the general trends observed in the field data for surface fluxes and boundary layer turbulence statistical profiles with some minor differences. The LES-LSM model under predicts the latent heat flux during the night and surface fluxes from LES-LSM simulations do not exhibit the same piecewise behavior during transitional periods observed in simulations that use the GABLS3 LES intercomparison boundary conditions. In addition to basic comparisons with field data and the GABLS3 boundary conditions, the LES-LSM simulations are also examined for sensitivity to land surface and soil parameters.