A large-eddy simulation study of the impact of different land-atmosphere coupling schemes on the dynamics of the nocturnal boundary layer (Invited)
Abstract
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 many 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. The impact of how this coupling is modeled on atmospheric boundary layer (ABL) dynamics is still not fully understood, especially under transitional and weakly turbulent conditions. Here, LES that is fully coupled to a land-surface model (LSM) is used to investigate the nocturnal and the transitional periods of the diurnal cycle. The LSM explicitly solves for the transport of heat and water in a one-dimensional column of the upper soil and is coupled to the atmosphere through a surface energy budget. The fully coupled LES-LSM is used to simulate the third GEWEX (Global Energy and Water Cycle Experiment) ABL (GABLS3) LES intercomparison case. Turbulent boundary layer profiles and surface fluxes are compared to field data and results from simulations using three different levels of physical description as lower boundary conditions. These include simulations with prescribed temperature and moisture state, with a LSM that uses a bare-soil approximation and a LSM that include a skin layer. Overall, simulations with all three types of boundary conditions compare fairly well with the general trends observed in the field data for surface fluxes and boundary layer turbulence statistical profiles during the intercomparison time period (night to early morning) with a few differences. The LES-LSM model under-predicts the latent heat flux during the night and over-predicts the ground heat and moisture fluxes. The addition of a skin layer improves flux predictions during the night and early morning. Surface fluxes from both types of LES-LSM simulations do not exhibit the same piecewise behavior during transitional periods observed in simulations that use prescribed temperature and moisture states as boundary conditions. This results in a delayed transition from stable to unstable conditions for the early morning time period.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFM.H21J..05S
- Keywords:
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- 1843 HYDROLOGY / Land/atmosphere interactions;
- 3307 ATMOSPHERIC PROCESSES / Boundary layer processes;
- 3379 ATMOSPHERIC PROCESSES / Turbulence