4.16
Modeling the Stable Atmospheric Boundary Layer with a Third-order Closure Model
Anning Cheng, NASA, Hampton, VA; and K. M. Xu
A single-column third order closure model is used to simulate the Global Energy and Water Cycle Experiment (GEWEX) Atmospheric Boundary Layer Study (GABLS) case. The vertical profiles of the horizontal velocity, and the variances of the three-dimensional velocity and potential temperature are compared with those produced by a 1.5-order closure single-column model. The high-moment equations require a much shorter time step than that used by the 1.5-order closure model. The results are also sensitive to the dissipation length scale and the surface boundary conditions. From the third-order closure model, we find that the horizontal components and
of turbulent kinetic energy (TKE) are much larger than the vertical component
, which is consistent with results from large eddy simulations. This is because the shear production term is large in the
and
equations while it is very small in the
equation. Also, the buoyancy production of
is negative. However, the 1.5-order closure model cannot predict this anisotropy in the TKE. Also, third-order closure models that only predict the vertical velocity variance
is assumed in such models cannot simulate the stable boundary layer well, since the TKE calculated by these models is too small.
Session 4, boundary layers: stable, and convective, and transitional (Parallel with Sessions 5 and 6)
Tuesday, 10 August 2004, 8:00 AM-5:15 PM, Vermont Room
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