The numerical modeling of motions in the atmosphere's
planetary boundary layer (PBL) is a challenging task. In
general, the boundary layer interacts with both the overlying
atmosphere and the underlying land or water surface
in a complex manner. Random turbulence is also present in
the PBL which precludes exact prediction by numerical
models. Nonetheless, expensive three-dimensional numerical
models have been developed which, with several parameterizations
and assumptions, can give a good idea of the PBL
structure in many situations. However, on certain occasions,
there is strong mixing evident in the PBL which may
enable one to describe the structure of the boundary layer
in a much-simplified theoretical model. By eliminating
the vertical dimension from consideration, this two-dimensional
mixed-layer model can be applied to mesoscale phenomena
(horizontal length scale < 100 km) at greatly-reduced
costs.
The equations for motion and mixed-layer height are
derived for such a situation and methods appropriate to the
numerical modeling of the atmospheric mixed layer are discussed.
Using an energy-conserving finite-difference
analog of the model equations, the model is integrated in
time to simulate the motions which were associated with the
atmospheric vortex street observed near Cheju-do, South
Korea on 17 February 1975. Experiments were carried out
which investigated the effects of lateral diffusion, horizontal
resolution, and mixed-layer depth.
It is concluded that, given proper representation of
prognostic variables on a staggered finite-difference grid,
only small, realistic values of eddy diffusivity need be
utilized. It also appears evident from the numerical experiments
and atmospheric observations that the vortex
street will form only when the obstacle which triggers its
formation protrudes above the mixed layer. Although the
wind fields in the simulations sometimes lack clear, fully
rotational cells well downstream of the island, the characteristic
sinusoidal pattern observed in laboratory experiments
and cloud photographs is explicitly resolved by
the model. The simulated vortex street also compares favorably
with the observed in that the dimensionless governing
parameters of the simulated vortex street (the Reynolds
number, Strouhal number, Lin's parameter, the spacing
ratio, and the speed ratio) closely match the observed
values. / Graduation date: 1981
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/28930 |
| Date | 20 March 1981 |
| Creators | Ruscher, Paul Harold |
| Contributors | Deardorff, James W. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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