A global, multi-level, wave-mean flow model based on an
approximate version of the primitive equations is developed to
investigate the development of a baroclinic wave field initially
confined to a single zonal wavenumber. The effects of physical
processes (surface drag and thermal damping) and internal diffusion
on the evolution have been examined. The nature of the mean flow
adjustment by the nonlinear baroclinic waves is also studied.
For a simulation with a relatively strong internal diffusion it is
found that a single life cycle characterized by baroclinic growth and
barotropic decay is obtained (as in Simmons and Hoskins, 1978),
whereas with weaker diffusion the wave undergoes secondary life
cycles before a nearly wave-free state is reached (as in Barnes and
Young, 1991). In an experiment with weak 4th order diffusion
secondary life cycles occur with little net decay. Relatively strong
barotropic growth follows the initial life cycle.
In experiments with surface drag (Rayleigh friction) and thermal
damping (Newtonian cooling), repeated life cycles of baroclinic
growth and barotropic decay can be obtained. It is found that in the
complete absence of surface drag, the flow evolves to a nearly
wave-free state after one secondary cycle. This demonstrates that
surface drag plays an important role in nonlinear baroclinic
instability. With relatively strong surface drag multiple life cycle
behavior is found for sufficiently strong thermal damping. Such a
behavior strengthens for very strong thermal damping. A steady
wave state in which the wave amplitude equilibrates at an
essentially constant level has only been obtained with very strong
"potential vorticity damping".
Both the "barotropic governor" process (James and Gray, 1986)
and the baroclinic adjusment process are responsible for major
parts of the stabilization of the mean flow in simulations with and
without surface drag and thermal damping. However, the "barotropic
governor" process dominates the flow evolution in the model
simulations without surface drag and thermal damping. The
"barotropic governor" modifies the meridional gradient of zonal
mean potential vorticity, which influences the baroclinic
adjustment. / Graduation date: 1992
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/28777 |
| Date | 11 June 1991 |
| Creators | Wang, Chunzai |
| Contributors | Barnes, Jeffrey R. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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