The perturbation of a stably-stratified flow by irregular
terrain is studied utilizing a seven-layer, hydrostatic, and
potential enstrophy and energy conserving primitive equation
model. The Island of Oahu, Hawaii, and the surrounding ocean area
of 130 km x 100 km is chosen as the model topography. The domain is
covered with a 5 km x 5 km mesh of 26 x 20 grid points in the
horizontal. A cyclic boundary condition is imposed at the lateral
boundaries. In order to give finer resolution to the lower
atmosphere, an irregularly spaced sigma-coordinate is used in the
vertical. Uniform east-north-easterly large-scale geostrophic
winds up to the 400 mb level are imposed in order to represent the
typical trade-wind condition.
The pressure perturbation related to the mass flux divergence
associated with the terrain irregularities, and the land-sea
temperature difference associated with the different responses to
the insolation during the daytime, are found to play a key role in
determining the velocity field in the horizontal as well as in the
vertical. Asymmetric surface pressure arises, due to the
topographically induced vertical motion, with high pressure at the
windward slope and low pressure at the downwind slope of the
island.
Daytime heating of the island induces low pressure on the
island surface. This effect is the most significant at the lee
side and inland portion of the island where the effect of cold-air
advection from the ocean is minimal. At the lee side of the
island the negative pressure perturbation induced by the daytime
heating favors the establishment of a reverse flow toward the
island, but the mountain range at the lee side of the island and
prevailing tradewind prevent this low-level inflow from
penetrating further inland. At the upwind side of the island, the
flow field is mostly determined by topographic slope rather than
by the heating of the island surface.
The perturbation to the basic flow decreases rapidly upward.
But a vertical cross-section of the horizontal divergence and the
vertical velocity fields shows well defined wave motions up to the
domain top level. The wave motions also appear downstream and
upstream of the island with reduced amplitudes away from the
island. These suggest the existence of hydrostatic mountain waves
forced by the island contour, as was predicted by previous linear
studies. The windward tilt of the wave axis shows upward
propagation of wave energy, but the wave momentum flux was
negligible. / Graduation date: 1987
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/28920 |
| Date | 09 May 1986 |
| Creators | Kim, Jinwon |
| Contributors | Deardorff, James W. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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