Relationships among the surface wind, horizontal synoptic-scale
pressure gradient and topography are studied in the Willamette Valley
in western Oregon. Terrain features alter the standard surface wind-pressure
gradient relationship such that the angle between the surface
wind and the surface geostrophic wind is most frequently 60°.
In winter the surface flow is predominantly southerly and surface
geostrophic flow varies from southerly to westerly. Little diurnal
change occurs in the average surface wind, the average surface
geostrophic wind and their relationship with each other because the air
in the valley is generally stably stratified throughout the day.
Partially in response to the northward extension of the subtropical
anticyclone summertime surface winds and surface geostrophic
winds are northerly, except during afternoon episodes of
marine air invasion when surface winds are westerly. The pressure
gradient is 88% less intense in summer but the ratio of the magnitudes
of the surface wind and surface geostrophic wind, R, is 125%
greater than in winter. However, a sharp summertime morning
maximum in R of -0.67 is diminished by early afternoon as differential
surface heating establishes a strong afternoon pressure
gradient.
When the surface geostrophic wind vector is cross-valley, the
surface wind is still most frequently parallel to the valley and the
surface geostrophic wind speed is largest and most variable.
Because of the importance of terrain and meso-scale events,
little correlation between the surface winds and synoptic-scale pressure
gradient is found. / Graduation date: 1975
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/29501 |
| Date | 23 October 1974 |
| Creators | Andrews, Leta |
| Contributors | Mahrt, Larry J. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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