Record Details
Tidal-band and high-frequency internal variability on the central Oregon inner shelf
ScholarsArchive at Oregon State University
| Field | Value |
|---|---|
| Title | Tidal-band and high-frequency internal variability on the central Oregon inner shelf |
| Names |
Suanda, Sutara H.
(creator) Barth, John A. (advisor) |
| Date Issued | 2014-01-29 (iso8601) |
| Note | Graduation date: 2014 |
| Abstract | Analogous to ocean surface waves, waves in the ocean interior also experience steepening, breaking, and dissipation as they approach the coastline. Much less is known about this internal beach. In this work, extensive moored Acoustic Doppler Current Profiler and temperature/salinity data together with optical remote sensing are combined to describe and understand tidal-band and high-frequency internal wave propagation over the Oregon mid and inner shelf. Semidiurnal baroclinic velocity is dominated by the first mode at all locations, with larger velocities on the mid shelf and northern part of a large submarine bank. Mid-shelf sites have baroclinic ellipticity that is near the theoretical value for single, progressive internal tidal waves compared to more linearly polarized currents over the inner shelf. Temporal variability does not correspond to the spring-neap cycle and is overall uncorrelated between mooring locations due to variable along-shelf topography and stratification. An idealized model of two amplitude-modulated internal waves propagating from different directions reproduces some of the observed variability in inner-shelf semidiurnal ellipse parameters. Moored observations were combined with sea-surface imagery to describe the propagation of 11 bore-like internal waves across the inner shelf. The surface expression of these waves is identified by regions of increased pixel intensity during wind speeds between 2 - 5 m/s⁻¹. Optical measurements show that internal waves are refracted by bathymetry, and measured wave speed (~0.15 m/s) is higher than predicted by linear theory (< 0.1 m/s⁻¹). The number and strength of these high-frequency (15 minute period), highly nonlinear features are linked to regional-scale upwelling/downwelling as well as the phase of the mid-shelf internal tide. In general, both surface and bottom-trapped bores are observed on the inner shelf and their polarity can be predicted by the weakly nonlinear parameter of the Korteweg-de Vries wave propagation equation. These bores have different consequences for the amount of horizontal transport they accomplish and where in the water column this transport occurs. The transformation of the internal tide impacts the form of the nonlinear high-frequency oscillations observed on the inner shelf. The most efficient onshore transport of sub-thermocline water is observed during a shallow mid-shelf pycnocline with large mid-shelf semidiurnal displacement that results in only elevation waves onshore. |
| Genre | Thesis/Dissertation |
| Access Condition | http://creativecommons.org/licenses/by/3.0/us/ |
| Topic | Internal Waves |
| Identifier | http://hdl.handle.net/1957/45860 |
