Coastal-Trapped and Frontal-Trapped Waves in a Continuously Stratified Western Boundary Current - A Contribution to the Gulf Stream Meanders Experiment

Coastal-Trapped and Frontal-Trapped Waves in a Continuously Stratified Western Boundary Current - A Contribution to the Gulf Stream Meanders Experiment
Author: Mark E. Luther
Publisher:
Total Pages: 85
Release: 1980
Genre:
ISBN:

The effects of a realistic western boundary current on the alongshore propagation of sub-initial waves trapped by a sloping bottom topography are studied using a numerical model incorporating realistic bottom topography and a current field which is in thermal wind balance with the density field. This models the Gulf Stream as it flows along the continental slope off North Carolina. The mean state velocity and density fields do not vary alongshore and are continuous in the horizontal as well as the vertical. The linearized, inviscid equations of motion for small amplitude disturbances yield a single governing equation for the perturbation pressure. This equation is solved using a marching method for elliptical problems. The dispersion relations are obtained by searching for the resonance response of the system to an arbitrary uniform forcing term. Four discrete stable modes of Rossby-like waves are identified, all propagating in the upstream direction. A mode-coupling resonance is found between the first two modes. For small wavenumber, the first mode is trapped within the frontal zone on the cyclonic side of the mean current with a smaller barotropic component over the shelf. This 'frontal trapping' is due to the quasi-geostrophic potential vorticity gradient in the mean current. For larger wavenumber, the first mode becomes primarily a barotropic shelf wave. The second mode is a purely barotropic shelf wave for small wavenumbers, but becomes a frontal-trapped wave at large wavenumbers. For the higher wave modes, most of the energy is trapped near the surface in the frontal zone. (Author).

On Coastal Trapped Waves at Low Latitudes in a Stratified Ocean

On Coastal Trapped Waves at Low Latitudes in a Stratified Ocean
Author: Richard Dennis Romea
Publisher:
Total Pages: 506
Release: 1982
Genre: Ocean waves
ISBN:

The response on the continental shelf of a baroclinic ocean to driving by an alongshore coastal wind stress and by barotropic and baroclinic wind forced interior motions is studied as a function of latitude. The relative excitation of continental shelf waves and internal Kelvin waves is studied. The response of a rotating stratified ocean with a vertical boundary, forced at the surface by an alongshore coastal wind stress, shows vertically propagating subinertial motions. Several examples which illustrate the basic properties of the response are presented. Changes in amplitude and frequency with depth are predicted. Components that decay with depth from the surface and components that represent coastal internal Kelvin waves with negative vertical group velocity and upward phase propagation are forced. The effect of bottom Ekman layer friction and slope topography on free internal Kelvin waves is examined, using both a steep and weak slope model. The steep slope represents the low latitude case while the weak slope represents the mid-latitude case. There are substantial differences between the results from the two models. Free waves are frictionally damped and offshore and vertical phase shifts are induced by friction, as well as an onshore flow. Topography induces changes to the wave frequency and alongshore phase speed. The modal amplitude is altered and an onshore flow is induced. Sea level and current velocity data from the equator to 17°S on the west coast of South America show that low frequency (0.1-0.2 cpd) fluctuations propagate poleward with phase speeds similar to those predicted for first mode baroclinic Kelvin waves. The sea level and currents are coherent and approximately 1800 out of phase. The waves do not appear to be the result of local atmospheric forcing. Empirical orthogonal functions show that the alongshore and vertical structure of alongshore velocity is consistent with first mode internal Kelvin waves.

Particle Flux in the Western Black Sea in the Present and Over the Last 5000 Years : Temporal Variability, Sources, Transport Mechanisms

Particle Flux in the Western Black Sea in the Present and Over the Last 5000 Years : Temporal Variability, Sources, Transport Mechanisms
Author: Bernward J. Hay
Publisher:
Total Pages: 612
Release: 1987
Genre: Black Sea
ISBN:

The particle flux in the present and over the last 5,000 years was investigated in the Black Sea in a comparative study with samples from time-series sediment traps and laminated core sediments. The sediment trap samples were collected in the southwestern Black Sea over 2 1/2 years at sampling intervals of about two weeks. Sediment core samples were derived from the central part of the western Black Sea, deposited throughout the last 5,000 years during which the Black Sea was anoxic. Conclusions from this study shed important light on temporal and regional variability of the particle flux in the Black Sea, dominant particle sources, and particle transport mechanisms. Dominant particle sources are biogenic matter (coccolithophorids of the species Emiliania huxleyi, diatoms, and silicoflagellates) and terrigenous matter from the Danube and nearby local rivers. The relative importance in the supply of these particles varies annually and can be grouped into three phases: Phase I (June-October) coccolithophorid production, Phase II (November-January) - resuspension of coccoliths and terrigenous matter, and Phase III (February-May) river input of terrigenous matter and production of diatoms and silicoflagellates. Once removed from the surface water, particles settle rapidly at a rate of 115 ±70 m/day. Regionally, the particle flux varies considerably. Throughout the last 1,000 years (sediment unit I), the particle flux (paleoflux) was more than 5 times larger in the central part of the western Black Sea than at present in the southwestern Black Sea, mostly because of the 11 times larger supply of coccoliths. The coccoliths were probably largely produced on or adjacent to the Danube shelf in the northwestern Black Sea and subsequently resuspended and transported offshelf by the fall storms. Terrigenous matter in the central part of the western Black Sea is higher by a factor of 3 compared to the southwestern Black Sea. The coccoliths are concentrated in the white laminae (>93 % CaCO3), and if the seasonal dynamics in the particle supply at the sediment trap site is taken as a standard, the white laminae would be deposited between about June and January. The black laminae contain largely terrigenous matter and form during the peak river discharge period between about February and May. Compared to the last 1,000 years (unit I), the particle flux in the central part of the western Black Sea between 1,000 and 5,000 years B.P. was smaller by a factor of three, because the salinity was still too low during this time period for the coccolithophorid Emiliania huxleyi to exist. The Black Sea was a fresh water environment before more than 5,000 years ago and gradually became brackish; Emiliania huxleyi became established after the salinity exceeded 11%. The terrigenous matter supply remained about constant over the last 5,000 years. The western Black Sea is dominated by terrigenous input from the Danube as revealed by the illite/montmorillonite ratio. Seasonally, the terrigenous matter from the Danube appears to be traceable in the southwestern Black Sea, as seen by the Ti/Al and illite/montmorillonite ratios in the sediment trap samples.

Stratified Coastal Trapped Waves and Mean Flows

Stratified Coastal Trapped Waves and Mean Flows
Author:
Publisher:
Total Pages: 4
Release: 1998
Genre:
ISBN:

Our long term goals are to identify the roles that rectified subinertial waves and mesoscale motions play in the mean-flow transport of fluid properties in the coastal ocean and to apply these ideas to cross-margin transport of physical, chemical, and biological properties. In addition, we are interested in the interaction and relative effect of wave-driven transport verses frictionally driven boundary layer transport. Coastal waves and wave-generated mean flows are studied in a stratified, rotating model ocean. Waves trapped to the coast are generated by time-dependent flow over a sloping and irregular bottom. In this study, we will study the rectified flow resulting from oscillatory forcing over a sloping bottom, both with and without additional ridges, and with and without stratification. Short-term goals of this study include quantifying the evolution of the vertical structure of the along-slope mean flow driven by non-linear interactions of the coastal trapped wave and damped by friction. The effects of stratification on the cross-slope overturning circulation will be examined to evaluate the strength of wave-driven mean flow verses frictionally driven flow.

Physical Oceanography of Continental Shelves

Physical Oceanography of Continental Shelves
Author: K.H. Brink
Publisher: Princeton University Press
Total Pages: 272
Release: 2023-09-12
Genre: Science
ISBN: 0691236453

"This book is intended as a graduate-level textbook and professional reference on the physical oceanography of the continental shelf and slope. Defined as water deeper than about three meters and shallower than a kilometer, this region of the ocean is important for a variety of scientific and practical reasons, from its high biological productivity and role in distributing outflows from the continents to its heavy usage in transportation and recreation. In recent years, research on the coastal ocean has expanded as the study of both short- and long-term anthropogenic change has become increasingly urgent. Yet there is no comprehensive treatment of the dynamics of this critical region. The book covers a range of topics involving currents and water properties, including turbulent boundary layers, wind driving, tides, buoyancy currents, waves, instabilities, and connections with the open, deep ocean. Brink's approach-informed by over a decade teaching the corresponding course in Woods Hole/MIT's joint program-centers on the dynamics of particular processes and combinations of processes, but also includes copious observational examples. Intended to be accessible to graduate students in a range of oceanographic specialties, the book assumes 2-3 years of university-level math and at least an introductory course in quantitative physical oceanography"--