This study investigates wind-driven circulation in the vicinity of the Heceta Bank complex along the Oregon shelf. Numerical experiments forced with steady winds (0.1 Pa) are conducted; upwelling and downwelling cases are compared. The asymmetric bank bathymetry is the only configurational difference from the symmetric bank runs analyzed in Part...
This study examines how coastal banks influence wind-driven circulation along stratified continental shelves. Numerical experiments are conducted for idealized symmetric banks; the standard bank (200 km long and 50 km wide) has dimensions similar to the Heceta Bank complex along the Oregon shelf. Model runs are forced with 10 days...
Observations of oppositely directed, monthly mean alongshore currents and wind stress over the continental margin off the Pacific coast of North America motivate the theoretical examination of mean flow generation by topographic lee-wave drag. We formulate a barotropic model for wind-forced shelf-slope flow over variable topography. Our central objective is...
Two-dimensional, primitive equation model studies of wind-forced flow over a continental shelf Show that, under upwelling conditions, high levels of near-inertial wave energy are found in the interior over the shelf. The regions of elevated wave energy, with maximum wave amplitudes of around ±0.2 m s⁻¹, persist for up to...
The effects of wind-forced upwelling and downwelling on the continental shelf off Duck, North Carolina, are studied through experiments with a two-dimensional numerical primitive equation model. Moored and shipboard measurements obtained during August–November 1994 as part of the Coastal Ocean Processes (CoOP) Inner Shelf Study (ISS) are used for model–data...
As part of a program to improve understanding of the dynamics of the complicated, vigorous eddy and jet flow fields recently observed over the continental shelf and slope, we investigate the potential of intermediate models for use in both process and data assimilation studies of these flows. Intermediate models incorporate...
Motivated by the general objective of pursuing oceanographic process and data assimilation studies of the complex, nonlinear eddy and jet current fields observed over the continental shelf and slope off the west coast of the United States, we investigate the use of intermediate models for that purpose. Intermediate models contain...
The linear stability of a nearly time-periodic, nonlinear, coastal upwelling–downwelling circulation, over alongshore-uniform topography, driven by a time-periodic wind stress is investigated using numerical methods. The near-periodic alongshore-uniform basic flow is obtained by forcing a primitive equation numerical model of coastal ocean circulation with periodic wind stress. Disturbance growth on...
A two-layer model is used to study the properties of free coastal trapped waves which propagate over an idealized continental shelf and continental slope bottom topography. With both stratification and depth variations that are typical of continental shelf and slope regions, barotropic shelf waves and baroclinic internal Kelvin waves axe...
Hourly observations of coastal sea level at stations from Peru to British Columbia are analyzed for low-frequency content. A space-time contour plot of sea level, from four years of data during the 1971–75 period, shows the meridional structure of the seasonal cycle and interannual variability associated with the 1972–73 El...
Several diagnoses of three-dimensional circulation, using density and velocity data from a high-resolution, upper-ocean SeaSoar and acoustic Doppler current profiler (ADCP) survey of a cyclonic jet meander and adjacent cyclonic eddy containing high Rossby number flow, are compared. The Q-vector form of the quasigeostrophic omega equation, two omega equations derived...
An idealized, linear model of the coastal ocean is used to assess the domain of influence of surface type data, in particular how much information such data contain about the ocean state at depth and how such information may be retrieved. The ultimate objective is to assess the feasibility of...
Vertically propagating coastal internal Kelvin waves (IKWs) forward by the alongshore component of the wind at the coast are studied, utilizing an ƒ-plane model of a continuously stratified ocean with a vertical eastern boundary. With an infinitely deep ocean, several initial value problems that illustrate the basic properties of the...
The propagation of incident coastal-trapped waves in the Gulf of California is investigated using a hydrostatic
primitive equation model. The behavior of idealized incident wave disturbances with different amplitudes and
time scales is examined. The incident wave disturbances propagate northward up-gulf along the east side with
no significant change. At...
The effects of alongshore variations in bottom topography on wind-stress-forced barotropic motion over a continental shelf and slope are studied. An idealized channel model with a weakly sloping bottom and with small-amplitude alongshore variations in topography is utilized. Perturbation methods and numerical inversion of Fourier transforms are employed. The effect...
A linearized baroclinic, spectral-in-time tidal inverse model has been developed for assimilation of surface currents from coast-based high-frequency (HF) radars. Representer functions obtained as a part of the generalized inverse solution show that for superinertial flows information from the surface velocity measurements propagates to depth along wave characteristics, allowing internal...
Results from a model of wind-driven circulation are analyzed to study spatial and temporal variability in
the bottom mixed layer (BML) on the mid-Oregon shelf in summer 2001. The model assimilates acoustic
Doppler profiler velocities from two cross-shore lines of moorings 90 km apart to provide improved
accuracy of near-bottom...
Internal tides on the continental shelf can be intermittent as a result of changing hydrographic conditions
associated with wind-driven upwelling. In turn, the internal tide can affect transports associated with upwelling.
To study these processes, simulations in an idealized, alongshore uniform setup are performed utilizing
the hydrostatic Regional Ocean Modeling...
The low-frequency [ω<0.5 cycle per day (cpd)] current fluctuations at four depths in 100 m of waterhave been investigated for two stations on the continental shelf off the coast of Oregon. One station, DB-7,was maintained during the summer of 1972 as part of the Coastal Upwelling Experiment-1 (CUE-I), and theother...
An analysis is presented of the low-frequency fluctuations [ω<0.6 cycle per day (cpd)] of the currents near the Oregon coast, based on the 1972 and 1973 measurements from moored current meters in CUE-1 and CUE-2. Let u and v denote the eastward (approximately onshore) and northward (approximately alongshore) components of...
Along the west Coast of North America, the response of sea level to fluctuations in alongshore wind stress at large alongshore scales (> 1000 km) accounted for a substantial faction of the total sea level variance during summer 1973. Space-time contour plots of sea level and alongshore stress show that...
Sixty-day simulations of flow on the Oregon continental shelf are performed using the Blumberg and Mellor sigma coordinate, primitive equation model. The model is two-dimensional (an across-shelf section) with high spatial resolution and realistic shelf topography. Forcing consists of surface heat flux, either hourly or low-pass filtered wind stress, and...
Case history analysis, cross spectra and multiple regression analysis have been used in a study of low-pass filtered sea level records from the Pacific mainland coast of Mexico in 1971 and 1973–75. During the summer-fall season (May–October), sea level variability is characterized by strong alongshore coherence and nondispersive, poleward phase...
The behavior and relationship of anomalies of monthly mean sea level, coastal sea surface temperature and alongshore wind stress for the eastern Pacific Ocean during the period 1950–74 have been studied. Sea level and temperature records from Yakutat, Alaska (59°N) to Valparaiso, Chile (33°S) and computed alongshore wind stress at...
Observations of the velocity fields over the continental shelf and slope off Oregon and off Peru have shown that there is a phase difference in the onshore-offshore direction, with the velocity fluctuations nearshore leading those offshore in time. It is shown here that the effects of bottom Ekman layer friction...
Time-dependent upwelling on the Oregon continental shelf is studied with a two-dimensional approximation, that is, spatial variations across-shelf and with depth, using the Blumberg–Mellor, finite-difference, stratified, primitive equation model. The time-dependent response of a coastal ocean at rest to constant, upwelling favorable, wind stress is examined. Topography and stratification representative...
The f-plane linear shallow-water equations support coastal Kelvin waves. These waves propagate along the coast and have zero velocity normal to the coast. It is shown that the balance equations also support coastal Kelvin waves, but these waves differ depending upon the boundary conditions imposed. Three different boundary conditions and...
The effects of alongshore variations in bottom topography and coastline on the wind-stress-forced barotropic motion over a continental shelf and slope are studied. Perturbation methods are used to obtain solutions for forced and free continental shelf waves on an idealized continental shelf and slope with small-amplitude alongshore variations in topography....
Intermediate models contain physics between that in the primitive equations and that in the quasigeostrophic equations. The specific objective here is to investigate the absolute and relative accuracy of several intermediate models for stratified flow by a comparison of numerical finite-difference solutions with those of the primitive equations (PE) and...
Time-dependent downwelling on the Oregon continental shelf is studied with a two-dimensional approximation, that is, spatial variations across shelf and with depth, using the Blumberg-Mellor, finite-difference, stratified, hydrostatic, primitive equation model. The time-dependent response of a coastal ocean at rest to constant, downwelling-favorable wind stress is examined. Topography and stratification...
The study of intermediate models for barotropic continental shelf and slope flow fields initiated in Parts I and II is continued. The objective is to investigate the possible use of intermediate models for process and data assimilation studies of nonlinear mesoscale eddy and jet current fields over the continental shelf...
An analysis is presented of low-frequency (<0.4 cpd) fluctuations in currents, temperature and tide gage data collected during the March-September 1976 segment of the CUEA JOINT-II experiment off the coast of Peru. The observations were made near 15°S, a region of particularly strong and persistent coastal upwelling. Conclusions about the...
A two-layer model with an idealized continental shelf and slope bottom topography is utilized to study some properties of the response of stratified coastal regions to meteorological forcing with variations in the alongshore direction. The model is such that the coastline is straight, there are no alongshore variations in the...
A two-dimensional, frictionless, nonlinear model of coastal upwelling is reexamined. The model has been solved previously at steady state and as an initial-value problem. The previous solution to the initial-value problem is inconsistent with the steady-state solution. A new solution to the spinup problem is presented that approaches the existing...
As part of a study of the large-scale response of coastal sea level to atmospheric forcing along the west coast of North America during June–September 1973, Halliwell and Allen calculate space- and time-lagged cross-correlation coefficients Rτζ between adjusted sea level ζ at fixed alongshore locations ζ(y0) and the alongshore component...
Model studies of two-dimensional, time-dependent, wind-forced, stratified downwelling circulation on the continental shelf have shown that the near-bottom offshore flow can develop time- and space-dependent fluctuations involving spatially periodic separation and reattachment of the bottom boundary layer and accompanying recirculation cells. Based primarily on the observation that the potential vorticity...
Satellite along-track sea surface height (SSH) and multisatellite sea surface temperature (SST) maps are assimilated in a coastal ocean circulation model off Oregon. The study period is June–October 2005, featuring intensive separation of the coastal upwelling jets in the eddy-dominated coastal transition zone (CTZ). The data assimilation (DA) system combines...
Velocity measurements from the continental shelf off Oregon taken during the Coastal Upwelling Experiment CUE-2 in the summer of 1973 are utilized to investigate momentum, vorticity and mass balance relationships for subinertial frequency (ω < 0.6 cpd) current fluctuations. Measurements from stations in water of depths of 54, 100 and...
Intermediate models contain physics between that in the primitive equations and that in the quasigeostrophic equations and are capable of representing subinertial frequency motion over O(1) topographic variations typical of the continental slope while filtering out high-frequency gravity-inertial waves. We present here a formulation for stratified flow of a set...
The behavior of low-frequency baroclinic Rossby wave motion in the vicinity of coastal boundaries is investigated using linearized modulated wave theory in a stratified, constant-depth, equatorial β-plane ocean. A primary objective is to obtain an equation that describes large-scale, low-frequency pressure fluctuations along variable geometry ocean boundaries at all latitudes...
An approximate model for small Rossby number ϵ that is close to the balance equations (BE) but that is based on approximate momentum equations is formulated for a rotating, continuously stratified fluid governed by the hydrostatic, Boussinesq, inviscid, adiabatic primitive equations with spatially variable Coriolis parameter. This model, referred to...
The effect of bottom friction on the subinertial frequency motion of stratified shelf flow fields is studied in a two-layer ƒ-plane model with idealized shelf and slope bottom topography. Coastal-trapped fire waves and motion forced by the alongshore component of the wind stress at the coast are considered. Vertical turbulent-diffusion...
Nonlinear model simulations of a coastal upwelling system show frontal instabilities that initiate at short alongshore scales but rapidly evolve to longer wavelengths. Several factors associated with the nonstationarity of this basic state contribute to the progression in scale. A portion of the system evolution is associated with the external...
A primitive equation model is used to study the finite-amplitude evolution of instabilities associated with the coastal upwelling front. Simulations of increasing complexity are examined that represent idealizations of summer conditions off the Oregon coast, including cases with steady and with time-variable wind in a domain with alongshore-uniform bathymetry and...
Previous studies of forced, long continental shelf waves on an ƒ-plane have considered motion on the shelf and slope which is driven by an alongshore component of the wind stress, essentially through the suction of fluid into the surface layer at the coast. These studies have utilized a boundary condition,...
Empirical orthogonal function (EOF) analysis in the frequency domain is extended to complex time series. EOFs are calculated from the eigenvectors of the band-averaged rotary cross-spectral matrix. This gives EOF amplitude and phase for negative and positive frequencies, corresponding to clockwise and anticlockwise rotation for the hodograph model. Rotary EOF...
The generation of an alongshore mean flow by the nonlinear interaction of forced barotropic shelf waves over a continental margin is studied using a wind-forced, ƒ-plane model with bottom friction in an attempt to develop a model for poleward eastern boundary undercurrents. It is assumed that the Rossby number is...
Three‐dimensional circulation in the coastal transition zone (CTZ) off Oregon is
studied using a 3 km resolution model based on the Regional Ocean Modeling System.
The study period is spring and summer 2002, when extensive observations were available
from the northeastern Pacific component of the Global Ocean Ecosystems Dynamics
project....
The dynamics of the coastal transition zone off Northern California during late May and early June 1987 art
examined through assimilation modeling studies. A regional baroclinic quasi-geostrophic model is driven by the
data through initial and boundary conditions. These initial and boundary conditions are specified by objective
analysis of hydrographic...
A study of swash zone sediment transport was conducted at Gleneden
Beach, Oregon during February 25-28, 1994. The data collected included suspended
sediment concentration (SSC), sea surface elevation, and velocity (initially 4 and 8
cm above the bed) at three cross-shore locations within the swash zone spanning high
tides. Ensemble...
The nonlinear dynamics of finite amplitude shear instabilities of
alongshore currents in the nearshore surf zone over barred beach topography are
studied using numerical experiments. These experiments extend the recent study
of Allen et al. [1996], which utilized plane beach (constant slope) topography by
including shore-parallel sandbars. The model involves...
The nonlinear dynamics of unstable alongshore currents in the nearshore
surf zone over variable barred beach topography are studied using numerical
experiments. These experiments extend the recent studies of Allen et al. [1996]
and Slnn et al. [1998], which utilized alongshore uniform beach topographies by
including sinusoidal alongshore variation to...