Brink Kenneth H.

Last Name

Brink

First Name

Kenneth H.

Full item page

Search Results

Now showing 1 - 20 of 22

Topographic rectification in a stratified ocean

(Sears Foundation for Marine Research, 2011-07-01) Brink, Kenneth H.

Mean flow generation by oscillating currents is considered in an idealized stratified ocean with a corrugated shelf-slope topography. Numerical model results for near-bottom mean along-isobath flow show a general parameter dependence similar to that found with no stratification (Brink, 2010). Stratification, however, makes the interior rectified flow depth-dependent, and usually bottom-intensified. Scalings for both the mean flow and its vertical dependence are developed and evaluated. Two crude comparisons against observed mean oceanic flows suggest that the present results may parameterize the mean flow magnitude correctly.
Some considerations about coastal ocean observing systems

(Sears Foundation for Marine Research, 2017-05-01) Brink, Kenneth H. ; Kirincich, Anthony R.

Coastal ocean observing capabilities are evolving rapidly, both in terms of sensors and in terms of the volume of information available. We discuss the aspects of the coastal ocean that make it a unique environment, both in terms of physical processes and measurement techniques. Although many global-level systems are relevant to the coastal ocean, we concentrate on treating systems that are unique to the continental shelf environment. Further, we briefly discuss examples of measurement systems that would be useful for developing and driving ocean prediction systems.
Topographic rectification in a forced, dissipative, barotropic ocean

(Sears Foundation for Marine Research, 2010-05-01) Brink, Kenneth H.

Barotropic current rectification by topographic irregularities is treated for a case with bottom friction and fluctuating forcing. Geometries both with underlying shelf-slope topography and with no mean topographic slope are considered. In common with many previous studies of this sort, the resulting time-mean flow roughly follows isobaths in the direction that long topographic Rossby waves travel, but the mean flow often deviates locally from this rule. Further, as might be expected, there is an area-averaged correlation of pressure and bottom slope in the sense that would propel the mean flow. If the topographic irregularities have a length scale shorter than roughly a particle fluctuation excursion, then the typical along-isobath mean flow is proportional to the bottom slope, the irregularity length scale, the amplitude of the cross-isobath velocity fluctuations, and the inverse of the water depth. If the spatial scale of the irregularities is greater than roughly a particle excursion, then the resulting mean flow does not depend on irregularity length scale, but does depend on the Coriolis parameter, the bottom slope, cross-isobath velocity squared, the inverse depth and the inverse frequency squared. For large amplitude fluctuations, eddy momentum transport leads to a further inverse proportionality of mean flow to the strength of bottom friction. The overall mean flow parameterization holds only in a statistical sense (as opposed to point-by-point) because of the spatial complexity of typical flows. In a forced, dissipative system, the mean flow generation is often just tidal rectification (e.g., Loder, 1980) if the particle excursion is short relative to topographic scales. However, as the irregularity scale decreases, mean flow becomes weaker.
What determines the spatial pattern in summer upwelling trends on the U.S. West Coast?

(American Geophysical Union, 2012-08-09) Seo, Hyodae ; Brink, Kenneth H. ; Dorman, Clive E. ; Koracin, Darko ; Edwards, Christopher A.

Analysis of sea surface temperature (SST) from coastal buoys suggests that the summertime over-shelf water temperature off the U.S. West Coast has been declining during the past 30 years at an average rate of −0.19°C decade−1. This cooling trend manifests itself more strongly off south-central California than off Oregon and northern California. The variability and trend in the upwelling north of off San Francisco are positively correlated with those of the equatorward wind, indicating a role of offshore Ekman transport in the north. In contrast, Ekman pumping associated with wind stress curls better explains the stronger and statistically more significant cooling trend in the south. While the coast-wide variability and trend in SST are strongly correlated with those of large-scale modes of climate variability, they in general fail to explain the southward intensification of the trend in SST and wind stress curl. This result suggests that the local wind stress curl, often topographically forced, may have played a role in the upwelling trend pattern.
Rossby waves with continuous stratification and bottom friction

(American Meteorological Society, 2018-09-17) Brink, Kenneth H. ; Pedlosky, Joseph

Published observations of subinertial ocean current variability show that the vertical structure is often well described by a vertical mode that has a node of horizontal velocity at the bottom rather than the traditional node of vertical velocity. The theory of forced and free linear Rossby waves in a continuously stratified ocean with a sloping bottom and bottom friction is treated here to see if frictional effects can plausibly contribute to this phenomenon. For parameter values representative of the mesoscale, bottom dissipation by itself appears to be too weak to be an explanation, although caution is required because the present approach uses a linear model to address a nonlinear phenomenon. One novel outcome is the emergence of a short-wave, bottom-trapped, strongly damped mode that is present even with a flat bottom.
Buoyancy arrest and shelf–ocean exchange

(American Meteorological Society, 2012-04) Brink, Kenneth H.

When steady flow in a stratified ocean passes between the continental slope and open ocean, its ability to cross isobaths is potentially limited by buoyancy arrest. If the bottom Ekman transport vanishes and there are no interior stresses, then steady linear flow on an f plane must be geostrophic and follow isobaths exactly. The influence of arrest on cross-shelf transport is investigated here to establish 1) whether there are substantial penetration asymmetries between cases with upwelling and downwelling in the bottom boundary layer; 2) over what spatial scales, hence in what parameter regime, buoyancy arrest is important; and 3) the effects of depth-dependent interior flow. The problem is approached using scalings and idealized numerical models. The results show that there is little or no asymmetry introduced by bottom boundary layer behavior. Further, if the stratification is weak or moderate, as measured by a slope Burger number s = αN/f (where α is the bottom slope, N is buoyancy frequency, and f is the Coriolis parameter), buoyancy arrest does not exert a strong constraint on cross-isobath exchange.
A new era for The Sea

(Sears Foundation for Marine Research, 2017-05-01) Brink, Kenneth H. ; McCarthy, James J.
Near-resonances of superinertial and tidal fluctuations at islands

(American Meteorological Society, 2021-08-12) Brink, Kenneth H.

A linear numerical model of an island or a tall seamount is used to explore superinertial leaky resonances forced by ambient vertically and horizontally uniform current fluctuations. The model assumes a circularly symmetric topography (including a shallow reef) and allows realistic stratification and bottom friction. As long as there is substantial stratification, a number of leaky resonances are found, and when the island’s flanks are narrow relative to the internal Rossby radius, some of the near-resonant modes resemble leaky internal Kelvin waves. Other “resonances” resemble higher radial mode long gravity waves as explored by Chambers. The near-resonances amplify the cross-reef velocities that help fuel biological activity. Results for cases with the central island replaced by a lagoon do not differ greatly from the island case which has land at the center. As an aside, insight is provided on the question of offshore boundary conditions for superinertial nearly trapped waves along a straight coast.
Rectified flow in a stratified coastal ocean

(Sears Foundation for Marine Research, 2018-01) Brink, Kenneth H.

An idealized numerical model is used to explore the generation of mean flows by oscillating wind forcing in a stratified coastal ocean with no alongshore variability, i.e., where neither barotropic nor baroclinic instability is a factor. On the inner shelf, where surface-to-bottom mixing occurs, a mean cross-shelf flow develops, as examined by Castelao et al. (2010), and the present results suggest that this flow can remain two-dimensional if there is a nonzero cross-shelf density gradient. Offshore of the inner shelf, where the water column is stratified, a mean alongshore flow develops in the direction opposite to coastal-trapped wave propagation. This flow is associated with cross-shelf density gradients that are set up by the asymmetry between onshore and offshore flow in the bottom boundary layer. Both forms of rectified flow (cross-shelf and alongshore) are sensitive to the presence of surface heating, and the rectifications can be readily masked by the effect of a steady alongshore wind stress.
Offshore transport of shelf water by deep-ocean eddies

(American Meteorological Society, 2016-12-08) Cherian, Deepak A. ; Brink, Kenneth H.

At continental margins, energetic deep-ocean eddies can transport shelf water offshore in filaments that wrap around the eddy. One example is that of Gulf Stream warm-core rings interacting with the Mid-Atlantic Bight shelf. The rate at which shelf water is exported in these filaments is a major unknown in regional budgets of volume, heat, and salt. This unknown transport is constrained using a series of idealized primitive equation numerical experiments wherein a surface-intensified anticyclonic eddy interacts with idealized shelf–slope topography. There is no shelfbreak front in these experiments, and shelf water is tracked using a passive tracer. When anticyclones interact with shelf–slope topography, they suffer apparent intrusions of shelf–slope water, resulting in a subsurface maximum in offshore transport. The simulations help construct an approximate model for the filament of exported water that originates inshore of any given isobath. This model is then used to derive an expression for the total volume of shelf–slope water transported by the eddy across that isobath. The transport scales with water depth, radius, and azimuthal velocity scale of the eddy. The resulting expression can be used with satellite-derived eddy properties to estimate approximate real-world transports ignoring the presence of a shelfbreak front. The expression assumes that the eddy’s edge is at the shelf break, a condition not always satisfied by real eddies.
Evaporative dense water formation and cross-shelf exchange over the northwest Australian inner shelf

(American Geophysical Union, 2010-06-29) Shearman, R. Kipp ; Brink, Kenneth H.

High-resolution surveys of oceanographic and atmospheric conditions made during the winter over the inner shelf off northwest Australia are used to examine the coastal ocean response to large outgoing heat and freshwater fluxes. Relatively cool, low-humidity air blows off the Australian continent out over the tropical continental shelf, resulting in a large mean latent heat flux (−177 W m−2) that overwhelms insolation and, along with the outgoing long-wave radiation, results in substantial net cooling (−105 W m−2) and evaporative freshwater flux (0.6 cm d−1). The inner shelf is characterized by increasingly cool, salty, and dense waters onshore, with a strong front near the 25 m isobath. The front is evident in satellite sea surface temperature (SST) imagery along the majority of the northwest Australian shelf, exhibiting a complex filamentary and eddy structure. Cross-shelf buoyancy fluxes estimated from the mean, two-dimensional heat and salt budgets are comparable to parameterizations of cross-shelf eddy driven fluxes; however, the same fluxes can be achieved by cross-shelf transports in the bottom boundary layer of about 0.5 m2 s−1 (and an overlying return flow).
Buoyancy arrest and bottom Ekman transport. Part II : oscillating flow

(American Meteorological Society, 2010-04) Brink, Kenneth H. ; Lentz, Steven J.

The effects of a sloping bottom and stratification on a turbulent bottom boundary layer are investigated for cases where the interior flow oscillates monochromatically with frequency ω. At higher frequencies, or small slope Burger numbers s = αN/f (where α is the bottom slope, N is the interior buoyancy frequency, and f is the Coriolis parameter), the bottom boundary layer is well mixed and the bottom stress is nearly what it would be over a flat bottom. For lower frequencies, or larger slope Burger number, the bottom boundary layer consists of a thick, weakly stratified outer layer and a thinner, more strongly stratified inner layer. Approximate expressions are derived for the different boundary layer thicknesses as functions of s and σ = ω/f. Further, buoyancy arrest causes the amplitude of the fluctuating bottom stress to decrease with decreasing σ (the s dependence, although important, is more complicated). For typical oceanic parameters, arrest is unimportant for fluctuation periods shorter than a few days. Substantial positive (toward the right when looking toward deeper water in the Northern Hemisphere) time-mean flows develop within the well-mixed boundary layer, and negative mean flows exist in the weakly stratified outer boundary layer for lower frequencies and larger s. If the interior flow is realistically broad band in frequency, the numerical model predicts stress reduction over all frequencies because of the nonlinearity associated with a quadratic bottom stress. It appears that the present one-dimensional model is reliable only for time scales less than the advective time scale that governs interior stratification.
Bottom boundary layer flow and salt injection from the continental shelf to slope

(American Geophysical Union, 2006-07-14) Brink, Kenneth H. ; Shearman, R. Kipp

Austral winter oceanographic measurements from the northwest Australian continental shelf reveal salty water forming evaporatively inshore, moving across the wide shelf near the bottom and into the adjacent open ocean when the shelf edge alongshore flow is equatorward. The salt tongue is absent during more normal conditions, when the poleward Leeuwin Current is present. We hypothesize that the flow reversal enables shelf-wide bottom boundary layer (Ekman) transport and thus creates the shelf-edge convergence that accounts for the observed salt tongue. This flow is absent under sustained normal conditions because of buoyancy arrest in the bottom boundary layer.
Pathways and mechanisms of offshore water intrusions on the Espírito Santo Basin shelf (18°S–22°S, Brazil)

(John Wiley & Sons, 2016-07-30) Palóczy, Andre ; Brink, Kenneth H. ; da Silveira, Ilson C. A. ; Arruda, Wilton Z. ; Martins, Renato P.

The pathways and physical mechanisms associated with intrusions of cold, nutrient-rich South Atlantic Central Water (SACW) on the continental shelf of the Espírito Santo Basin (ESB), off southeast Brazil (18°S–22°S), are investigated. To this end, a set of process-oriented, Primitive-Equation (PE) numerical models are used, together with an independent and more complete PE model, available observations and simple theoretical ideas. SACW enters the model ESB shelf mostly through two preferential pathways along the Tubarão Bight (TB, 19.5°S–22°S). These pathways are found to be locations where an equatorward along-isobath pressure gradient force (PGFy*) of inline image m s−2) develops in response to steady wind forcing. This equatorward PGFy* is essentially in geostrophic balance, inducing onshore flow across the shelf edge, and most of the shelf proper. The Brazil Current (BC) imparts an additional periodic (in the along-shelf direction) PGFy* on the shelf. The intrinsic pycnocline uplifting effect of the BC in making colder water available at the shelf edge is quantified. The BC also induces local intrusions by inertially overshooting the shelf edge, consistent with estimated Rossby numbers of inline image0.3–0.5. In addition, the planetary β-effect is related to a background equatorward PGFy*. A modified Arrested Topographic Wave model is shown to be a plausible rationalization for the shelf-wide spreading of the pressure field imparted by the BC at the shelf edge. The deep-ocean processes examined here are found to enhance the onshore transport of SACW, while wind forcing is found to dominate it at leading order.
Buoyancy arrest and bottom Ekman transport. Part I : steady flow

(American Meteorological Society, 2010-04) Brink, Kenneth H. ; Lentz, Steven J.

It is well known that along-isobath flow above a sloping bottom gives rise to cross-isobath Ekman transport and therefore sets up horizontal density gradients if the ocean is stratified. These transports in turn eventually bring the along-isobath bottom velocity, hence bottom stress, to rest (“buoyancy arrest”) simply by means of the thermal wind shear. This problem is revisited here. A modified expression for Ekman transport is rationalized, and general expressions for buoyancy arrest time scales are presented. Theory and numerical calculations are used to define a new formula for boundary layer thickness for the case of downslope Ekman transport, where a thick, weakly stratified arrested boundary layer results. For upslope Ekman transport, where advection leads to enhanced stability, expressions are derived for both the weakly sloping (in the sense of slope Burger number s = αN/f, where α is the bottom slope, N is the interior buoyancy frequency, and f is the Coriolis parameter) case where a capped boundary layer evolves and the larger s case where a nearly linearly stratified boundary layer joins smoothly to the interior density profile. Consistent estimates for the buoyancy arrest time scale are found for each case.
Observations of storm-induced mixing and Gulf Stream Ring incursion over the southern flank of Georges Bank : winter and summer 1997

(American Geophysical Union, 2010-08-07) Lee, Craig M. ; Brink, Kenneth H.

High-resolution hydrographic measurements collected along the southern edge of Georges Bank during March and June–July 1997 focused on characterizing processes that drive fluxes of material between the slope and bank. Wintertime sampling characterized changes driven by a strong storm. A Scotian Shelf crossover event produced a ribbon of anomalously fresh water along the bank's southern flank that was diluted during the storm. Comparison of prestorm and poststorm sections shows that over the bank changes in heat and salt inventories are consistent with those expected solely from local surface fluxes. In deeper waters, advective effects, likely associated with frontal motion and eddies, are clearly important. Summertime surveys resolve the development of a massive intrusion of Gulf Stream-like waters onto the bank. East of the intrusion, a thin extrusion of bank water is drawn outward by the developing ring, exporting fresher water at a rate of about 7 × 104 m3/s. A large-amplitude Gulf Stream meander appears to initiate the extrusion, but it quickly evolves, near the bank edge, into a warm core ring. Ring water intrudes to approximately the 80 m isobath, 40 km inshore from the bank edge. The intrusion process seems analogous to the development of Gulf Stream shingles (a hydrodynamic instability) in the South Atlantic Bight. It appears that, once the intruded water is established on the bank, it remains there and dissipates in place. Although the intrusion is an extremely dramatic event, it is probably not actually a major contributor to shelf edge exchanges over a seasonal time scale.
Surface cooling, winds, and eddies over the continental shelf

(American Meteorological Society, 2017-04-17) Brink, Kenneth H.

Models show that surface cooling over a sloping continental shelf should give rise to baroclinic instability and thus tend toward gravitationally stable density stratification. Less is known about how alongshore winds affect this process, so the role of surface momentum input is treated here by means of a sequence of idealized, primitive equation numerical model calculations. The effects of cooling rate, wind amplitude and direction, bottom slope, bottom friction, and rotation rate are all considered. All model runs lead to instability and an eddy field. While instability is not strongly affected by upwelling-favorable alongshore winds, wind-driven downwelling substantially reduces eddy kinetic energy, largely because the downwelling circulation plays a similar role to baroclinic instability by flattening isotherms and so reducing available potential energy. Not surprisingly, cross-shelf winds appear to have little effect. Analysis of the model runs leads to quantitative relations for the wind effect on eddy kinetic energy for the equilibrium density stratification (which increases as the cooling rate increases) and for eddy length scale.
Instability of an idealized tidal mixing front : symmetric instabilities and frictional effects

(Sears Foundation for Marine Research, 2013-11-01) Brink, Kenneth H. ; Cherian, Deepak A.

Finite amplitude instability of an idealized tidal mixing front is considered for cases where there is an active symmetric instability during the early stages of evolution. This can happen either when the initial front is sharp, or when a bottom stress leads to a well-mixed bottom boundary layer under the front. In either case, there is an initial phase, several days long, of slantwise convection, after which a much more energetic and spatially distributed baroclinic or barotropic instability dominates. The presence of an initial symmetrically unstable phase has no obvious effect on the subsequent eddy evolution. Bottom friction does lead to a slower growth rate for baroclinic instabilities, a lower eddy kinetic energy level, and (through stratified spindown) a tendency for flows to be more nearly surface intensified. The surface intensification means that the evolving eddy field cannot proceed toward a barotropic state, and so the horizontal eddy scale is also constrained. Thus, the finite-amplitude inverse cascade is strongly affected by the presence of a bottom stress. Scalings are derived for the frictionally corrected eddy kinetic energy and lateral mixing coefficient. The results, in terms of frictional effects on eddy structure and energy, appear to be valid beyond just the tidal mixing frontal problem.
A large-amplitude meander of the shelfbreak front during summer south of New England : observations from the Shelfbreak PRIMER experiment

(American Geophysical Union, 2004-03-04) Gawarkiewicz, Glen G. ; Brink, Kenneth H. ; Bahr, Frank B. ; Beardsley, Robert C. ; Caruso, Michael J. ; Lynch, James F. ; Chiu, Ching-Sang

In order to examine spatial and temporal variability of the shelfbreak front during peak stratification, repeated surveys using a towed undulating vehicle (SeaSoar) are used to describe the evolution of shelfbreak frontal structure during 26 July to 1 August 1996 south of New England. Spatial correlation (e-folding) scales for the upper 60 m of the water column were generally between 8 and 15 km for temperature, salinity, and velocity. Temporal correlation scales were about 1 day. The frontal variability was dominated by the passage of a westward propagating meander that had a wavelength of 40 km, a propagation speed of 0.11 m s−1, and an amplitude of 15 km (30 km from crest to trough). Along-front geostrophic velocities (referenced to a shipboard acoustic Doppler current profilers) were as large as 0.45 m s−1, although subject to significant along-front variations. The relative vorticity within the jet was large, with a maximum 0.6 of the local value of the Coriolis parameter. Seaward of the front, a small detached eddy consisting of shelf water was present with a diameter of approximately 15 km. Ageostrophic contributions to the velocity field are estimated to be as large as 0.3 m s−1 in regions of sharp curvature within the meander. These observations strongly suggest that during at least some time periods, shelfbreak exchange is nonlinear (large Rossby number) and dominated by features on a horizontal scale of order 10 km.
Continental shelf baroclinic instability. Part I : relaxation from upwelling or downwelling

(American Meteorological Society, 2015-12-09) Brink, Kenneth H.

There exists a good deal of indirect evidence, from several locations around the world, that there is a substantial eddy field over continental shelves. These eddies appear to have typical swirl velocities of a few centimeters per second and have horizontal scales of perhaps 5–10 km. These eddies are weak compared to typical, wind-driven, alongshore flows but often seem to dominate middepth cross-shelf flows. The idea that motivates the present contribution is that the alongshore wind stress ultimately energizes these eddies by means of baroclinic instabilities, even in cases where obvious intense fronts do not exist. The proposed sequence is that alongshore winds over a stratified ocean cause upwelling or downwelling, and the resulting horizontal density gradients are strong enough to fuel baroclinic instabilities of the requisite energy levels. This idea is explored here by means of a sequence of idealized primitive equation numerical model studies, each driven by a modest, nearly steady, alongshore wind stress applied for about 5–10 days. Different runs vary wind forcing, stratification, bottom slope, bottom friction, and Coriolis parameter. All runs, both upwelling and downwelling, are found to be baroclinically unstable and to have scales compatible with the underlying hypothesis. The model results, combined with physically based scalings, show that eddy kinetic energy generally increases with bottom slope, stratification, wind impulse (time integral of the wind stress), and inverse Coriolis parameter. The dominant length scale of the eddies is found to increase with increasing eddy kinetic energy and to decrease with Coriolis parameter.

Brink Kenneth H.

Last Name

First Name

ORCID

Filters

Author

Subject

Date

Type

Has files

Settings

Sort By

Results per page

Search Results