131 research outputs found

    Island-trapped waves with stratification, topography, mean flow and bottom friction in Matlab

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    This set of Matlab mfiles (all having names that begin with “bigi”) can be used to calculate island-trapped wave modal structures and dispersion curves under very general circumstances for a circular island. A complex frequency is allowed, so that instability and damping can be accounted for directly. Modal structures and energy diagnostics are provided. For most applications, the code is only useful for subinertial wave frequencies (i.e., the real part of wave frequency is smaller than the Coriolis parameter). For interpreting the model results, see Brink (1999), which deals with the case with no mean flow or finite bottom friction. The present code was developed independently of the Fortran code used in that publication

    Continental shelf baroclinic instability. Part I : relaxation from upwelling or downwelling

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    Author Posting. © American Meteorological Society, 2015. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 46 (2016): 551-568, doi:10.1175/JPO-D-15-0047.1.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.This work was supported by the Woods Hole Oceanographic Institution and by the National Science Foundation, Physical Oceanography section through Grant OCE-1433953.2016-06-0

    Cross-shelf exchange

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    Author Posting. © The Author(s), 2015. This is the author's version of the work. It is posted here by permission of Annual Reviews for personal use, not for redistribution. The definitive version was published in Annual Review of Marine Science 8 (2016): 59-78, doi:10.1146/annurev-marine-010814-015717.Cross-shelf exchange dominates the pathways and rates by which nutrients, biota and materials on the continental shelf are delivered and removed. These transports are limited by Earth’s rotation, which inhibits flow from crossing isobaths. Thus, cross-shelf transports are generally weak compared to alongshore flows, and this leads to interesting observational issues. Cross-shelf flows are enabled by turbulent mixing processes, by nonlinear processes (such as momentum advection), and by time-dependence. Thus, there is a wide range of possible effects that can allow these critical transports, and different natural settings are often governed by differing mixes of processes. Examples of representative transport mechanisms are discussed, and possible observational and theoretical paths to future progress are explored.Support from the National Science Foundation Physical Oceanography program, through grant OCE-1433953, and the Biological Oceanography program through grant OCE-125866

    Rectified flow in a stratified coastal ocean

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    Author Posting. © The Author, 2018. This article is posted here by permission of [publisher] for personal use, not for redistribution. The definitive version was published in Journal of Marine Research 76 (2018): 1-22, doi:10.1357/002224018824082016.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.This research was partially supported by the National Science Foundation Physical Oceanography Program through grant OCE-1433953

    Surface cooling, winds, and eddies over the continental shelf

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    Author Posting. © American Meteorological Society, 2017. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 47 (2017): 879-894, doi:10.1175/JPO-D-16-0196.1.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.This research was supported by the National Science Foundation Physical Oceanography Program through Grant OCE-1433953

    Barotropic coastal trapped wave modes with complex frequency: edge, shelf and Kelvin waves

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    This set of Matlab mfiles (all with names beginning with “bwavesc”) can be used to calculate barotropic coastal wave properties in the absence of density stratification. The wave frequency is complex so that unstable or strongly damped modes can be treated. You are allowed to have a mean alongshore flow, if desired, and you can apply the rigid lid approximation. The model can be run in the non-rotating limit if desired. Once a wave’s frequency is found, the modal structure is displayed. The code can use an exact open boundary condition or a closed condition at either side of the domain

    Editor\u27s Commentary: Effect of Coriolis force on edge waves (I) Investigation of the normal modes

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    In the oceanographic literature, there are not too many publications so clearly ahead of their time as is this one. Reid starts out by asking about the effect of Earth’s rotation on edge waves. Edge waves are essentially long gravity waves found over the continental shelf and up onto the beach. They are topographically constrained to propagate strictly alongshore, but in either direction. By the mid-1950s, interest in this was growing as people realized that edge waves are more than a mathematical curiosity. Rotation was expected to be important for long, low frequency (periods of tens of minutes, out to hours) waves, so the contribution was timely..

    Editor\u27s Commentary: Steady flow in a frictionless homogenous ocean

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    Before the publication of this article, Stommel (1948) and Munk (1950) published their linear, frictional models of steady wind-driven ocean gyres. The innovative advance they introduced was that their models included western boundary currents (e.g., the Gulf Stream)for the first time. These were really exciting advances. Yet, these models had some dreamlike qualities (to paraphrase Stommel) in that the flow patterns were very smooth, that the intense current always hugged the western boundary, and that the eastward interior flow is broadly distributed across latitudes..

    Editor\u27s Commentary: On the process of upwelling

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    Although Harald Sverdrup is now probably best known for his work on basin-scale ocean circulation, his interests were remarkably diverse, and included continental shelf processes. As a coastal oceanographer, I can’t resist highlighting this contribution to the coastal upwelling literature. A relatively simple data set is exploited here, consisting of cross-shelf sections taken near Point Conception, California..

    Editorial

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    With the completion of Volume 67 of the Journal of Marine Research, George Veronis is stepping down after having served as editor for 37 years. In the Journal’s 73-year history, there have been only three editors, and George has served the longest. During George’s tenure, the Journal has prospered and it has strengthened its position as one of the best oceanographic scholarly Journals. The entire oceanographic community should be grateful for George’s commitment to excellence, hard work and commitment. His accomplishments with the Journal are most impressive
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