A model of a Mediterranean salt lens in external shear
Citable URI
https://hdl.handle.net/1912/5488Location
Eastern North AtlanticDOI
10.1575/1912/5488Keyword
Water masses; Fluid dynamics; EddiesAbstract
A pair of simple models representing the interaction of a continuously stratified f-plane quasigeostrophic
lens with a uniform external shear flow is examined. The study is motivated by the
desire to understand the processes that affect Mediterranean Salt Lenses and other mesoscale lenses
in the ocean. The first model represents the eddy as a pair of quasigeostrophic 'point potential
vortices' in uniform external shear, where the two point vortices are imagined to represent the
top and bottom of a baroclinic eddy. While highly idealized, the model succeeds in qualitatively
reproducing many aspects of the behavior of more complex models. In the second model the eddy
is represented by an isolated three dimensional patch characterized by quasigeostrophic potential
vorticity linear in z, in a background flow with constant potential vorticity. The boundary of the
lens may be deformed by interactions with a uniform background shear. A family of linearized
analytical solutions representing such a vortex is discussed in Chapter 3. These solutions represent
lens-like eddies with trapped fluid cores, which may propagate through the surrounding water when
there is external vertical shear. The analysis predicts the possible forms of the boundary deformation
in a specified external flow, and the precession rate of normal mode boundary perturbations
in the absence of external flow. The translation speed of the lens with respect to the surrounding
fluid is found to be a simple function of the external vertical shear and the core baroclinicity.
A numerical algorithm which is a generalization of the contour dynamics technique to stratified
quasigeostrophic flow is used to extend the linear results into the nonlinear regime. This
numerical analysis allows a determination of the range of environmental conditions (e.g., the maximum
shear and/ or core baroclinicity) in which coherent vortex solutions can be found, and allows
the stability of the steadily translating solutions to be examined directly. It is found that the
solutions are stable if neither the external shear nor the core baroclinicity is too large, and that the
breakdown of the unstable solutions is characterized by the loss of an extrusion of core fluid to the
surrounding waters. The translation speeds of the large amplitude numerical solutions are found
to have the same functional dependence on the external vertical shear and the core baroclinicity
that was found in the linear analysis, and it is demonstrated that the solutions translate at a rate
which is equal to the background flow speed at the center of potential vorticity of the lens. As a test of the model results, new data from a recent SOFAR float experiment are presented
and compared with the model predictions. The data show that the cores of two different
Mediterranean Salt Lenses are tilted, presumably as a result of interactions with external flows.
Both the sense of the tilt and its relation to the translation of the lens are in qualitative agreement
with the model solutions.
Description
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution April 1992
Collections
Suggested Citation
Thesis: Walsh, David, "A model of a Mediterranean salt lens in external shear", 1992-04, DOI:10.1575/1912/5488, https://hdl.handle.net/1912/5488Related items
Showing items related by title, author, creator and subject.
-
Biotic and abiotic interactions of deep-sea hydrothermal vent-endemic fish on the East Pacific Rise
Buckman, Kate Lynn (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2009-09)A study of the ecology of fish endemic to hydrothermal vents on the East Pacific Rise was undertaken utilizing a variety of techniques, focusing on the bythitid Thermichthys hollisi. Stable isotope and gut content analyses ... -
Forward sound propagation around seamounts : application of acoustic models to the Kermit-Roosevelt and Elvis seamounts
Kim, Hyun Joe (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2009-06)The Basin Acoustic Seamount Scattering Experiment (BASSEX) of 2004 was conducted to measure forward-scattering around the Kermit-Roosevelt Seamount Complex in the Northeast Pacific. The BASSEX experiment was focused on ... -
Vertical distributions of temperature and humidity over the ocean between Nantucket and New Jersey
Emmons, Gardner (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1947-12)This paper is concerned with the results of a series of airplane psychrometer soundings that were made over the ocean up to a height of 1500 ft during June, 1945. These soundings and previous soundings already described ...