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dc.contributor.authorAlverson, Keith D.  Concept link
dc.coverage.spatialMaud Rise
dc.coverage.spatialWeddell Sea
dc.date.accessioned2012-12-13T19:34:17Z
dc.date.available2012-12-13T19:34:17Z
dc.date.issued1995-09
dc.identifier.urihttps://hdl.handle.net/1912/5618
dc.descriptionSubmitted 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 September 1995en_US
dc.description.abstractEvidence of enhanced oceanic convection over Maud Rise in the Weddell Sea indicates that bottom topography may play a role in selecting the location and scale of deep convecting oceanic chimneys below large scale atmospheric negative buoyancy forcing. Topographic preconditioning of open ocean deep convection is studied using an idealized, three-dimensional, primitive-equation model. A barotropic mean flow impinges on an isolated Gaussian-shaped seamount in a stratified domain with uniform negative surface buoyancy forcing. A region of topographically trapped flow forms over the topography. When this "Taylor cap" is tall enough to interact with the surface mixed-layer, the local isolation from mean horizontal advection forms a conduit into the deep water. The convective penetration depth within this local region is significantly enhanced relative to ambient levels away from the seamount and to similar runs performed without bottom topography. The parameter dependencies for these preconditioning processes are investigated. With uniform background stratification, the doming of isopycnals does not play a major role in the preconditioning process. However, when a surface intensified stratification is included, domed isopycnals associated with the Taylor cap circulation can also play a preconditioning role. In this case, the pycnocline is first ventilated over the seamount, leading to rapid convective deepening into the weakly stratified deep water. An analytical formula for one-dimensional, non-penetrative convection into an exponential stratification profile is derived and compares well with results from the numerical model. Previous modeling studies have often parameterized the mehanism by which the horizontal scale of oceanographic chimneys is set through the use of disk-shaped surface forcing functions. Unlike in such experiments, topographically preconditioned chimneys are not prone to breakup by the growth of baroclinic instabilities. Instead, convection is generally shut down by horizontal fluxes of heat due to the mean flow across the temperature gradients of the chimney walls. The presence of the mean flow, which is neccessary in order for the topographic preconditioning to work, causes instabilities to be advected downstream faster than they can grow locally. These results suggest that the role of baroclinic eddies in shutting down oceanographic convection is probably misrepresented in studies which parameterize the preconditioning mechanism, particularly if the preconditioning mechanism being parameterized is a topographic one.en_US
dc.description.sponsorshipFinancial support for the thesis research was provided by NOAA grant number NA16RC0073 and NSF grant number OCE90-04864. Additional financial support was provided by the Office of Naval Research, Physical Oceanography Division under grant number N00014- 86-K-0751 as well as an AASERT fellowship, grant number N00014-89-J-1106.en_US
dc.format.mimetypeapplication/pdf
dc.language.isoen_USen_US
dc.publisherMassachusetts Institute of Technology and Woods Hole Oceanographic Institutionen_US
dc.relation.ispartofseriesWHOI Thesesen_US
dc.subjectSubmarine topographyen_US
dc.subjectConvectionen_US
dc.titleTopographic preconditioning of open ocean deep convectionen_US
dc.typeThesisen_US
dc.identifier.doi10.1575/1912/5618


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