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Eddy Dynamics of Eastern Boundary Currents
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| 자료유형 | 학위논문 |
|---|---|
| 서명/저자사항 | Eddy Dynamics of Eastern Boundary Currents. |
| 개인저자 | Bire, Suyash Ulhas. |
| 단체저자명 | State University of New York at Stony Brook. Marine and Atmospheric Science. |
| 발행사항 | [S.l.]: State University of New York at Stony Brook., 2019. |
| 발행사항 | Ann Arbor: ProQuest Dissertations & Theses, 2019. |
| 형태사항 | 133 p. |
| 기본자료 저록 | Dissertations Abstracts International 81-04B. Dissertation Abstract International |
| ISBN | 9781687962713 |
| 학위논문주기 | Thesis (Ph.D.)--State University of New York at Stony Brook, 2019. |
| 일반주기 |
Source: Dissertations Abstracts International, Volume: 81-04, Section: B.
Advisor: Wolfe, Christopher L P. |
| 이용제한사항 | This item must not be sold to any third party vendors.This item must not be added to any third party search indexes. |
| 요약 | Most oceanic eastern boundaries are characterized by a surface equatorward current and a poleward undercurrent.The Leeuwin current and the Iberian Poleward Current are exceptions---they flow poleward at the surface and equatorward below it.The large-scale equator-to-pole buoyancy gradient drives an eastward flow and accumulates water at the eastern boundary setting up a zonal pressure gradient which drives a poleward surface current.Equatorward winds force an offshore Ekman drift, creating an opposing zonal pressure gradient that drives an equatorward surface current.It is hypothesized that distinct eastern boundary systems arise due to the competition between upwelling-favorable equatorward winds and the downwelling-favorable buoyancy forcing.In this thesis, this hypothesis is tested by means of a series of eddy-resolving numerical simulations in rectangular basins.An additional goal of this thesis is to determine the dynamics responsible for trapping narrow eastern boundary currents (EBCs). Previous studies have proposed topography, wind, and enhanced diapycnal mixing as trapping mechanisms, but eddy-resolving simulations including none of these effects still produce trapped EBCs.It is demonstrated that mesoscale eddies play an essential role in EBC trapping.The purely buoyancy-forced case without bottom topography is considered first.It is shown that buoyancy advection in the EBC is primarily balanced by the shedding of eddies, with anticyclonic, warm-core eddies dominating.The efficiency of the eddy interfacial form drag increases dramatically at the offshore flank of the EBC.This zonal variation of the form drag is essential for maintaining a swift, narrow EBC, which is poleward at the surface and equatorward at intermediate depths.Additionally, it is shown that while downwelling is restricted to a very narrow layer near the eastern boundary, this downwelling is nearly adiabatic and spatial scale for diapycnal transformations is that of the basin itself.Thus, the eddies shed from the EBC play a significant role in both the eastern boundary circulation---by helping to trap the EBC near the coast---and the large-scale circulation through their effect on the downwelling limb of the overturning circulation.The sensitivity of the trapping mechanism outlined above is assessed by adding cross-shore topographic variations and along-shore wind forcing.It is observed that the interfacial form drag begins to intensify on the continental slope, where the buoyancy-forced poleward current is trapped, and attains its maximum efficiency offshore of the continental slope.In the presence of topography the flow has a tendency to follow contours of constant planetary potential vorticity except where the bottom pressure torques are significant.Hence, in the case with topography but without wind, a significant portion of the transport by the poleward EBC returns southward by traversing the northern and western boundaries instead of downwelling at the eastern boundary.As a result, the deep equatorward current along the eastern boundary becomes weaker than in the case without topography.In the absence of topographic variations, even very strong equatorward winds are unable to overcome the poleward current at the surface.The presence of a realistic topography, however, favors the action of wind over that of buoyancy.In this case, the equatorward current is present onshore of the shelf break, while the poleward current is pushed offshore and deeper along the continental slope.An additional layer of equatorward currents is seen below the poleward current on the continental slope.Thus, both realistic topography and equatorward winds are required to produce a wind-forced equator-ward surface current on top of the buoyancy-driven poleward current. |
| 일반주제명 | Physical oceanography. |
| 언어 | 영어 |
| 바로가기 | 
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