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Idealized Oceanic Lee Waves: Theory ...

Mayer, Frederick T.

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Idealized Oceanic Lee Waves: Theory and Numerical Experiments of Ocean Currents Flowing over Sinusoidal Bathymetry.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	Idealized Oceanic Lee Waves: Theory and Numerical Experiments of Ocean Currents Flowing over Sinusoidal Bathymetry./
作者:	Mayer, Frederick T.
出版者:	Ann Arbor : ProQuest Dissertations & Theses, : 2020,
面頁冊數:	209 p.
附註:	Source: Dissertations Abstracts International, Volume: 82-02, Section: B.
Contained By:	Dissertations Abstracts International82-02B.
標題:	Geophysics. -
電子資源:	https://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=28103991
ISBN:	9798662510777

Idealized Oceanic Lee Waves: Theory and Numerical Experiments of Ocean Currents Flowing over Sinusoidal Bathymetry.
Mayer, Frederick T.

Idealized Oceanic Lee Waves: Theory and Numerical Experiments of Ocean Currents Flowing over Sinusoidal Bathymetry. - Ann Arbor : ProQuest Dissertations & Theses, 2020 - 209 p.

Source: Dissertations Abstracts International, Volume: 82-02, Section: B.

Thesis (Ph.D.)--Stanford University, 2020.

This item must not be sold to any third party vendors.

When a relatively steady ocean current flows over a hill or train of hills on the ocean floor, it excites vertical oscillations, or internal gravity waves, known as lee waves. Because there are hills throughout the deep ocean, lee waves are likely a ubiquitous feature of ocean currents. However, they occur on length scales that are smaller than the grid-scale of Global Circulation Models. GCMs must therefore parameterize the drag associated with launching lee waves. Existing parameterizations were developed for weather models to predict the drag caused by atmospheric lee waves above mountains. To assess the suitability of employing atmospheric parameterizations in the deep ocean, this dissertation presents theory and numerical simulations of an idealized lee wave representative of oceanic conditions. By nondimensionalizing the governing steady-state equations, this dissertation provides a rigorous definition of the oceanic lee wave parameter space, and resolves a longstanding dispute in the literature over the definition of the lee wave Froude number. The exercise also permits a derivation of the nonhydrostatic linear lee wave drag in nondimensional form. However, many abyssal hills are not linear, meaning the lee waves they launch likely exhibit dynamics not captured by linear theory. Hence this dissertation presents high-resolution nonhydrostatic lee wave simulations spanning the parameter space. These simulations afford a time-varying glimpse at the spin up of oceanic lee waves and identify a characteristic timescale to reach steady state. In steady state, the simulations offer the opportunity to test the saturation hypothesis currently employed in GCMs, whereby it is assumed that hills taller than some critical height will squeeze all of the wave making capacity out of the currents, causing the wave drag to saturate at a known magnitude. Because this hypothesis employs only the height of the hills, it implicitly assumes that saturation is a hydrostatic process. While this may be appropriate in the atmosphere, the simulations identify a set of nonhydrostatic features of oceanic lee wave saturation that can result in dramatic reductions of the drag. This dissertation thus implies that GCMs might grossly overpredict the lee wave drag in the ocean.

ISBN: 9798662510777Subjects--Topical Terms:

535228
Geophysics.
Subjects--Index Terms:

Lee waves

Idealized Oceanic Lee Waves: Theory and Numerical Experiments of Ocean Currents Flowing over Sinusoidal Bathymetry.
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520 $a When a relatively steady ocean current flows over a hill or train of hills on the ocean floor, it excites vertical oscillations, or internal gravity waves, known as lee waves. Because there are hills throughout the deep ocean, lee waves are likely a ubiquitous feature of ocean currents. However, they occur on length scales that are smaller than the grid-scale of Global Circulation Models. GCMs must therefore parameterize the drag associated with launching lee waves. Existing parameterizations were developed for weather models to predict the drag caused by atmospheric lee waves above mountains. To assess the suitability of employing atmospheric parameterizations in the deep ocean, this dissertation presents theory and numerical simulations of an idealized lee wave representative of oceanic conditions. By nondimensionalizing the governing steady-state equations, this dissertation provides a rigorous definition of the oceanic lee wave parameter space, and resolves a longstanding dispute in the literature over the definition of the lee wave Froude number. The exercise also permits a derivation of the nonhydrostatic linear lee wave drag in nondimensional form. However, many abyssal hills are not linear, meaning the lee waves they launch likely exhibit dynamics not captured by linear theory. Hence this dissertation presents high-resolution nonhydrostatic lee wave simulations spanning the parameter space. These simulations afford a time-varying glimpse at the spin up of oceanic lee waves and identify a characteristic timescale to reach steady state. In steady state, the simulations offer the opportunity to test the saturation hypothesis currently employed in GCMs, whereby it is assumed that hills taller than some critical height will squeeze all of the wave making capacity out of the currents, causing the wave drag to saturate at a known magnitude. Because this hypothesis employs only the height of the hills, it implicitly assumes that saturation is a hydrostatic process. While this may be appropriate in the atmosphere, the simulations identify a set of nonhydrostatic features of oceanic lee wave saturation that can result in dramatic reductions of the drag. This dissertation thus implies that GCMs might grossly overpredict the lee wave drag in the ocean.
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