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On the warm bias along the South-West African Coast in coupled models : an oceanic perspective (2008)

Wang, Jinbo

Massachusetts Institute of Technology and Woods Hole Oceanographic Institution

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Publikationsdatum: 2022-05-25

Beschreibung: Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2008

Beschreibung: Coupled ocean/atmosphere simulations exhibit systematicwarm biases over the SouthWest African (SWA) coastal region. Recent investigations indicate that coastal ocean dynamics may play an important role in determining the SST patterns, but none of them provide a detailed analysis. In this study, I analyze simulations produced both by coupled models and by idealized models. Then results are interpreted on the basis of a theoretical framework. Finally the conclusion is reached that the insufficient resolution of the ocean component in the coupled model is responsible for the warm biases over the SWA coastal region. The coarse resolution used in the ocean model has an artificially stretched coastal side-wall boundary layer, which induces a smaller upwelling velocity in the boundary layer. The vertical heat transport decreases even when the volume transport is unchanged because of its nonlinear relationship with the magnitude of the upwelling velocity. Based on the scaling of the idealized model simulations, a simplified calculation shows that the vertical heat transport is inversely proportional to the zonal resolution over the coastal region. Therefore, increasing the horizontal resolution can considerably improve the coastal SST simulation, and better resolve the coastal dynamics.

Schlagwort(e): Ocean-atmosphere interaction ; Computer simulation

Repository-Name: Woods Hole Open Access Server

Materialart: Thesis

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Instabilities of an eastern boundary current with and without large-scale flow influence (2011)

Wang, Jinbo

Massachusetts Institute of Technology and Woods Hole Oceanographic Institution

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Publikationsdatum: 2022-05-25

Beschreibung: 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 June 2011

Beschreibung: Eastern oceanic boundary currents are subject to hydrodynamic instability, generate small scale features that are visible in satellite images and may radiate westward into the interior, where they can be modified by the large-scale circulations. This thesis studies the stability of an eastern boundary current with and without the large-scale flow influence in an idealized framework represented by barotropic quasi-geostrophic dynamics. The linear stability analysis of a meridional current with a continuous velocity profile shows that meridional eastern and western boundary currents support a limited number of radiating modes with long meridional and zonal wavelengths and small growth rates. However, the linearly stable, long radiating modes of an eastern boundary current can become nonlinearly unstable by resonating with short trapped unstable modes. This phenomenon is clearly demonstrated in the weakly nonlinear simulations. Results suggest that linearly stable longwave modes deserve more attention when the radiating instability of a meridional boundary current is considered. A large-scale flow affects the short trapped unstable mode and long radiating mode through different mechanisms. The large-scale flow modifies the structure of the boundary current to stabilize or destabilize the unstable modes, leading to a meridionally localized maximum in the perturbation kinetic energy field. The shortwave mode is accelerated or decelerated by the meridional velocity adjustment of the large-scale flow to have an elongated or a squeezed meridional structure, which is confirmed both in a linear WKB analysis and in nonlinear simulations. The squeezed or elongated unstable mode detunes the nonlinear resonance with the longwave modes, which then become less energetic. These two modes show different meridional structures in kinetic energy field because of the different mechanisms. In spite of the model simplicity, these results can potentially explain the formation of the zonal jets observed in altimeter data, and indicate the influence of the large-scale wind-driven circulation on eastern boundary upwelling systems in the real ocean. Studies with more realistic configurations remain future challenges.

Schlagwort(e): Meridional overturning circulation ; Ocean circulation

Repository-Name: Woods Hole Open Access Server

Materialart: Thesis

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A new mechanism for the generation of quasi-zonal jets in the ocean (2012)

Wang, Jinbo ; Spall, Michael A. ; Flierl, Glenn R. ; [weitere]

American Geophysical Union

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Publikationsdatum: 2022-05-25

Beschreibung: Author Posting. © American Geophysical Union, 2012. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 39 (2012): L10601, doi:10.1029/2012GL051861.

Beschreibung: A simple barotropic quasi-geostrophic model is used to demonstrate that instabilities radiated from an unstable eastern boundary current can generate zonal striations in the ocean interior with realistic wavelengths and amplitudes. Nonlinear transfer of energy from the more unstable trapped modes is important for radiating modes to overcome friction. The dynamics shown here are generic enough to point to the eastern boundary current as a likely source of the observed striations extending from oceanic eastern boundaries.

Beschreibung: Y-S Fellowship when this study was done, and by NASA grant NNX12AD47G when this paper was prepared. M. Spall is supported by grant OCE-0926656. G. Flierl is supported by grant OCE-0752346.

Beschreibung: 2012-11-16

Schlagwort(e): Rossby waves ; Barotropic instability ; Eastern boundary currents ; Radiating instabilities ; Zonal jets ; Zonal striations

Repository-Name: Woods Hole Open Access Server

Materialart: Article

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