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Irreversible Fluxes in Double-Diffusive Systems and the Origin of Thermohaline Staircases.

Record Type:	Electronic resources : Monograph/item
Title/Author:	Irreversible Fluxes in Double-Diffusive Systems and the Origin of Thermohaline Staircases./
Author:	Ma, Yuchen.
Description:	1 online resource (180 pages)
Notes:	Source: Dissertations Abstracts International, Volume: 84-09, Section: B.
Contained By:	Dissertations Abstracts International84-09B.
Subject:	Physical oceanography. -
Online resource:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=30246578click for full text (PQDT)
ISBN:	9798377616436

Irreversible Fluxes in Double-Diffusive Systems and the Origin of Thermohaline Staircases.
Ma, Yuchen.

Irreversible Fluxes in Double-Diffusive Systems and the Origin of Thermohaline Staircases. - 1 online resource (180 pages)

Source: Dissertations Abstracts International, Volume: 84-09, Section: B.

Thesis (Ph.D.)--University of Toronto (Canada), 2023.

Includes bibliographical references

Thermohaline staircases are structures in the ocean characterized by well-mixed layers of uniform temperature and salinity separated by sharp interfaces. Based on the background stratifications in which these structures are embedded, observed staircases can be categorized into salt-fingering and diffusive-convection staircases. Although it is generally believed that the formation of these staircase structures is related to double-diffusive processes, a detailed formation mechanism is still under debate, especially for those found in the Arctic Ocean. In this thesis, I have systematically investigated the formation of both types of staircases, those found in the low-latitude oceans and those found in the polar oceans. This investigation is pursued by studying the flux laws that govern the turbulent environment in each of these regimes. Specifically, I first developed a theoretical framework that can be used to separate the irreversible component of turbulent mixing from the reversible stirring component in a double-diffusive system. Direct numerical simulations were then performed in both the salt-fingering system and the shear-driven diffusive-convection system in order to infer accurate parameterization schemes that best capture these systems' irreversible fluxes. These flux parameterizations were further analyzed theoretically to understand the mechanism for the development of the staircase structures. For the salt-fingering system, I studied the evolution of salt-fingering staircases in a vertically inhomogeneous environment and addressed the observational trend that the characteristic step size in a salt-fingering staircase is larger in regions characterized by weaker gradients. For the diffusive-convection system, I systematically investigated an original mechanism that appears to be responsible for the formation of thermohaline staircase structures that broadly exist in the Arctic Ocean, which has puzzled researchers for five decades. This work shows that a stratified-turbulence-based layering mechanism could be responsible for the layer formation process in the Arctic pycnocline. Contrary to conventional wisdom, double diffusion based upon the different molecular diffusivities of heat and salt plays no significant role in staircase formation in the diffusive-convection regime. Rather, in this regime, the control on layer formation is provided by the turbulent diffusivities of heat and salt.

Electronic reproduction.
Ann Arbor, Mich. :
ProQuest,
2023

Mode of access: World Wide Web

ISBN: 9798377616436Subjects--Topical Terms:

3168433
Physical oceanography.
Subjects--Index Terms:

Thermohaline staircasesIndex Terms--Genre/Form:

542853
Electronic books.

Irreversible Fluxes in Double-Diffusive Systems and the Origin of Thermohaline Staircases.
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520 $a Thermohaline staircases are structures in the ocean characterized by well-mixed layers of uniform temperature and salinity separated by sharp interfaces. Based on the background stratifications in which these structures are embedded, observed staircases can be categorized into salt-fingering and diffusive-convection staircases. Although it is generally believed that the formation of these staircase structures is related to double-diffusive processes, a detailed formation mechanism is still under debate, especially for those found in the Arctic Ocean. In this thesis, I have systematically investigated the formation of both types of staircases, those found in the low-latitude oceans and those found in the polar oceans. This investigation is pursued by studying the flux laws that govern the turbulent environment in each of these regimes. Specifically, I first developed a theoretical framework that can be used to separate the irreversible component of turbulent mixing from the reversible stirring component in a double-diffusive system. Direct numerical simulations were then performed in both the salt-fingering system and the shear-driven diffusive-convection system in order to infer accurate parameterization schemes that best capture these systems' irreversible fluxes. These flux parameterizations were further analyzed theoretically to understand the mechanism for the development of the staircase structures. For the salt-fingering system, I studied the evolution of salt-fingering staircases in a vertically inhomogeneous environment and addressed the observational trend that the characteristic step size in a salt-fingering staircase is larger in regions characterized by weaker gradients. For the diffusive-convection system, I systematically investigated an original mechanism that appears to be responsible for the formation of thermohaline staircase structures that broadly exist in the Arctic Ocean, which has puzzled researchers for five decades. This work shows that a stratified-turbulence-based layering mechanism could be responsible for the layer formation process in the Arctic pycnocline. Contrary to conventional wisdom, double diffusion based upon the different molecular diffusivities of heat and salt plays no significant role in staircase formation in the diffusive-convection regime. Rather, in this regime, the control on layer formation is provided by the turbulent diffusivities of heat and salt.
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