The evolution and breakdown of submesoscale instabilities
Ocean submesoscales are the subject of increasing focus in the oceanographic literature; with instrumentation now more capable of observing them in situ and numerical models now able to reach the resolution required to more fully capture them. Submesoscales are typified by horizontal spatial scales...
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ftdatacite:10.17863/cam.25162 2023-05-15T18:26:03+02:00 The evolution and breakdown of submesoscale instabilities Stamper, Megan Andrena 2018 https://dx.doi.org/10.17863/cam.25162 https://www.repository.cam.ac.uk/handle/1810/277822 en eng Apollo - University of Cambridge Repository https://www.rioxx.net/licenses/all-rights-reserved/ All Rights Reserved All rights reserved submesoscales oceanography fluid dynamics geophysical fluid dynamics simulations baroclinic instability symmetric instability mixed layer instabilities ocean dynamics Eady model linear stability analysis geostrophic balance applied mathematics Text Thesis article-journal ScholarlyArticle 2018 ftdatacite https://doi.org/10.17863/cam.25162 2021-11-05T12:55:41Z Ocean submesoscales are the subject of increasing focus in the oceanographic literature; with instrumentation now more capable of observing them in situ and numerical models now able to reach the resolution required to more fully capture them. Submesoscales are typified by horizontal spatial scales of O(1 − 10) km, vertical scales O(100) m and time-scales of O(1) day and are known to be associated with regions of high vertical velocity and vorticity. Occurring most commonly at density fronts at the ocean surface they can control mixed layer restratification and provide an important control on fluxes between the atmosphere and the deep ocean. This thesis sets out to better understand the fundamental physical processes underpinning submesoscale instabilities using a number of idealised process models. Linear stability analysis complemented by non-linear, high-resolution simulations will be used initially to explore the ways in which submesoscale instabilities in the mixed layer may compete and interact with one another. In particular, we will investigate the way in which symmetric and ageostrophic baroclinic instabilities interact when simultaneously present in a flow, with focus on the growth rates and energetic pathways of previously unexplored dynamic instabilities that arise in this paradigm; three-dimensional, mixed symmetric-baroclinic instabilities. Further, these non-linear simulations will allow us to investigate the transition to dissipative scales that can occur in the classical Eady model via a multitude of small-scale secondary instabilities that result from primary submesoscale instabilities. Finally, observational data, taken aboard the SMILES project cruise to the Southern Ocean, helps to motivate the consideration of a new dynamical paradigm; the Eady model with superimposed high amplitude barotropic jet. Non-linear simulations investigate the extent to which the addition of such a jet is capable of damping submesoscale growth. The causes of this damping are then investigated using linear analysis. With this approach eventually demonstrated as being unable to fully explain growth rate reductions, we introduce a new framework combining potential vorticity mixing by submesoscale instabilities with geostrophic adjustment, which relaxes the flow back to a geostrophic balanced state. This framework will help to explain, conceptually, how non-linear eddies control the linear stability of the flow. : PhD studentship funded as part of the Surface Mixed Layer at Submesoscales (SMILES) NERC grant NE/J010472/1 Thesis Southern Ocean DataCite Metadata Store (German National Library of Science and Technology) Southern Ocean |
institution |
Open Polar |
collection |
DataCite Metadata Store (German National Library of Science and Technology) |
op_collection_id |
ftdatacite |
language |
English |
topic |
submesoscales oceanography fluid dynamics geophysical fluid dynamics simulations baroclinic instability symmetric instability mixed layer instabilities ocean dynamics Eady model linear stability analysis geostrophic balance applied mathematics |
spellingShingle |
submesoscales oceanography fluid dynamics geophysical fluid dynamics simulations baroclinic instability symmetric instability mixed layer instabilities ocean dynamics Eady model linear stability analysis geostrophic balance applied mathematics Stamper, Megan Andrena The evolution and breakdown of submesoscale instabilities |
topic_facet |
submesoscales oceanography fluid dynamics geophysical fluid dynamics simulations baroclinic instability symmetric instability mixed layer instabilities ocean dynamics Eady model linear stability analysis geostrophic balance applied mathematics |
description |
Ocean submesoscales are the subject of increasing focus in the oceanographic literature; with instrumentation now more capable of observing them in situ and numerical models now able to reach the resolution required to more fully capture them. Submesoscales are typified by horizontal spatial scales of O(1 − 10) km, vertical scales O(100) m and time-scales of O(1) day and are known to be associated with regions of high vertical velocity and vorticity. Occurring most commonly at density fronts at the ocean surface they can control mixed layer restratification and provide an important control on fluxes between the atmosphere and the deep ocean. This thesis sets out to better understand the fundamental physical processes underpinning submesoscale instabilities using a number of idealised process models. Linear stability analysis complemented by non-linear, high-resolution simulations will be used initially to explore the ways in which submesoscale instabilities in the mixed layer may compete and interact with one another. In particular, we will investigate the way in which symmetric and ageostrophic baroclinic instabilities interact when simultaneously present in a flow, with focus on the growth rates and energetic pathways of previously unexplored dynamic instabilities that arise in this paradigm; three-dimensional, mixed symmetric-baroclinic instabilities. Further, these non-linear simulations will allow us to investigate the transition to dissipative scales that can occur in the classical Eady model via a multitude of small-scale secondary instabilities that result from primary submesoscale instabilities. Finally, observational data, taken aboard the SMILES project cruise to the Southern Ocean, helps to motivate the consideration of a new dynamical paradigm; the Eady model with superimposed high amplitude barotropic jet. Non-linear simulations investigate the extent to which the addition of such a jet is capable of damping submesoscale growth. The causes of this damping are then investigated using linear analysis. With this approach eventually demonstrated as being unable to fully explain growth rate reductions, we introduce a new framework combining potential vorticity mixing by submesoscale instabilities with geostrophic adjustment, which relaxes the flow back to a geostrophic balanced state. This framework will help to explain, conceptually, how non-linear eddies control the linear stability of the flow. : PhD studentship funded as part of the Surface Mixed Layer at Submesoscales (SMILES) NERC grant NE/J010472/1 |
format |
Thesis |
author |
Stamper, Megan Andrena |
author_facet |
Stamper, Megan Andrena |
author_sort |
Stamper, Megan Andrena |
title |
The evolution and breakdown of submesoscale instabilities |
title_short |
The evolution and breakdown of submesoscale instabilities |
title_full |
The evolution and breakdown of submesoscale instabilities |
title_fullStr |
The evolution and breakdown of submesoscale instabilities |
title_full_unstemmed |
The evolution and breakdown of submesoscale instabilities |
title_sort |
evolution and breakdown of submesoscale instabilities |
publisher |
Apollo - University of Cambridge Repository |
publishDate |
2018 |
url |
https://dx.doi.org/10.17863/cam.25162 https://www.repository.cam.ac.uk/handle/1810/277822 |
geographic |
Southern Ocean |
geographic_facet |
Southern Ocean |
genre |
Southern Ocean |
genre_facet |
Southern Ocean |
op_rights |
https://www.rioxx.net/licenses/all-rights-reserved/ All Rights Reserved All rights reserved |
op_doi |
https://doi.org/10.17863/cam.25162 |
_version_ |
1766207856085827584 |