The role of mixed-layer instabilities in submesoscale turbulence
Upper-ocean turbulence at scales smaller than the mesoscale is believed to exchange surface and thermocline waters, which plays an important role in both physical and biogeochemical budgets. But what energizes this submesoscale turbulence remains a topic of debate. Two mechanisms have been proposed:...
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Cambridge University Press (CUP)
2018
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| Online Access: | http://hdl.handle.net/1721.1/116612 https://orcid.org/0000-0002-2278-2811 https://orcid.org/0000-0003-3589-5249 https://orcid.org/0000-0002-3736-1956 https://orcid.org/0000-0002-2871-2048 |
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| author | Callies, Joern Flierl, Glenn Richard Ferrari, Raffaele Fox-Kemper, Baylor |
| author2 | Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences |
| author_facet | Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences Callies, Joern Flierl, Glenn Richard Ferrari, Raffaele Fox-Kemper, Baylor |
| author_sort | Callies, Joern |
| collection | MIT |
| description | Upper-ocean turbulence at scales smaller than the mesoscale is believed to exchange surface and thermocline waters, which plays an important role in both physical and biogeochemical budgets. But what energizes this submesoscale turbulence remains a topic of debate. Two mechanisms have been proposed: mesoscale-driven surface frontogenesis and baroclinic mixed-layer instabilities. The goal here is to understand the differences between the dynamics of these two mechanisms, using a simple quasi-geostrophic model. The essence of mesoscale-driven surface frontogenesis is captured by the well-known surface quasi-geostrophic model, which describes the sharpening of surface buoyancy gradients and the subsequent breakup in secondary roll-up instabilities. We formulate a similarly archetypical Eady-like model of submesoscale turbulence induced by mixed-layer instabilities. The model captures the scale and structure of this baroclinic instability in the mixed layer. A wide range of scales are energized through a turbulent inverse cascade of kinetic energy that is fuelled by the submesoscale mixed-layer instability. Major differences to mesoscale-driven surface frontogenesis are that mixed-layer instabilities energize the entire depth of the mixed layer and produce larger vertical velocities. The distribution of energy across scales and in the vertical produced by our simple model of mixed-layer instabilities compares favourably to observations of energetic wintertime submesoscale flows, suggesting that it captures the leading-order balanced dynamics of these flows. The dynamics described here in an oceanographic context have potential applications to other geophysical fluids with layers of different stratifications. |
| first_indexed | 2024-09-23T11:41:10Z |
| format | Article |
| id | mit-1721.1/116612 |
| institution | Massachusetts Institute of Technology |
| last_indexed | 2024-09-23T11:41:10Z |
| publishDate | 2018 |
| publisher | Cambridge University Press (CUP) |
| record_format | dspace |
| spelling | mit-1721.1/1166122022-10-01T05:16:15Z The role of mixed-layer instabilities in submesoscale turbulence Callies, Joern Flierl, Glenn Richard Ferrari, Raffaele Fox-Kemper, Baylor Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences Callies, Joern Flierl, Glenn Richard Ferrari, Raffaele Fox-Kemper, Baylor Upper-ocean turbulence at scales smaller than the mesoscale is believed to exchange surface and thermocline waters, which plays an important role in both physical and biogeochemical budgets. But what energizes this submesoscale turbulence remains a topic of debate. Two mechanisms have been proposed: mesoscale-driven surface frontogenesis and baroclinic mixed-layer instabilities. The goal here is to understand the differences between the dynamics of these two mechanisms, using a simple quasi-geostrophic model. The essence of mesoscale-driven surface frontogenesis is captured by the well-known surface quasi-geostrophic model, which describes the sharpening of surface buoyancy gradients and the subsequent breakup in secondary roll-up instabilities. We formulate a similarly archetypical Eady-like model of submesoscale turbulence induced by mixed-layer instabilities. The model captures the scale and structure of this baroclinic instability in the mixed layer. A wide range of scales are energized through a turbulent inverse cascade of kinetic energy that is fuelled by the submesoscale mixed-layer instability. Major differences to mesoscale-driven surface frontogenesis are that mixed-layer instabilities energize the entire depth of the mixed layer and produce larger vertical velocities. The distribution of energy across scales and in the vertical produced by our simple model of mixed-layer instabilities compares favourably to observations of energetic wintertime submesoscale flows, suggesting that it captures the leading-order balanced dynamics of these flows. The dynamics described here in an oceanographic context have potential applications to other geophysical fluids with layers of different stratifications. 2018-06-26T14:26:23Z 2018-06-26T14:26:23Z 2015-12 2018-06-26T12:42:00Z Article http://purl.org/eprint/type/JournalArticle 0022-1120 1469-7645 http://hdl.handle.net/1721.1/116612 Callies, Jörn, Glenn Flierl, Raffaele Ferrari, and Baylor Fox-Kemper. “The Role of Mixed-Layer Instabilities in Submesoscale Turbulence.” Journal of Fluid Mechanics 788 (December 2015): 5–41 © 2016 Cambridge University Press https://orcid.org/0000-0002-2278-2811 https://orcid.org/0000-0003-3589-5249 https://orcid.org/0000-0002-3736-1956 https://orcid.org/0000-0002-2871-2048 http://dx.doi.org/10.1017/JFM.2015.700 Journal of Fluid Mechanics Creative Commons Attribution-Noncommercial-Share Alike http://creativecommons.org/licenses/by-nc-sa/4.0/ application/pdf Cambridge University Press (CUP) Prof. Ferrari via Chris Sherratt |
| spellingShingle | Callies, Joern Flierl, Glenn Richard Ferrari, Raffaele Fox-Kemper, Baylor The role of mixed-layer instabilities in submesoscale turbulence |
| title | The role of mixed-layer instabilities in submesoscale turbulence |
| title_full | The role of mixed-layer instabilities in submesoscale turbulence |
| title_fullStr | The role of mixed-layer instabilities in submesoscale turbulence |
| title_full_unstemmed | The role of mixed-layer instabilities in submesoscale turbulence |
| title_short | The role of mixed-layer instabilities in submesoscale turbulence |
| title_sort | role of mixed layer instabilities in submesoscale turbulence |
| url | http://hdl.handle.net/1721.1/116612 https://orcid.org/0000-0002-2278-2811 https://orcid.org/0000-0003-3589-5249 https://orcid.org/0000-0002-3736-1956 https://orcid.org/0000-0002-2871-2048 |
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