Eddy-induced mixed layer shallowing and mixed layer/thermocline exchange
Eddy-induced mixed layer shallowing and mixed layer/thermocline exchange
The effects of eddies on the mixed layer and on the transfer of properties between the mixed layer and thermocline are studied in a high-resolution model of an unstable front. A spring scenario is considered, with a mixed layer maintained against surface warming by wind mixing. Tilting of the buoyancy gradients by ageostrophic flow is found to shallow the mixed layer over the front, giving a mixed layer as shallow as 10 m in some places, compared with the equilibrium Monin-Obukhov depth of ~30 m away from the front. Variations of mixed layer depth with time and lateral advection lead to a subduction field that is substantially different from the vertical velocity field. Vertical velocities associated with the growing instabilities push tongues of a ventilation tracer, initially only present within the surface layer, down to depths of up to 100 m. After 24 days a quarter of this ventilation tracer has been deposited in the thermocline. Conversely, the vertical motions pull nutrients from the thermocline up into the mixed layer, giving enhanced surface values along the front. In the basin average the geostrophic eddies give vertical eddy diffusivities for a ventilation tracer of O (3 - 10 ×10-4m2s-1).
mixed layer, thermoclines, thermocline mixing, monin-obukov, geostrophic circulation
21851-21868
Nurser, A.J.G.
2493ef9a-21e9-4d8b-9c32-08677e7e145a
Zhang, J.W.
27009b1e-dd46-4a6c-a3bc-d5a90246d9e9
15 September 2000
Nurser, A.J.G.
2493ef9a-21e9-4d8b-9c32-08677e7e145a
Zhang, J.W.
27009b1e-dd46-4a6c-a3bc-d5a90246d9e9
Nurser, A.J.G. and Zhang, J.W.
(2000)
Eddy-induced mixed layer shallowing and mixed layer/thermocline exchange.
Journal of Geophysical Research, 105 (C9), .
(doi:10.1029/2000JC900018).
Abstract
The effects of eddies on the mixed layer and on the transfer of properties between the mixed layer and thermocline are studied in a high-resolution model of an unstable front. A spring scenario is considered, with a mixed layer maintained against surface warming by wind mixing. Tilting of the buoyancy gradients by ageostrophic flow is found to shallow the mixed layer over the front, giving a mixed layer as shallow as 10 m in some places, compared with the equilibrium Monin-Obukhov depth of ~30 m away from the front. Variations of mixed layer depth with time and lateral advection lead to a subduction field that is substantially different from the vertical velocity field. Vertical velocities associated with the growing instabilities push tongues of a ventilation tracer, initially only present within the surface layer, down to depths of up to 100 m. After 24 days a quarter of this ventilation tracer has been deposited in the thermocline. Conversely, the vertical motions pull nutrients from the thermocline up into the mixed layer, giving enhanced surface values along the front. In the basin average the geostrophic eddies give vertical eddy diffusivities for a ventilation tracer of O (3 - 10 ×10-4m2s-1).
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Published date: 15 September 2000
Keywords:
mixed layer, thermoclines, thermocline mixing, monin-obukov, geostrophic circulation
Identifiers
Local EPrints ID: 8746
URI: http://eprints.soton.ac.uk/id/eprint/8746
ISSN: 0148-0227
PURE UUID: 9572f6ec-7222-4e53-93e0-b0b06afe1cdb
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Date deposited: 14 Sep 2004
Last modified: 16 Mar 2024 02:53
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Author:
A.J.G. Nurser
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