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Effective Eddy Diffusivities Inferred from a Point Release Tracer in an Eddy-Resolving Ocean Model

Effective Eddy Diffusivities Inferred from a Point Release Tracer in an Eddy-Resolving Ocean Model
Effective Eddy Diffusivities Inferred from a Point Release Tracer in an Eddy-Resolving Ocean Model
This study uses tracer experiments in a global eddy-resolving ocean model to examine two diagnostic methods for inferring effective eddy isopycnic diffusivity from point release tracers. The first method is based on the growth rate of the area occupied by the tracers (the equivalent variance). During the period when tracer dispersion is dominated by stirring, the equivalent variance is found to increase at a rate between the second power law (for a pure shearing flow regime) and the exponential law (for a pure stretching flow regime). The second method is based on the length of the tracer contours. In the framework of equivalent radius, the two methods of inferring eddy diffusivity can be understood as two different averagings over the tracer patch. Over a shorter period of tracer dispersion the two methods give different eddy diffusivities, and only over a longer time when tracer dispersion approaches the final stage of diffusion do they give a similar value of diffusivity. A new diagnostic quantity called stirring efficiency is introduced to indicate different flow regimes by measuring the efficiency of stirring against mixing. The new diagnostic quantity has the advantage that it can be calculated directly from the gradients of tracer distribution without needing to estimate strain rate or background diffusivity.
0022-3670
894-914
Lee, Mei-Man
59401716-3903-401c-96de-d758970eeb03
Nurser, A.J. George
2493ef9a-21e9-4d8b-9c32-08677e7e145a
Coward, Andrew C.
53b78140-2e65-476a-b287-e8384a65224b
de Cuevas, Beverly A.
01cc697c-2832-4de6-87bf-bf9f16c1f906
Lee, Mei-Man
59401716-3903-401c-96de-d758970eeb03
Nurser, A.J. George
2493ef9a-21e9-4d8b-9c32-08677e7e145a
Coward, Andrew C.
53b78140-2e65-476a-b287-e8384a65224b
de Cuevas, Beverly A.
01cc697c-2832-4de6-87bf-bf9f16c1f906

Lee, Mei-Man, Nurser, A.J. George, Coward, Andrew C. and de Cuevas, Beverly A. (2009) Effective Eddy Diffusivities Inferred from a Point Release Tracer in an Eddy-Resolving Ocean Model. Journal of Physical Oceanography, 39 (4), 894-914. (doi:10.1175/2008JPO3902.1).

Record type: Article

Abstract

This study uses tracer experiments in a global eddy-resolving ocean model to examine two diagnostic methods for inferring effective eddy isopycnic diffusivity from point release tracers. The first method is based on the growth rate of the area occupied by the tracers (the equivalent variance). During the period when tracer dispersion is dominated by stirring, the equivalent variance is found to increase at a rate between the second power law (for a pure shearing flow regime) and the exponential law (for a pure stretching flow regime). The second method is based on the length of the tracer contours. In the framework of equivalent radius, the two methods of inferring eddy diffusivity can be understood as two different averagings over the tracer patch. Over a shorter period of tracer dispersion the two methods give different eddy diffusivities, and only over a longer time when tracer dispersion approaches the final stage of diffusion do they give a similar value of diffusivity. A new diagnostic quantity called stirring efficiency is introduced to indicate different flow regimes by measuring the efficiency of stirring against mixing. The new diagnostic quantity has the advantage that it can be calculated directly from the gradients of tracer distribution without needing to estimate strain rate or background diffusivity.

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Published date: April 2009

Identifiers

Local EPrints ID: 66243
URI: http://eprints.soton.ac.uk/id/eprint/66243
ISSN: 0022-3670
PURE UUID: e700dade-4ae5-40ff-80aa-ec4ec4d38094

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Date deposited: 18 May 2009
Last modified: 13 Mar 2024 18:12

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Contributors

Author: Mei-Man Lee
Author: A.J. George Nurser
Author: Andrew C. Coward
Author: Beverly A. de Cuevas

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