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The Neutral Density Temporal Residual Mean overturning circulation

Stewart, A. L. and Thompson, A. F. (2015) The Neutral Density Temporal Residual Mean overturning circulation. Ocean Modelling, 90 . pp. 44-56. ISSN 1463-5003.

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Diagnosis of the ocean’s overturning circulation is essential to closing global budgets of heat, salt and biogeochemical tracers. This diagnosis is sensitive to the choice of density variable used to distinguish water masses and identify transformations between them. The oceanographic community has adopted neutral density for this purpose because its isopycnal slopes are approximately aligned with neutral slopes, along which ocean flows tend to be confined. At high latitudes there are often no tenable alternatives because potential density varies non-monotonically with depth, regardless of the reference pressure. However, in many applications the use of isoneutral fluxes is impractical due to the high computational cost of calculating neutral density. Consequently neutral density-related diagnostics are typically not available as output from ocean models. In this article the authors derive a modified Temporal Residual Mean (TRM) approximation to the isoneutral mass fluxes, referred to as the Neutral Density Temporal Residual Mean (NDTRM). The NDTRM may be calculated using quantities that are routinely offered as diagnostic output from ocean models, making it several orders of magnitude faster than explicitly computing isoneutral mass fluxes. The NDTRM is assessed using a process model of the Antarctic continental shelf and slope. The onshore transport of warm Circumpolar Deep Water in the model ocean interior approximately doubles when diagnosed using neutral density, rather than potential density. The NDTRM closely approximates these explicitly-computed isoneutral mass fluxes. The NDTRM also exhibits a much smaller error than the traditional TRM in regions of large isoneutral temperature and salinity gradients, where nonlinearities in the equation of state diabatically modify the neutral density.

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Thompson, A. F.0000-0003-0322-4811
Additional Information:© 2015 Elsevier Ltd. Received 19 September 2014; Revised 23 March 2015; Accepted 25 March 2015; Available online 02 April 2015. A.L.S.’s and A.F.T.’s work was carried out at the California Institute of Technology under a contract with the National Aeronautics and Space Administration and funded through the President’s and Director’s Fund Program. The simulations presented herein were conducted using the CITerra computing cluster in the Division of Geological and Planetary Sciences at the California Institute of Technology, and the authors thank the CITerra technicians for facilitating this work. The authors gratefully acknowledge the modeling efforts of the MITgcm team. The authors thank Trevor McDougall and another anonymous reviewer for insightful comments that improved the manuscript.
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Subject Keywords:Transformed residual mean; Neutral density; Ocean overturning; Antarctic circulation
Record Number:CaltechAUTHORS:20150618-104551443
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Official Citation:A.L. Stewart, A.F. Thompson, The Neutral Density Temporal Residual Mean overturning circulation, Ocean Modelling, Volume 90, June 2015, Pages 44-56, ISSN 1463-5003, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:58344
Deposited By: Tony Diaz
Deposited On:19 Jun 2015 01:08
Last Modified:26 Sep 2017 22:16

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