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Determining Thorpe Scales from Ship-Lowered CTD Density Profiles

Determining Thorpe Scales from Ship-Lowered CTD Density Profiles CTD measurements taken as an integral part of oceanographic cruises could provide valuable information on spatial locations and time variability of significant shear-generated mixing in the ocean interior if used routinely to calculate Thorpe scales, that is, estimates of the scales of vertical overturning in an otherwise stably stratified fluid. This paper outlines methods for calculating reliable Thorpe scales from density profiles taken with a shipborne CTD, including removal of questionable instabilities associated with termination of pressure reversals, reduction of the effects of density noise by computation of an intermediate density profile, and overturn verification by a two-parameter ( R o , ΔΔ N ) diagnostic. The R o criterion alone reliably removes overturns that result from salinity spikes at the high gradient boundaries of a weakly stratified layer, a common cause of highly suspect overturns. The ΔΔ N diagnostic is a new water mass test describing the degree of ““tightness”” of the temperature––salinity ( T –– S ) relationship. The present two-parameter diagnostic rejects a significantly larger percentage of suspect overturns than does a previous single-parameter water mass test. Despite developing a more reliable water mass diagnostic, the authors conclude that rejection of overturns based on a water mass test that incorporates expectation of T –– S tightness is not warranted, given possibilities of T –– S ““looseness”” resulting from mixing over regions of nonlinear T –– S structure and/or from potential effects of differential diffusion. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Atmospheric and Oceanic Technology American Meteorological Society

Determining Thorpe Scales from Ship-Lowered CTD Density Profiles

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References (20)

Publisher
American Meteorological Society
Copyright
Copyright © 2006 American Meteorological Society
ISSN
1520-0426
DOI
10.1175/2008JTECHO541.1
Publisher site
See Article on Publisher Site

Abstract

CTD measurements taken as an integral part of oceanographic cruises could provide valuable information on spatial locations and time variability of significant shear-generated mixing in the ocean interior if used routinely to calculate Thorpe scales, that is, estimates of the scales of vertical overturning in an otherwise stably stratified fluid. This paper outlines methods for calculating reliable Thorpe scales from density profiles taken with a shipborne CTD, including removal of questionable instabilities associated with termination of pressure reversals, reduction of the effects of density noise by computation of an intermediate density profile, and overturn verification by a two-parameter ( R o , ΔΔ N ) diagnostic. The R o criterion alone reliably removes overturns that result from salinity spikes at the high gradient boundaries of a weakly stratified layer, a common cause of highly suspect overturns. The ΔΔ N diagnostic is a new water mass test describing the degree of ““tightness”” of the temperature––salinity ( T –– S ) relationship. The present two-parameter diagnostic rejects a significantly larger percentage of suspect overturns than does a previous single-parameter water mass test. Despite developing a more reliable water mass diagnostic, the authors conclude that rejection of overturns based on a water mass test that incorporates expectation of T –– S tightness is not warranted, given possibilities of T –– S ““looseness”” resulting from mixing over regions of nonlinear T –– S structure and/or from potential effects of differential diffusion.

Journal

Journal of Atmospheric and Oceanic Technology – American Meteorological Society

Published: Nov 8, 2006

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