Vertical Diffusivities of Active and Passive Tracers
The climate models that include a carbon-cycle need the vertical diffusivity of a passive tracer. Since an expression for the latter is not available, it has been common practice to identify it with that of salt. The identification is questionable since T, S are active, not passive tracers. We prese...
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ftnasantrs:oai:casi.ntrs.nasa.gov:20120010489 2023-05-15T17:35:48+02:00 Vertical Diffusivities of Active and Passive Tracers Cheng, Y. Howard, A. M. Canuto, V. M. Unclassified, Unlimited, Publicly available December 15, 2010 application/pdf http://hdl.handle.net/2060/20120010489 unknown Document ID: 20120010489 http://hdl.handle.net/2060/20120010489 Copyright, Distribution as joint owner in the copyright CASI Geophysics GSFC.JA.00359.2012 Ocean Modelling; 36; 4-Mar; 198-207 2010 ftnasantrs 2019-07-21T00:49:55Z The climate models that include a carbon-cycle need the vertical diffusivity of a passive tracer. Since an expression for the latter is not available, it has been common practice to identify it with that of salt. The identification is questionable since T, S are active, not passive tracers. We present the first derivation of the diffusivity of a passive tracer in terms of Ri (Richardson number) and Rq (density ratio, ratio of salinity over temperature z-gradients). The following results have emerged: (a) The passive tracer diffusivity is an algebraic function of Ri, Rq. (b) In doubly stable regimes (DS, partial derivative of T with respect to z > 0, partial derivative of S with respect to z < 0), the passive scalar diffusivity is nearly the same as that of salt/heat for any values of Rq < 0 and Ri > 0. (c) In DC regimes (diffusive convection, partial derivative of T with respect to z < 0, partial derivative of S with respect to z < 0, Rq > 1), the passive scalar diffusivity is larger than that of salt. At Ri = O(1), it can be more than twice as large. (d) In SF regimes (salt fingers, partial derivative of T with respect to z > 0, partial derivative of S with respect to z > 0, Rq < 1), the passive scalar diffusivity is smaller than that of salt. At Ri = O(1), it can be less than half of it. (e) The passive tracer diffusivity predicted at the location of NATRE (North Atlantic Tracer Release Experiment) is discussed. (f) Perhaps the most relevant conclusion is that the common identification of the tracer diffusivity with that of salt is valid only in DS regimes. In the Southern Ocean, where there is the largest CO2 absorption, the dominant regime is diffusive convection discussed in (c) above. Other/Unknown Material North Atlantic Southern Ocean NASA Technical Reports Server (NTRS) Southern Ocean |
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NASA Technical Reports Server (NTRS) |
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Geophysics |
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Geophysics Cheng, Y. Howard, A. M. Canuto, V. M. Vertical Diffusivities of Active and Passive Tracers |
topic_facet |
Geophysics |
description |
The climate models that include a carbon-cycle need the vertical diffusivity of a passive tracer. Since an expression for the latter is not available, it has been common practice to identify it with that of salt. The identification is questionable since T, S are active, not passive tracers. We present the first derivation of the diffusivity of a passive tracer in terms of Ri (Richardson number) and Rq (density ratio, ratio of salinity over temperature z-gradients). The following results have emerged: (a) The passive tracer diffusivity is an algebraic function of Ri, Rq. (b) In doubly stable regimes (DS, partial derivative of T with respect to z > 0, partial derivative of S with respect to z < 0), the passive scalar diffusivity is nearly the same as that of salt/heat for any values of Rq < 0 and Ri > 0. (c) In DC regimes (diffusive convection, partial derivative of T with respect to z < 0, partial derivative of S with respect to z < 0, Rq > 1), the passive scalar diffusivity is larger than that of salt. At Ri = O(1), it can be more than twice as large. (d) In SF regimes (salt fingers, partial derivative of T with respect to z > 0, partial derivative of S with respect to z > 0, Rq < 1), the passive scalar diffusivity is smaller than that of salt. At Ri = O(1), it can be less than half of it. (e) The passive tracer diffusivity predicted at the location of NATRE (North Atlantic Tracer Release Experiment) is discussed. (f) Perhaps the most relevant conclusion is that the common identification of the tracer diffusivity with that of salt is valid only in DS regimes. In the Southern Ocean, where there is the largest CO2 absorption, the dominant regime is diffusive convection discussed in (c) above. |
format |
Other/Unknown Material |
author |
Cheng, Y. Howard, A. M. Canuto, V. M. |
author_facet |
Cheng, Y. Howard, A. M. Canuto, V. M. |
author_sort |
Cheng, Y. |
title |
Vertical Diffusivities of Active and Passive Tracers |
title_short |
Vertical Diffusivities of Active and Passive Tracers |
title_full |
Vertical Diffusivities of Active and Passive Tracers |
title_fullStr |
Vertical Diffusivities of Active and Passive Tracers |
title_full_unstemmed |
Vertical Diffusivities of Active and Passive Tracers |
title_sort |
vertical diffusivities of active and passive tracers |
publishDate |
2010 |
url |
http://hdl.handle.net/2060/20120010489 |
op_coverage |
Unclassified, Unlimited, Publicly available |
geographic |
Southern Ocean |
geographic_facet |
Southern Ocean |
genre |
North Atlantic Southern Ocean |
genre_facet |
North Atlantic Southern Ocean |
op_source |
CASI |
op_relation |
Document ID: 20120010489 http://hdl.handle.net/2060/20120010489 |
op_rights |
Copyright, Distribution as joint owner in the copyright |
_version_ |
1766135082518577152 |