Publication Abstracts

Canuto et al. 2011

Canuto, V.M., Y. Cheng, and A.M. Howard, 2011: Vertical diffusivities of active and passive tracers. Ocean Model., 36, 198-207, doi:10.1016/j.ocemod.2010.12.002.

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, δT/δz > 0, δS/δz < 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, δT/δz < 0, δS/δz < 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, δT/δz > 0, δS/δz > 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.

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BibTeX Citation

@article{ca04320y,
  author={Canuto, V. M. and Cheng, Y. and Howard, A. M.},
  title={Vertical diffusivities of active and passive tracers},
  year={2011},
  journal={Ocean Model.},
  volume={36},
  pages={198--207},
  doi={10.1016/j.ocemod.2010.12.002},
}

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RIS Citation

TY  - JOUR
ID  - ca04320y
AU  - Canuto, V. M.
AU  - Cheng, Y.
AU  - Howard, A. M.
PY  - 2011
TI  - Vertical diffusivities of active and passive tracers
JA  - Ocean Model.
VL  - 36
SP  - 198
EP  - 207
DO  - 10.1016/j.ocemod.2010.12.002
ER  -

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