HR: 14:00h
AN: OS52L-01    [PDF]
TI: Plumes, Turbulent Entrainment and the Thermohaline Circulation of the Oceans
AU: * Hughes, G O
EM: graham.hughes@anu.edu.au
AF: Research School of Earth Sciences, The Australian National University, Canberra, ACT 0200 Australia
AU: Griffiths, R W
EM: ross.griffiths@anu.edu.au
AF: Research School of Earth Sciences, The Australian National University, Canberra, ACT 0200 Australia
AB: In a current view of ocean dynamics, the buoyancy forcing at the sea surface is insufficient to drive the estimated meridional overturning circulation (MOC). Energy budgets suggest that only the tides and the surface winds can provide enough energy to maintain the MOC, while heat stored in the relatively warm equatorial surface waters is advected passively poleward by the circulation. The observed density structure throughout much of the ocean volume is maintained by turbulent mixing that has been characterised by a vertical diffusivity of O(10$^{-4}$) m$^2$/s. However, numerous studies provide evidence supporting much smaller values for the diffusivity, of O(10$^{-5}$) m$^2$/s, in the ocean interior. Regions of very intense mixing at the boundaries and in the vicinity of rough topography raise the average vertical diffusivity, but this increase seems unlikely to be the required factor of ten. We have developed a `recycling box' model that prompts a new interpretation of existing data. When applied in the context of the global oceans using the observed values for the diffusivity in the interior, $\kappa = 10^{-5}$ m$^2$/s, and the poleward heat transport, the model predicts a vertical density structure in agreement with measured profiles. Forcing at the surface by buoyancy alone is shown to release sufficient energy to drive an active overturning circulation that maintains the density structure in the recycling box. The overturning circulation predicted by the model is a very significant fraction of that thought to occur in the oceans.
DE: 4203 Analytical modeling
DE: 4532 General circulation
DE: 4568 Turbulence, diffusion, and mixing processes
SC: Ocean Sciences [OS]
MN: 2004 Ocean Sciences Meeting