In:
Journal of Fluid Mechanics, Cambridge University Press (CUP), Vol. 363 ( 1998-05-25), p. 229-252
Abstract:
Properties of the flow generated by a continuous source of dense
fluid on a slope in a rotating system are investigated with a variety of laboratory experiments.
The dense fluid may initially flow down the slope but it turns (under the influence
of rotation) to flow along the slope, and initial geostrophic adjustment gives it an anticyclonic
velocity profile. Some of the dense fluid drains downslope in a viscous Ekman layer,
which may become unstable to growing waves. Provided that the viscous draining is
not too strong, cyclonic vortices form periodically in the upper layer and the
dense flow breaks up into a series of domes. Three processes may contribute to the formation
of these eddies. First, initial downslope flow of the dense current may stretch
columns of ambient fluid by the ‘Taylor column’ process (which we
term ‘capture’). Secondly, the initial geostrophic adjustment implies lower-layer collapse which may stretch
the fluid column, and thirdly, viscous drainage will progressively stretch and spin
up a captured water column. Overall this last process may be the most significant, but
viscous drainage has contradictory effects, in that it progressively removes dense
lower-layer fluid which terminates the process when the layer thickness approaches
that of the Ekman layer. The eddies produced propagate along the slope owing to the
combined effects of buoyancy–Coriolis balance and ‘beta-gyres’. This removes fluid from the
vicinity of the source and causes the cycle to repeat. The vorticity of the upper-layer
cyclones increases linearly with Γ = L α/ D (where L is the Rossby deformation radius,
α the bottom slope and D the total depth), reaching
approximately 2 f in the
experiments presented here. The frequency at which the eddy/dome structures are
produced also increases with Γ , while the speed at
which the structures propagate along the slope is reduced by viscous effects. The flow of dense fluid on slopes
is a very important part of the global ocean circulation system and the implications
of the laboratory experiments for oceanographic flows are discussed.
Type of Medium:
Online Resource
ISSN:
0022-1120
,
1469-7645
DOI:
10.1017/S0022112098001013
Language:
English
Publisher:
Cambridge University Press (CUP)
Publication Date:
1998
detail.hit.zdb_id:
1472346-3
detail.hit.zdb_id:
218334-1
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