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Role of eddies in ocean circulation. Ocean is full of geostrophic turbulence. Models suggest eddies play major role in tracer, momentum and vorticity budgets. e.g. vanishing of ‘Deacon Cell’. TOPEX. Doos and Webb. Danabasoglu, McWilliams. But. What can we infer from observations?. - PowerPoint PPT Presentation
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Role of eddies in ocean circulation
TOPEXe.g. vanishing of ‘Deacon Cell’
What can we infer from observations?What can we infer from observations?
Doos and Webb
Danabasoglu, McWilliams
• Models suggest eddies play major role in tracer, momentum and vorticity budgets
But
• Ocean is full of geostrophic turbulence
h212
WOCE SR3
Schematic: Sverdrup
Tracer distributions
Salinity
vR v v
Residual mean
Eulerian mean
Bolus transport
Rhines
Rintoul
Circulation inferred from tracers is the ‘residual flow’
Circulation inferred from tracers is the ‘residual flow’
vh
hAntarctica
vhh
What is the role of eddy transfer in setting up ?
What is the role of eddy transfer in setting up ? vR
vR
Infer Eddy transport from observations
Winds
Surface buoyancy fluxes
v
vR
1
v
2 3 Momentum balance
Buoyancy transport
Eddy diffusivity,
Compare eddy stress to wind stress
KHow can we estimate a K from observations?
vR v vv
vDiabatic
Deacon Cell
Speer,Rintoul & Sloyan
Buoyancy Transport
Rewrite buoyancy budget:
Stream-wise average
2d (i)
(ii)
y
vb
z v v by w w b
z B z
vb
b z
+ dia
Andrews and McIntyre
Held & Schneider
1
wb
b y
Residual mean theoryResidual mean theory
Gent and McWilliamsIf eddies are ‘adiabatic’
Cross-stream transport inferred from air-sea fluxes
from winds
Speer, Rintoul & Sloyan
R by Bs from air-sea
buoyancy fluxes
Neglecting diffusion & diabatic eddy fluxesNeglecting diffusion & diabatic eddy fluxes
f
David Marshall
Cross-stream transport implied by the wind is not the same as that implied by air-sea buoyancy fluxes
Cross-stream transport implied by the wind is not the same as that implied by air-sea buoyancy fluxes
Air-sea buoyancy fluxWind Stress
NCEP
SOC DaSilva
53.553.5
0.1
0.14
0 Pole Pole 60oS60oS 4646
0
NCEP
Bs x Nm 2
In to ocean
Out of ocean
Cross-Stream transports
Buoyancy fluxes
Can eddies achieve such a large transport?Can eddies achieve such a large transport?
R Bs by
R
58 54 5062S 46
20
40
20
40
0
Sv
Ekman
‘Inferred’ bolus transport
Taka ItoPole
WOCE SAC climatology
Gouretski and Jancke
Eddy mixing
If so, how large is the K?
2
Use ‘idealized tracer’ driven by observed surface geostrophic flow to yield KUse ‘idealized tracer’ driven by observed surface geostrophic flow to yield K
Can we characterize eddies with a diffusivity, K?
Device to yield diffusivity from observations
‘idealized tracer’
altimetry
Large-scale v drives small scale mixing
Advection-diffusion in 2-dNakamura
‘small-scale’ diffusion
q t v q k 2q
In ‘area’ coordinates problem can be rephrased as:
k A
Aq,t
|q|2dA
q t
A K qA
where K qA
2
Haynes and Shuckburgh
kqkq
‘dissipation rate’ of qTheory ‘intersects’ with observations very nicely
Theory ‘intersects’ with observations very nicely
Drive tracer with altimetric data
Assumption: large-scale K is independent of small-scale
q t v q k 2q
Topex dataevery 10 days
Emily Shuckburgh (DAMPT)Helen Jones (MIT)
k 100m2s 1
16
16
Planning to repeat at130
130
Resolution
k 10m2s 1with
k
Eddy diffusivity
K m2s 1
2000
1000
50 40 3060 S
500
Latitude
Near surface
Phillipskm
m2s 1
SCM3mooring
K
1500
Implications for parameterizationImplications for parameterization
K
R Bs by
Deducing from
isopycnal slope at mixed layer base
WOCE SAC climatology
20
40
20
40
0
Sv
58 54 5062S 46
K
s b y
b z
R
Gouretski and Jancke
Pole vb
b z
Ks
fvR F vqPV mixing
PV mixing
PV front
vvv
Momentum balance
wind
eddy
surface0
Johnson and Bryden eddy wind R 0if
at 150m
Nm 2
v
0.1 0.20 0.1 0.2
3
Eddy stress
Eddy f fKs
wind z
Eddy z
Eddy PV flux
Mapping down to depth
salinity
No bottom water
Karsten, Marshall
UpperCircumpolarDeep Water
(Sv) R
IntermediateWater
Salinity
vv
Conclusions1
2
2-d mixing of idealized tracer
3
must be large and oppose
Estimated from altimetry
yields near-surface
Eddy stresses are as large as wind stress
4 Eddies are hugely important in ACCand elsewhere…..
500 to 2000K m2s 1
K
Transport implied by and are very different
30 Sv
and consistent pattern of
Bs
Estimate of global eddy stress
assuming K = 1000
Nm 2
using WOCE SAC climatology
At 300m
m2s 1 Parameterized in our global climate models!
Parameterized in our global climate models!
0.1 0.2 0.1 0.2 0
ObservationsTheory
Modeling
ReviewsNowlin and Klink, 1986Rintoul, Hughes and Olbers, 2001
Bryden,1979Gille,1997Phillips and Rintoul, 2000Speer, Rintoul and Sloyan, 2000Karsten and Marshall, 2002Gille, 2002
Munk and Palmén, 1951deSzoeke and Levine, 1981Marshall, 1982Johnson and Bryden, 1989Gent and McWilliams, 1990Marshall, Olbers, et al, 1993Nakamura, 1996David Marshall, 1997McDougall,1998Haynes and Shuckburgh, 2001Olbers and Ivchenko, 2002Marshall and Radko, 2002
McWilliams, Holland and Chow, 1978Semtner, Chervin, 1992Döös and Webb 1994Danabasoglu, McWilliams 1994Ivchenko, Richards, Stevens 1996