Role of eddies in ocean circulation

1. 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?

2. Tracer distributions Circulation inferred from tracers is the ‘residual flow’ Bolus transport Residual mean Eulerian mean Rintoul Salinity WOCE SR3 Rhines Antarctica What is the role of eddy transfer in setting up? Schematic: Sverdrup

3. Infer Eddy transport from observations 1 Buoyancy transport Surface buoyancy fluxes DiabaticDeacon Cell Winds Speer,Rintoul & Sloyan 2 Eddy diffusivity, Momentum balance 3 How can we estimate a K from observations? Compare eddy stress to wind stress

4. Buoyancy Transport z 1 (i) Stream-wise average 2d (ii) Rewrite buoyancy budget: y Residual mean theory Andrews and McIntyre Held & Schneider + dia If eddies are ‘adiabatic’ Gent and McWilliams

5. Cross-stream transport inferred from air-sea fluxes from air-sea buoyancy fluxes from winds Neglecting diffusion & diabatic eddy fluxes Cross-stream transport implied by the wind is not the same as that implied by air-sea buoyancy fluxes David Marshall Speer, Rintoul & Sloyan

6. Wind Stress Air-sea buoyancy flux NCEP Out of ocean In to ocean NCEP 0 SOC DaSilva Pole Pole

7. Cross-Stream transports Sv Ekman Buoyancy fluxes ‘Inferred’ bolus transport Pole Taka Ito Can eddies achieve such a large transport? WOCE SAC climatology Gouretski and Jancke

8. Eddy mixing 2 Can we characterize eddies with a diffusivity, K? If so, how large is the K? Use ‘idealized tracer’ driven by observed surface geostrophic flow to yield K altimetry ‘idealized tracer’ Device to yield diffusivity from observations

9. Advection-diffusion in 2-d Nakamura Haynes and Shuckburgh In ‘area’ coordinates problem can be rephrased as: ‘small-scale’ diffusion Large-scale v drives small scale mixing where Theory ‘intersects’ with observations very nicely ‘dissipation rate’ of q

10. Drive tracer with altimetric data Topex dataevery 10 days Resolution Assumption: large-scale K is independent of small-scale Planning to repeat at with Emily Shuckburgh (DAMPT)Helen Jones (MIT)

11. Eddy diffusivity Near surface 2000 1500 1000 500 SCM3mooring Latitude km Phillips Implications for parameterization

12. Deducing from Sv Pole isopycnal slope at mixed layer base WOCE SAC climatology Gouretski and Jancke

13. Momentum balance 3 PV mixing Eddy PV flux PV front PV mixing 0 surface at 150m Eddy stress if Johnson and Bryden

14. Mapping down to depth Karsten, Marshall IntermediateWater (Sv) UpperCircumpolarDeep Water salinity Salinity No bottom water

15. Conclusions 1 Transport implied by and are very different must be large and oppose 30 Sv 2 Estimated from altimetry 2-d mixing of idealized tracer 500 to 2000 yields near-surface and consistent pattern of Eddies are hugely important in ACCand elsewhere….. Eddy stresses are as large as wind stress 3 4

16. Estimate of global eddy stress At 300m assuming K = 1000 Parameterized in our global climate models! using WOCE SAC climatology

17. Theory Observations Modeling Reviews