1. Some Idealized Thought Experiments of Wind-driven
Circulation in the Arctic Ocean
Jiayan Yang
Woods Hole Oceanographic Institution
Co-PI: Andrey Proshutinsky
Nov. 2, 2011, 15th AOMIP Workshop, Woods Hole, MA

3. 28-Year (1978-2006) daily Ekman transport and
upwelling on 25x25 km resolution over the whole
Arctic (Yang, 2006, J. Climate)
Data Sources:
Ice motion: NSIDC (Fowler, 2003);
Ice concentration: NASA GSFC, Greenbelt, Maryland;
Surface wind: derived from geostrophic wind from IABP

4. Today I am not going to talk about the real Arctic Ocean circulation.
I will discuss some simple but fundamental (I believe) issues that have
puzzled me in the last a few years. Something as simple as:
Question 1: how the Ekman cell is maintained?
Question 2: what is the 0th order balance in dynamics?
Question 3: can there be a quasi-steady circulation?
Question 4: where the vorticity and energy are dissipated (related to 3)?

5. The 0th order dynamics of a wind-driven gyre:
Ekman
Transport
Sverdrup
Transport
Western Boundary
Current
Ekman
pumping z
The 0th order dynamics of a wind-driven gyre:
Wind-stress curl -> Ekman pumping -> Sverdrup Transport;
Western Boundary Current closes the transport and dissipates the vorticity and energy

6. What drives this return flow?
North Pole
Canada Basin
What drives this return flow?

7. Two-layer, nonlinear model that allows
interface outcropping or grounding.
Model resolution is 5 km and uses C-grid.

8. (the reason of keeping same f0
b-plane at 85N
f-plane at 90N
b-plane: f0 set at 90N
b at 45N
(the reason of keeping same f0
is to have a same deformation radius as other exps)

9. Eddies transport mass meridionally and
North Pole
b-plane at 85N
Canada Basin
Eddies transport mass meridionally and
flux vorticity to boundary layer
Eddy fluxes
b-plane: f0 set at 90N
b at 45N
bV transport mass meridionally
(Sverdrup relation) but eddies
flux vorticity to boundary layer

10. b-plane at 85N
Inserting a western boundary

11. An Active role of eddies in the Arctic Ocean:
Mean vorticity convergence of wind-stress curl frictional torque
Advection eddy vorticity flux
A A A A4
In interior:
Along boundary:

12. The spin-up of a wind-driven circulation:
A classic view (Veronis and Stommel, 1956; Anderson and Gill, 1975):
Wind-stress curl -> barotropic and baroclinic Rossby waves
-> western boundary current
-> boundary adjustment by Kelvin waves
-> Rossby wave radiation from the eastern boundary
-> the barotropic and baroclinic modes are adjusted so that
their velocities cancel each in the abyssal layer
-> wind-driven gyre is confined in the upper layer above thermocline
The spin-up in the Arctic Ocean ?

13. Time-mean (averaged in the 11th year) flow and pressure
b-plane at 85N
Is this barotropic flow due to stagnation of
planetary Rossby waves?

14. Time-mean (averaged in the
11th year) flow and pressure
b-plane: f0 set at 90N and b at 45N.
The lower layer circulation
is still not shut down

15. Time-mean (averaged in the 11th year) flow and pressure
The classic Anderson-Gill spin-up is
recovered by inserted a western
boundary

16. Summary:
Because the Arctic Ocean has a unique geographic shape (no western
boundary) and different physical parameter (b is small), the dynamical
balance is different from that in a typical mid-latitude gyre;
(2) Eddies play a leading role in vorticity and mass fluxes;
(3) Eddies are not necessarily generated by baroclinically unstable boundary
currents. They can be originated in the interior and are required by some
fundamental dynamical balances;
(4) A non-trivial b is necessary but insufficient in achieving a Anderson-Gill
spin up that shut down the abyssal flow. A western boundary is needed.