1. A Dynamical Model of the Beaufort Gyre: A Balance between Ekman Pumping and Eddy Fluxes Jiayan Yang & Andrey Proshutinsky Woods Hole Oceanographic Institution (jyang@whoi.edu)jyang@whoi.edu 2 nd FAMOS Workshop, Woods Hole, MA, Oct. 23-25, 2013

2. Schematic of Arctic Ocean Circulation Beaufort Gyre (http://www.whoi.edu/cms/images/oceanus)

3. wind Western Boundary Current y z Ekman Transport Ekman pumping Sverdrup Transport The 0th order dynamics of a mid-latitude gyre: BUT in the Arctic Ocean, there are some major uncertainties about the Beaufort Gyre dynamics: - does the Sverdrup balance work? - what is the removal mechanism for the low-salinity water-mass that has been accumulated by the Ekman pumping? - how the gyre is closed without a western boundary (in terms of PV, volume and momentum fluxes)

4. Beaufort Gyre Observing System (BGOS) 2003 - present

5. Summer 2003-2012 freshwater content in the BG region based on the Beaufort Gyre Observing System data. During 2003-2012, the Freshwater content in the region has increased by 5200 cubic kilometers.

6. (u 1,v 1 ) (u 2,v 2 ) A two-layer model used by Yang and Pratt (2013) for Nordic Seas Overflow

7. Forcing data: ice concentration  (NASA/GSFC), and ice velocity (NSIDC) and surface wind stress (NCEP-NCAR) The model is forced by daily surface stress

9. The model simulates the rapid increase of the FW from 2003 to 2008; The upward trend seems to stop (or slow down) after 2008; Would the upward trend start again if the forcing changes? Eddies seemed to be more abundant after 2008. What role did eddies play? And more fundamentally, what is the 0 th order dynamical balance that maintains the Beaufort Gyre?

13. North Pole Canada Basin Eddy fluxes

14. Inserting a western boundary value of  at 45N

15. Mean vorticity convergence of wind-stress curl frictional torque Advection eddy vorticity flux A1 A2 A3 A4 An Active role of eddies in the Arctic Ocean: Coarse resolutions: Eddy-resolving runs: (balance between surface and bottom Ekman layers)

16. Summary: (1)The main dynamical balance that maintains the Beaufort Gyre is between the surface wind-stress curl (Ekman pumping) and eddy PV fluxes; (2) Eddies also play a leading role in volume-transport balance, and they are likely the main removal mechanism for the accumulated fresh water in BG ; (3) Eddies are formed when the BG intensifies, the isopycnal steepens and becomes baroclinically unstable. (4) Eddy fluxes may have slowed down the upward trend in FW accumulation in BG.