A Dynamical Model of the Beaufort Gyre A
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) 2 nd FAMOS Workshop, Woods Hole, MA, Oct. 23 -25, 2013
Schematic of Arctic Ocean Circulation Beaufort Gyre (http: //www. whoi. edu/cms/images/oceanus)
y Ekman Transport Ekman pumping S Tr verd an ru sp p or t W C es ur te re rn nt B ou nd ar y wind z BUT in the Arctic Ocean, there are some major uncertainties about the Beaufort Gyre dynamics: The 0 th order dynamics of a mid-latitude gyre: - 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)
Beaufort Gyre Observing System (BGOS) 2003 - present
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.
(u 1, v 1) (u 2, v 2) A two-layer model used by Yang and Pratt (2013) for Nordic Seas Overflow
The model is forced by daily surface stress Forcing data: ice concentration s (NASA/GSFC), and ice velocity (NSIDC) and surface wind stress (NCEP-NCAR)
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?
North Pole Canada Basin Eddy fluxes
value of b at 45 N Inserting a western boundary
An Active role of eddies in the Arctic Ocean: Mean vorticity Advection convergence of eddy vorticity flux wind-stress curl frictional torque A 2 A 3 A 4 A 1 Eddy-resolving runs: Coarse resolutions: (balance between surface and bottom Ekman layers)
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.
- Slides: 16
