Vorticity Balance in the ECCO Global WOCE Synthesis 

Y. Lu and D. Stammer for the ECCO Consortium.

From an ocean model that was constrained by WOCE data sets as 
part of the NOPP-funded ECCO assimilation project,  we analyze 
the barotropic vorticity budget of the global ocean. 

For the depth-integrated circulation, it is found that the
bottom pressure torque (BPT) dominates over the curl of friction
in the western boundary currents and in the Southern Ocean.
This important role played by BPT in the dynamics of the western
boundary currents and the Antarctic Circumpolar Current (ACC),
as found in this 2 degree-resolution simulation, is consistent
with the recent theoretical argument and the analyses of
eddy-resolving simulations.

In the upper layer of the model, the classical Sverdrup balance
holds only in the eastern sub-tropical basins. The vorticity
stretching/compressing associated with the vertical velocity
is important near western boundary currents and in at high latitudes.
In the intermediate layer, the vorticity stretching/compressing
associated with vertical motions drive the meridional flow
in the interior basins.

For the deep ocean, it is the combination of BPT and the vertical
velocity that balances the advection of planetary vorticity.
The meridional flow in the abyssal ocean is driven
by the combined effect of BPT and vertical motions.
The simulated abyssal circulation in the interior basins bears
little resemblance with the prediction of the Stommel-Arons theory.