Title: An Eddy-resolving State Estimate of the Ocean Circulation during the Subduction
Experiment using a North Atlantic Regional Model (ECCO).

Authors:
Geoffrey Gebbie, MIT-WHOI
Carl Wunsch, MIT
Patrick Heimbach, MIT 

An eddy-resolving ocean state estimate during the Subduction Experiment is made
by bringing a 1/6 degree North Atlantic regional model into consistency with
data through the adjoint method. A novel aspect of this work is the search for
an initial eddy field and eddy-scale open boundary conditions by the use of an
adjoint model. The adjoint model for this region of the ocean is stable and
yields useful information despite concerns about the chaotic nature of an
eddy-resolving model. Observations employed in this study are TOPEX/POSEIDON
satellite altimetry and mooring data from the Subduction Experiment. When
rigorous, statistical consistency is found between this dataset and the model,
we not only have a best estimate for the ocean state, but we have also acquired
a best estimate for the initial eddy field, open boundary conditions, wind
stresses, and air-sea fluxes. This study quantifies the ability of the data to
constrain both the large scale circulation and the eddy scale. Individual eddy
trajectories can also be determined. The final state estimate is dynamically
consistent with the General Circulation Model. Thus, we can readily diagnose
subduction rates, heat and other budgets from the result in a physically
interpretable context. In particular, the state estimate permits improved
understanding of the impact of eddies on the large scale process of
subduction. This work is part of the ECCO Consortium effort directed at greatly
improved estimates of the oceanic general circulation through state estimation
methods.