DYNAMICALLY CONSISTENT HYDROGRAPHY AND ABSOLUTE VELOCITY IN THE EASTERN NORTH-ATLANTIC OCEAN

The problem of mapping a dynamically consistent hydrographic field and associated absolute geostrophic flow in the eastern North Atlantic be tween 24-degrees and 36-degrees-N is related directly to the solution of the so-called thermocline equations. A nonlinear optimization probl em involving Needler's P equation is solved to find the hydrography an d resulting flow that minimizes the vertical mixing above about 1500 m in the ocean and is simultaneously consistent with the observations. A sharp minimum (at least in some dimensions) is found, apparently cor responding to a solution nearly conserving potential vorticity and wit h vertical eddy coefficient less than about 10(-5) m2/s. Estimates of ''residual'' quantities such as eddy coefficients are extremely sensit ive to slight modifications to the observed fields. Boundary condition s, vertical velocities, etc., are a product of the optimization and pr oduce estimates differing quantitatively from prior ones relying direc tly upon observed hydrography. The results are generally insensitive t o particular elements of the solution methodology, but many questions remain concerning the extent to which different synoptic sections can be asserted to represent the same ocean. The method can be regarded as a practical generalization of the beta spiral and geostrophic balance inverses for the estimate of absolute geostrophic flows. Numerous imp rovements to the methodology used in this preliminary attempt are poss ible.