AN INVERSE MODEL OF THE NORTH-ATLANTIC GENERAL-CIRCULATION USING LAGRANGIAN FLOAT DATA

A nonlinear finite-difference inverse model is used for estimating the North Atlantic general circulation between 20-degrees and 50-degrees- N. The inverse model with grid spacing 2-degrees latitude and 2.5-degr ees longitude is based on hydrography and is in geostrophic and hydros tatic balances. The constraints of the inverse model are surface and s ubsurface float mean velocities; Ekman pumping derived from wind data; conservations of mass, heat, and salt; and the planetary vorticity eq uation at the reference level. The mass, heat, and salt conservations are applied in a vertically integrated form. The model does not have e xplicit mixing or air-sea flux terms. Vertical velocities result from the nondivergence of the 3D velocity field. After inversion, float vel ocities, hydrographic data, and dynamical constraints are generally co mpatible within error bounds. A few float velocities are, however, rej ected by the model mainly due to inadequate time or space sampling of the 2-degrees latitude by 5-degrees longitude boxes for which mean flo at velocities are computed. The resulting circulation shows a maximum Gulf Stream transport close to 130 X 10(6) m3 s-1 at 64-degrees-W. Res iduals of the vertically integrated heat and salt conservation constra ints may be interpreted as air-sea fluxes and are of the right order o f magnitude as compared to in situ measurements. The float database us ed is already important particularly at the surface. However, its addi tion to the inversion does not change substantially the estimation by the model of integrated quantities, such as Gulf Stream transports, as compared to an inversion using hydrography and dynamical constraints alone. But floats significantly affect the estimation of the deep circ ulation increasing, for instance, the estimated velocity amplitude for the deep western boundary current flowing westward south of the Grand Banks.