Monitoring the meridional overturning circulation in the North Atlantic: a model-based array design study

Baehr, J., Hirschi, J., Beismann, J.O. and Marotzke, J. (2004) Monitoring the meridional overturning circulation in the North Atlantic: a model-based array design study. Journal of Marine Research, 62 (3), 283-312. (doi:10.1357/0022240041446191).

Abstract

A monitoring system for the meridional overturning circulation (MOC) is deployed into an "eddy-permitting" numerical model (FLAME) at three different latitudes in the North Atlantic Ocean. The MOC is estimated by adding contributions related to Ekman transports to those associated with the zonally integrated vertical velocity shear. Ekman transports are inferred from surface wind stress, whereas the velocity shear is derived from continuous density "observations," principally near the eastern and western boundaries, employing thermal wind balance. The objective is to test the method and array setups for possible real observation in the ocean at the chosen latitudes and to guide similar tests at different latitudes. Different "mooring placements" are tested, ranging from a minimal setup to the theoretical maximum number of "measurements." A relatively small number of vertical density profiles (about 10, the exact number depending on the latitude) can achieve a reconstruction of the MOC similar to one achieved by any larger number of profiles. However, the main characteristics of the MOC can only be reproduced at latitudes where bottom velocities are small, here at 26N and 36N. For high bottom velocities, in FLAME at 53N, the array fails to reproduce the strength and variability of the MOC because the depth-averaged flow cannot be reconstructed accurately. In FLAME, knowledge of the complete bottom velocity field could substitute for the knowledge of the depth-averaged velocity field.

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