| Summary: | Density variations along the western and eastern boundaries of an ocean basin play an important role in constraining the meridional overturning circulation (MOC). Climatological maps of hydrographic properties along the sloping western and eastern boundaries of the Atlantic reveal a clear asymmetry. Along the western boundary a systematic north-south gradient in neutral density is found, associated with the large-scale MOC; in contrast, along the eastern boundary, netural density surfaces are virtually flat, consistent with classical ideas about the inability of eastern boundaries to support large-scale horizontal pressure gradients. This asymmetry breaks down in the bottom layers where Antarctic Bottom Water spreads northwards as topographic slope currents. Similar pictures are found in the Pacific and Indian basins, except that the western boundary variations in neutral density are much reduced due to the absence of significant meridioinal overturning. Moreover, recent theoretical and modelling results will be discussed which suggest that this asymmetry carries over interannual variability in density variations along the western and eastern boundaries and hence the MOC. The above serves as the motivation for the WAVE (Western Atlantic Variability Experiment) array deployed in 2004 at three locations along the western margin of the deep North Atlantic, as part of prototype MOC monitoing array developed under the UK RAPID program. The array consists of three lines of bottom pressure recorders, inverted echo sounders and moorings. The aims are to identify how changes in the circulation of the deep western boundary current are communicated from their high latitude sources along the western margin of the North Atlantic, and to test a fundamental assumption of any practical monitoring system for the North Atlantic MOC - that a substantial component of the changes in circulation is coherent across latitude circles. The relation of the RAPID arrays to the wider international MOC monitoring system emerging under the ...
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