Low-frequency currents at the northern shelf edge

The structure and generation mechanisms of low-frequency currents at the northern shelf edge region of the Grand Banks are investigated using data from a bottom mounted acoustic Doppler current profiler (ADCP) and an array of conventional current meters collected during the Canadian Atlantic Storms Program II. The vertical structure of the current is determined from an empirical orthogonal function analysis of the ADCP data. The analysis shows that over the shelf edge the low-frequency currents are predominantly barotropic and polarized in the long-shelf direction. There is little coherence between the local wind and the barotropic current, while baroclinic currents are moderately coherent with the local wind. In the interior of the shelf, the currents and the local wind are highly coherent. The difference in response to wind forcing over the shelf edge and in the shelf interior suggests that currents in the shelf interior are wind driven, while currents over the shelf edge are generated by mechanisms other than direct wind forcing. Possible generation mechanisms for the barotropic long-shelf low-frequency currents are discussed, including meanders and eddy formation in the Labrador Current and continental shelf waves generated by distant storms.

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