Low-frequency variability on the western flanks of the Grand Banks

Abstract

An array consisting of 21 current meters on nine moorings was set on the western flanks of the Grand Banks in August 1995 and recovered about two years later. The purpose was to explore the possibility that this might be a region of anomalously high topographic wave activity because the local topography so altered the dispersion relation for these waves that they could couple more readily to eastward-moving Gulf Stream meanders. Eddy kinetic energy is, indeed, found to be higher here than elsewhere in the region but only at periods shorter than about 10 days. At longer periods energy in near-bottom motions is mainly a function of cross-slope position (or water depth) and, surprisingly, is more or less independent of alongslope position. The mechanism for enhancement of the higher frequency variability is unclear but it does not appear to be related to the hypothesized coupling with eastward-traveling meanders. Instead, it is more likely to be associated with forcing by transient motions of the Gulf Stream, which is able to excite a broadband response. The mean circulation and climatology of the low-frequency eddy field in the region of the array are also discussed.