DEEP WESTERN BOUNDARY CURRENT VARIABILITY AT CAPE-HATTERAS

Data from an array of inverted echo sounders and bottom current meters off Cape Hatteras, where the Gulf Stream and Deep Western Boundary Current (DWBC) cross each other, are analyzed to investigate the deep components of flow. While the mean flow is to the southwest with the DWBC, the observed temporal variability is dominated by energetic 40 day topographic Rossby waves. By optimally weighting the individual deep current meter measurements, the deep flow is averaged across the wavelength of the 40 day wave, thereby reducing the wave signal and revealing variations of the spatially averaged DWBC. The DWBC fluctuations are found to be oriented more along the isobaths than the wave motions (which have an essential cross-isobath component). Lateral path displacements of the upper layer Gulf Stream, as measured by the inverted echo sounders, are correlated with deep velocity and temperature fluctuations at specific sites, which can be understood in terms of deep Gulf Stream influence. Cross-slope flow of the spatially averaged DWBC is found to vary with changes in angle of the Gulf Stream path in a manner consistent with simple dynamics.