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During 1979–1980, an array of inverted echo sounders (IES) and three deep current meter moorings were deployed on the continental slope 100–200 km northeast of Cape Hatteras, North Carolina. This array continuously monitored the path of the Gulf Stream and the deep currents under it. The mean currents at two sites 1000 m off the bottom near the northern edge of the stream were veered to the right of the mean surface path, indicating a deep inflow to the stream. Mean currents 500 and 1000 m off the bottom 50 km farther offshore were northeastward, nearly colinear with the surface Gulf Stream path. The deep velocity fluctuations are characterized by a transition from transverse flow aligned with the local bathymetry for periods longer than about 12 days to fluctuations with a cross-stream orientation for shorter periods. For periods between 4 days and 1 month, cross-stream movements of the Gulf Stream temperature front are vertically coherent and nearly barotropic, based on correlations between the IES-measured stream path and deep temperature fluctuations. Temperature fluctuations at the current meter sites lead cross-stream (positive onshore) velocity fluctuations by approximately 90°. Consideration of the nondiffusive fluctuating heat equation for deep layers suggests a three-term balance between local rate of change, cross-stream horizontal advection, and vertical advection of temperature, with the first two being of like sign. Kinematically, this requires |wTz| > |υTy|, so that parcel trajectories in the cross-stream plane are inclined at angles steeper than the mean cross-stream slope of the isotherms. Eddy energy conversion between the fluctuations and the mean field in deep layers is predominantly baroclinic, with e-folding growth time scales of approximately 10 days.

Publication Title, e.g., Journal

Journal of Geophysical Research