Detailed structure of currents and hydrography on the northern side of Georges Bank

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Abstract
A suite of observations from July 2–3, 1988, is used to describe the spatial structure and temporal evolution over the tidal period of currents and hydrography across the northern side of Georges Bank in summer under light winds. The data set includes moored current and hydrographic observations at four cross‐bank positions, fast response thermistor chain observations at two of the sites, a conductivity‐temperature‐depth section, 10 repeated sections over the tidal period using a towed Batfish and ship‐mounted acoustic Doppler current profiler, and two surface drifter trajectories. The observations provide a detailed description of previously identified features such as the strong semidiurnal tidal currents, an internal tide, a tidal front, and a residual current jet and also reveal a hierarchy of energetic smaller‐scale structures. These include an internal hydraulic jump during off‐bank tidal flow and subsequent internal waves propagating onto the bank and also a surface convergence in the frontal zone. The physical oceanographic regime on the northern side of Georges Bank during spring‐fall can be conceptualized as a hybrid of a stratified shelf break with strong tidal advection and a tidal(mixing) front. Key factors to the regime are the strong tidal currents and abrupt topographic variation over the bank's side. The result is a nonlinear and baroclinic tide‐topography interaction at the bank edge and a frontal zone with strong variability over the tidal period associated with tidal advection and large‐amplitude internal waves. The along‐bank transport in the residual jet is estimated to be 0.91 Sv, indicating that it may be the largest summertime transport feature on the northwestern Atlantic shelf between Cape Hatteras and the Grand Bank.