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Internal-tide Interactions with the Gulf Stream and Middle Atlantic Bight Shelfbreak Front

Kelly, S.M. and P.F.J. Lermusiaux, 2016. Internal-tide Interactions with Gulf Stream and Middle Atlantic Blight Shelfbreak Front. Journal of Geophysical Research - Oceans, 121, 6271–6294, doi:10.1002/2016JC011639.

Internal tides in the Middle Atlantic Bight region are noticeably influenced by the presence of the shelfbreak front and the Gulf Stream. To identify the dominant interactions of these waves with subtidal flows, vertical-mode momentum and energy partial di fferential equations are derived for small-amplitude waves in a horizontally and vertically sheared mean flow and in a horizontally and vertically variable density fi eld. First, the energy balances are examined in idealized simulations with mode-1 internal tides propagating across and along the Gulf Stream. Next, the fully-nonlinear dynamics of regional tide-mean flow interactions are simulated with a primitive equation model, which incorporates realistic summer mesoscale features and atmospheric forcing. The summer shelfbreak front, which has horizontally variable strati cation, decreases topographic internal-tide generation by about 10% and alters the wavelengths and arrival times of locally generated mode-1 internal tides on the shelf and in the abyss. The (sub)-mesoscale variability at the front and on the shelf, as well as the summer strati cation itself, also alter the internal tide propagation. The Gulf Stream produces anomalous regions of O(20 mW m2) mode-1 internal-tide energy-flux divergence, which are explained by mean-flow terms in the mode-1 energy balance. Advection explains most tide-mean flow interaction, suggesting that geometric wave theory predicts mode-1 reflection and refraction at the Gulf Stream. Geometric theory predicts that o ffshore-propagating mode-1 internal tides that strike the Gulf Stream at oblique angles (more than thirty degrees from normal) are reflected back to the coastal ocean, preventing their radiation into the central North Atlantic.