Internal‐tide interactions with the Gulf Stream and Middle Atlantic Bight shelfbreak front

• Published in: Journal of geophysical research. Oceans 2016-08, Vol.121 (8), p.6271-6294
• Main Authors: Kelly, Samuel M., Lermusiaux, Pierre F. J.
• Format: Article
• Language: English
• Subjects: Abyssal environment; Advection; Angle of reflection; Angles (geometry); Arrivals; Atmospheric forcing; Coastal environments; Computer simulation; Density field; Density stratification; Differential equations; Divergence; Dynamics; Energy balance; Geophysics; Gulf Stream; Interactions; internal tide; Internal tides; Marine; Mathematical models; Mesoscale features; Momentum; Monoclonal antibodies; Nonlinear dynamics; Nonlinear systems; Ocean currents; Oceans; Offshore; Partial differential equations; Primitive equations; Propagation modes; Radiation; Refraction; Rivers; shelfbreak front; Simulation; Stratification; Summer; Tidal dynamics; Tidal energy; tide; Tides; Topography; Variability; Wave reflection; Wavelengths; wave‐mean interaction
• ISSN: 2169-9275; 2169-9291
• DOI: 10.1002/2016JC011639

Internal tides in the Middle Atlantic Bight region are found to be noticeably influenced by the presence of the shelfbreak front and the Gulf Stream, using a combination of observations, equations, and data‐driven model simulations. To identify the dominant interactions of these waves with subtidal flows, vertical‐mode momentum and energy partial differential equations are derived for small‐amplitude waves in a horizontally and vertically sheared mean flow and in a horizontally and vertically variable density field. 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 shelfbreak front, which has horizontally variable stratification, 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 stratification itself, also alter internal‐tide propagation. The Gulf Stream produces anomalous regions of O(20 mW m−2) mode‐1 internal‐tide energy‐flux divergence, which are explained by tide‐mean‐flow terms in the mode‐1 energy balance. Advection explains most tide‐mean‐flow interaction, suggesting that geometric wave theory explains mode‐1 reflection and refraction at the Gulf Stream. Geometric theory predicts that offshore‐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. Key Points: Simulations of the MAB reveal internal‐tide interactions with the Gulf Stream and shelfbreak front The shelfbreak front decreases topographic generation and alters the arrival times of internal tides Tide‐mean‐flow interactions in the Gulf Stream are explained by terms in the mode‐1 momentum/energy balance