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Focusing of internal tides by near‐inertial waves
Author(s) -
Cuypers Y.,
BouruetAubertot P.,
Vialard J.,
McPhaden M. J.
Publication year - 2017
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1002/2017gl072625
Subject(s) - internal wave , baroclinity , inertial wave , geology , internal tide , geophysics , inertial frame of reference , refraction , ray tracing (physics) , geodesy , wave propagation , physics , oceanography , mechanical wave , optics , longitudinal wave , classical mechanics
The refraction of internal waves by lower‐frequency near‐inertial waves has been predicted theoretically, but never observed before. Here, we report observations of semi‐diurnal internal tides generated by the rough topography of the Central Indian Ridge, in the presence of a strong, lower‐frequency near‐inertial wave field generated by a tropical storm. The semi‐diurnal internal tide energy is trapped within upward propagating bands with a periodicity close to the inertial period. A ray‐tracing model suggests that this trapping results from the internal tide refraction by the shear associated with near‐inertial waves. This yields a strong increase of the internal tide energy and shear in space‐time regions where the background flow focuses the rays, leading to the formation of caustics. This mechanism may increase vertical mixing generated by baroclinic tides in the vicinity of mid‐ocean ridges in tropical regions.