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On the Unsteady Steepening of Short Gravity Waves Near the Crests of Longer Waves in the Absence of Generation or Dissipation
Author(s) -
Peureux Charles,
Ardhuin Fabrice,
Guimarães Pedro Veras
Publication year - 2021
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
eISSN - 2169-9291
pISSN - 2169-9275
DOI - 10.1029/2020jc016735
Subject(s) - breaking wave , physics , instability , dissipation , wind wave , gravity wave , mechanical wave , mechanics , action (physics) , gravitational wave , surface wave , phase (matter) , infragravity wave , longitudinal wave , range (aeronautics) , classical mechanics , wave propagation , optics , astrophysics , quantum mechanics , materials science , composite material , thermodynamics
The wave action equation provides a general framework that has been applied to the conservative hydrodynamic interactions between short and long surface waves. So far, only a limited range of solutions have been investigated. Here, we show that the wave action equation predicts that groups of short waves propagating over long monochromatic waves are unstable. We demonstrate theoretically and numerically, a new ratchet‐type instability that progressively condenses short wave action around the long wave crests due to the correlation of phase speed and action fluctuations. This instability is of particular interest because it may lead to a higher probability of breaking for short waves propagating in directions within ±35 degrees of the dominant waves direction. This preferred breaking could has a strong impact on cross‐ and down‐wind slope statistics and thus air‐sea exchanges and remote sensing.