Wind-Generated Water Waves: Two Overlooked Mechanisms?

Abstract

Prom research on stratospheric dynamics there has emerged what might prove to be some useful fresh ideas about the problem of water-wave generation by wind. As pointed out in an earlier contribution (1993), water waves can be systematically amplified by two irreversible, ratchet-like mechanisms that depend on spatio-temporal inhomogeneities, such as wind gustiness and wave groupiness. Neither mechanism is represented in the models used for wind-wave forecasting. The first mechanism is simply the drag from what might be called Rossby or vorticity lee waves in the airflow downstream of water-wave groups. The second is intermittent Rossby-wave breaking or vertical mixing of spanwise horizontal vorticity in the airflow, a highly nonlinear, non-Fourier-superposable mechanism. Both mechanisms can amplify nonbreaking water waves, as well as contributing to the amplification of breaking water waves.