Wind-wave dissipation

Wind-wave dissipation or "swell dissipation" is process in which a wave generated via a weather system loses its mechanical energy transferred from the atmosphere via wind. Wind waves, as their name suggests, are generated by wind transferring energy from the atmosphere to the ocean's surface, capillary gravity waves play an essential role in this effect, "wind waves" or "swell" are also known as surface gravity waves.

The process of wind-wave dissipation can be explained by applying energy spectrum theory in a similar manner as for the formation of wind-waves (generally assuming spectral dissipation is a function of wave spectrum). However, although even some of recent innovative improvements for field observations (such as Banner & Babanin et al. ) have contributed to solve the riddles of wave breaking behaviors, unfortunately there hasn’t been a clear understanding for exact theories of the wind wave dissipation process still yet because of its non-linear behaviors. By past and present observations and derived theories, the physics of the ocean-wave dissipation can be categorized by its passing regions along to water depth. In deep water, wave dissipation occurs by the actions of friction or drag forces such as opposite-directed winds or viscous forces generated by turbulent flows—usually nonlinear forces. In shallow water, the behaviors of wave dissipations are mostly types of shore wave breaking (see Types of wave breaking). Some of simple general descriptions of wind-wave dissipation (defined by Luigi Cavaleri et al. ) were proposed when we consider only ocean surface waves such as wind waves. By means of the simple, the interactions of waves with the vertical structure of the upper layers of the ocean are ignored for simplified theory in many proposed mechanisms.

In general understanding, the physics of wave dissipation can be categorized by considering with its dissipation sources, such as 1) wave breaking 2) wave–turbulence interaction 3) wave–wave modulation respectively. (descriptions below of this chapter also follow the reference )

1) dissipation by "wave breaking"

Wind-wave breaking at coastal area is a major source of the wind-wave dissipation. The wind waves lose their energy to the shore or sometimes back to the ocean when those break at the shore. (see more explains -> “Ocean surface wave breaking”)

2) dissipation by "wave–turbulence interaction"

The turbulent wind flows and viscous eddies inside waves can both affect wave dissipation. In the very early understandings, the viscosity can barely affect on the wind waves so that the dissipation of the swells by viscosity also barely considered. However, recent weather forecasting models begin considering “wave-turbulence interaction” for the wave modeling. It is still arguable how much the turbulent-induced dissipations contribute to change the whole wave profiles, but the ideas of wave-turbulence interaction for surface viscous layers and wave bottom boundary layers are recently accepted.

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