Ocean surface wave

Physical characteristics

Key parameters include wavelength (distance between successive crests), period (time between crests passing a fixed point), amplitude (half the vertical difference between crest and trough), frequency and propagation speed. In deep water, waves of different wavelengths separate by dispersion: longer waves travel faster. In shallow water, wave speed depends mainly on depth. When depth decreases relative to wavelength, waves slow, shorten, and increase in height.

Generation and propagation

Wind transfers momentum to the sea through pressure fluctuations and surface shear across a fetch. Storm systems create complex seas that can evolve into swell — organized groups of waves that radiate away and travel thousands of kilometers. Geologic sources produce very long-wavelength waves (tsunamis) that can cross ocean basins with comparatively little loss of energy until they approach shallow coasts.

Measurement and observation

Waves are observed by in situ instruments such as buoys and pressure sensors, by coastal tide gauges, and by remote sensing from radar and satellites. Time series of sea surface elevation and spectral analysis reveal dominant periods and energy distribution. Operational services and monitoring networks provide forecasts and warnings based on wind fields and seismic data.

Coastal interaction and breaking

As waves approach shore they undergo shoaling, refraction, diffraction and sometimes reflection. Shoaling increases wave height because the lower part of the orbit is slowed by the seabed while the upper part continues, producing instability and eventual breaking. Breaking dissipates energy, redistributes sediment, shapes beaches and can cause coastal erosion or accretion depending on local conditions.

Types, hazards and uses

• Wind waves: locally generated, typically shorter period and choppier.
• Swell: longer-period, better organized waves that travel away from storms.
• Tsunamis: long-wavelength waves from geologic events that can cause severe coastal damage.
• Rogue waves: occasionally occurring, unusually large single waves from complex interactions.

Understanding surface waves is important for navigation, coastal engineering, hazard mitigation, recreational activities such as surfing, and for technologies that capture wave energy. For general introductions and technical references consult introductory portals and monitoring programs at regional centres: see weather and wind analyses at meteorological sources, seismic and tsunami information via seismic networks, long-travel behavior in ocean portals at related portals, and basic educational material on surface wave basics and the upper ocean. Practical guidance on wave energy and coastal design is available from specialist literature and engineering standards (wave energy) and operational forecasts and advisories (momentum and transport).