Wave Dynamics And Wind Waves

What is a wave? A disturbance caused by movement of energy from a source (wind, earthquake, etc.) through a medium(water). Note: Wave energy passes through water….. Water does not move along with the wave

Consider the following…….

Orbital waves: Water particles move in closed Ocean waves are: Orbital waves: Water particles move in closed circles as wave energy passes. And also… Progressive waves : move forward in one direction.

Progressive Waves Deep –water wave: Wave traveling through water deeper than ½ wavelength.

Progressive Waves Transitional wave: depth less than ½ wavelength and deeper than 1/20 wavelength. (Orbits become elliptical, wave drags bottom.) Shallow-water wave: wave traveling through water w/ depth less than 1/20 wavelength.

Stokes Drift: Small net transport of water in the direction of wave movement. Particle speed decreases with depth……therefore molecules at top of orbit move further forward than molecules at bottom of orbit move backward.

Classifying Waves: Disturbing force: energy that causes waves. Waves are classified by disturbing force, the extent to which the disturbing force continues to influence the waves after they form, restoring force, and wavelength. Disturbing force: energy that causes waves. Restoring force: dominant force trying to restore the surface to flat.

Types of Waves: Wind waves Typical wavelength: 60-150m(200-500ft.) Disturbing force: wind Restoring force: gravity

Types of Waves: Seiche. Typical wavelength: large, variable, a function of basin size. Disturbing force: change in air pressure, storm surge, tsunami.

Types of Waves Tsunami Typical wavelength: 200km. (125mi.) Disturbing force: earthquake on sea floor, volcanic eruption, landslide Restoring force: gravity

Consider the following……..

Wind Waves Begin as capillary waves and build into larger wind waves. Wave size depends on wind strength, duration, and fetch. Capillary wave: tiny ripples (wl less than 1.73 cm.) that are the 1st to form when wind starts to blow.

Duration: How long the wind blows. Strength: Wind speed Duration: How long the wind blows. Fetch: Distance over which the wind blows. Fully developed sea: waves are max. size for specific strength, duration ,and fetch.

Swell Formation and Dispersion Because waves w/ longest wavelengths move fastest, they leave the area of wave formation sooner than waves w/ shorter wavelengths. Therefore, mature waves from a storm sort themselves into groups of similar wavelengths and speeds. This sorting is called dispersion and it creates swell . Progressing groups of swell are called wave trains.

Wave Interference Waves from different wave trains meet and combine in the ocean. Constructive interference: waves add to each other. Destructive interference: waves subtract from each other.

Consider the following……….

Rogue waves: Huge wave caused by constructive interference of two or more waves coming together in the same place at the same time.

Waves Approaching the Shoreline When ocean waves approach the shoreline, they begin to “drag” the bottom at a depth = ½ wavelength. This “drag” slows the waves down, allowing following waves to catch up. Wavelengths get shorter, heights get taller. When wave height reaches 7x wavelength, the wave becomes unstable and breaks.

Types of Breakers Plunging breakers: Occur with medium sloped bottom. Waves curl to form tube (preferred by surfers)

Types of Breakers Spilling Breakers: Occur with flat or gently sloped bottom.

Wave Refraction Slowing and bending of waves in shallow water. Waves bend to shape of coastline.

Diffraction Waves bend around an obstacle. (islands, rocks, pilings, etc.)

Wave Reflection When waves strike an obstruction head-on, they “bounce” back in the opposite direction.

Pretty cool, huh? THE END!!!!!!