OCNG 251 Brooks Spring 13 Topical Study Guide for Exam 3 Ch 8 Waves Wave nomenclature wavelength period height steepness frequency speed Crests high parts of waves Troughs low parts of waves Still water level zero energy level level of water if there were no waves Wave height H the vertical distance between a crest and a trough Wavelength L horizontal distance between any two corresponding points on successive waveforms Wave steepness the ration of wave height to wavelength Wave period T the time it takes on full wavelength to pass a fixed position Frequency f the number of wave crests passing a fixed location per unit of time and is the inverse of the period Wave Base L 2 one half the wavelength Wave types capillary gravity wind tsunami internal standing Disturbing Forces all waves begin as disturbing forces the energy causes ocean waves to form Waves are formed by wind across the surface and by the movement of fluids with different densities o Wind generates most ocean wave o Interface Air water ocean waves movement of air across the ocean surface Air air atmospheric waves movement of different air masses Water water internal waves movement of water of different densities Mass movement also creates waves splash waves o The uplift or down dropping of large areas on the sea floor can release large amounts of energy moving the entire column of water above it Tides are also a type of wave caused mainly by the gravitational pull of the Moon and the Sun A wake is also a wave Wave types o Longitudinal like sound waves push pull waves the particles vibrate in the same direction that the energy is traveling The shape of the wave moves through the medium by compressing and decompressing as it goes o Transverse Waves energy travels at a right angle to the direction of the vibrating particles like a the waveform moves up and down but the motion is at right angles to the direction in which energy is transmitted transmit energy only through solids because the particles in solids are bound to one another strongly enough to transmit this kind of motion o Orbital Waves the movement of particles in ocean waves involves components of both longitudinal waves and transverse waves Circular Orbital Motion as the wave travels the water passes the energy along by moving in a circle o This motion allows a waveform to move forward through the water while the individual water particles that transmit the wave move around in a circle and return to essentially the same place o The circular orbits of an object floating at the surface have a diameter equal to the wave height o Circular motion quickly dies below the surface o At some depth they become small their motion is negligible This depth is called the wave base L o Tsunami generated by earthquakes in the ocean floor Very long wavelength waves meaning they are always shallow water waves o Tides a type of wave generated by the gravitational attraction of the Moon and the Sun o Capillary Waves deformations in the ocean surface in the shape of rounded waves with V shaped troughs d wavelengths less than 1 74 cm results from surface tension in water o Gravity Waves symmetric waves that have wavelengths exceeding 1 74 cm rope Form as more energy is transferred to the ocean Length is generally 15 to 35 times their height Wave height increases more rapidly than wavelength The crests become pointed and the troughs are rounded resulting in a trichoidal waveform Characteristics of waves in deep water and shallow water speed particle motions Deep Water Waves If the water depth is greater than the wave base the waves are deep water waves o Have no interference with the ocean bottom Wave speed is the rate at which a wave travels o Distance divided by time o Known as celerity The speed of deep water waves is dependent upon Used only in relation to waves where no mass is in motion just the waveform Several other variables that remain constant on Earth o Wavelength o o The equation for deep water wave speed varies only with wavelength o In summary the general relationship for deep water waves is the longer the wavelength the faster the wave travels o A fast wave does not necessarily have a large wave height because wave speed depends only on wavelength Shallow Water Waves Waves in which depth is less that 1 20 of the wavelength are called shallow water waves or long waves o Shallow water waves are said to touch bottom because they touch the ocean floor which interferes with the wave s orbital motion o The speed of shallow water waves in influenced only by gravitational acceleration and water depth Mainly water depth The deeper the water the faster the wave o Particle motion in shallow water waves is in a very flat elliptical orbit that approaches horizontal oscillation o The vertical component of particle motion decreases with increasing depth causing the orbits to become even more flat Transitional Waves have characteristics of both deep and shallow water waves o Wavelengths are between 2 and 20 times the depth of the water o The speed of transitional waves depends partially on water depth and partially on wavelength o o o o Waves break in the surf zone because particle motion at the bottom of the wave is restricted meaning the top of the wave literally runs over itself Spilling Breaker a turbulent mass of air and water that runs down the front slope of the wave as it breaks Results from a gently sloped ocean floor Plunging Breaker has a curling crest that moves over an air pocket The curling crest occurs because the particles in the crest outrun the wave and there is nothing beneath them to support their motion Form on moderately steep beach slopes best surf Surging breaker when the ocean has an abrupt slope the wave energy is compressed into shorter distances and the wave surges forward Sea the area where wind driven waves are generated Swell uniform symmetrical waves that have traveled out of their area of origination o As waves generated in a sea area move toward its margins wind speeds diminish and the waves eventually move faster than the winds o Wave steepness decreases and waves become long crested waves called swells o Little loss of energy over large stretches of ocean surface occur in swells o Transporting of energy from one area and depositing it in another Wind generated waves sea swell surf and breakers p240 Breakers whitecaps when steepness reaches a critical value of 1 7 o Wave trains group of waves o Wave dispersion the progression from long fast waves