Ocean Waves

factors determining the amount of energy in a wave

(1) wind speed (2) duration (3) fetch-the distance over which the wind blows in one direction "60 foot rue" is theoretical maximum height of a wave, accepted as fact But there are accounts of higher waves like the 112 foot wave on the Ramapo

wave reflection

a vertical barrier can reflect waves back into the ocean with little loss of energy -often interferes with next incoming waves and creates unusually waveforms

sea

area where wind-drive waves are generated -characterized by choppiness and waves moving many directions

gravity waves

as more energy is transferred to the ocean these develop, which are symmetric waves that have wavelengths exceeding 1.74 cm. during this stage gravity replaces capillary as the dominant restoring force -length is generally 15 to 35 times the height -as additional energy is gained, wave height increases more rapidly than wavelength→crest becomes pointed and troughs are rounded resulting in trochoidal waveform -when wave speed equals wind speed, neither height nor length can change

circular orbital motion

as the wave travels, the water passes the energy along by moving in a circle. When observing an object floating on a wave you will see it move up and backward, up and forward, down and forward, down and backwards. So it moves in a circle -the circular orbits of an object floating at the surface have a diameter equal to the wave height

wave refraction

because waves rarely approach shore at a perfect right angle, some waves feel bottom before others. This is called the bending of each wave crest.

standing waves

can be produced when waves are reflected at right angles to a barrier. Sum of two waves with the same wavelength moving in opposite direction, resulting in no net movement.

restoring force

capillary, property that results from surface tension of water, is the dominant restoring force that works to destroy these tiny waves, sectoring the smooth ocean surface again

Internal waves

created by the movement of water of different densities. -Can be much larger than surface waves, for example 100 meters, but they are not as energetic -Can be created by tidal movement, turbidity currents, wind stress or pass ships

shoaling process

decreases because shoaling depths interfere with water particle movement at the base of the wave. As it slows down, the following waveform is traveling at the original speed so there is a decrease in wavelength. Some energy is lost to friction, but the rest increases the wave height. The increase in height and decrease in wavelength causes a increase in wave steepness so that when it reaches 1:7 ratio it breaks surf. -surf from distant storms, breakers will develop near shore in shallow water -surf from local wind, will not be less sorted and will break shortly after feeling bottom a distance from shore When the water depths is about one and one third times the wave height, the crest of the wave breaks, producing surf When the water depth is less than 1/20 the wavelength the wave in the surf zone behaves as shallow water waves, but at the surface the individual orbiting particles have not been slowed down—this results in the top part overrunning the bottom part

wave height

designated by symbol H, is the vertical distance between crest and trough

orthogonal lines

drawn perpendicular to the wave fronts and are spaced so that energy between lines is equal at all times -converge on headlands and diverge in days -meaning wave energy is concentration on headlands and dispersed in bays→erosion at H and sediment deposition at B

shoaling

effect by which surface waves entering shallower water increase in wave height

transverse waves

energy travels at right angles to the direction of the vibrating particles. Ex. Like shaking a taught rope -generally these type of waves only transmit through solids because the particles in solids are bound to one another more strongly, enough to transmit this kind of energy -type of body wave

fully developed seal

equilibrium condition where waves cannot grow because they loss as much energy breaking as whitecaps under the force of gravity as they receive from the wind.

tides

gravitational pull of the Moon and Sun create vast, low, highly predictable waves

still water level

half-way in between the crest and trough; zero energy level; no waves here

plunging breaker

has a curling crest that moves over an air pocket, occurs because particles in the crest literally overrun the wave. Form on moderately steep beach slopes

crest

high part of the wave

wavelength

horizontal distance between any two corresponding points on successive waves, like crest to crest or trough to trough

deep water waves

if the water depth (d) is great than the wave base (L/2) -deep-water waves have no interference with the ocean bottom, so they include all wind-generated waves, where the water depths far exceed the wave base

troughs

low part of the wave

surf zone

margin of continents, zone of breaking waves

splash waves

mass movements into the ocean like calving icebergs etc

rouge waves

massive, solitary waves that can reach enormous height and often occur at ties when normal ocean waves are not unusually large -in the open ocean, one wave in 23 will be over twice the height of the wave average, one in 1175 will be three times, and one in 300,000 will be four times -chances of a truly monstrous wave are one in several billion -main cause theorized to be extraordinary case of constructive wave interference when multiple waves overlap in phase to produce an extremely large wave "wild coast" off the southeast coast of Africa where the Agulas current flows directly against large Antarctic storm waves, creating rogue waves. Stretch of water is probably responsible for sinking more ships than any other place of earth

Atmospheric waves

movement of different air masses creates this, which are often represented by ripple-like clouds in the sky. Common when cold fronts invade an area

orbital waves

movement of particles in ocean water involves components of both types so particles move in circular orbits

frequency

number of wave crests passing a fixed location per unit of time and is the inverse of the period f=1/ period (T)

constructive interference

occurs when the wave trains having the same wavelength come together in phase, meaning the crest to crest and trough to trough. -waves with same wavelength but H equal to the sum of individual wave heights

destructive interference

occurs when wave trains having the same wavelength come together out of phase, if the waves have identical heights the sum is zero→cancel each other out

surging breaker

ocean bottom has an abrupt slope, the wave energy is compressed into a shorter distance and the wave will surge forward

forced wave

one that is maintained by a force that has periodicity coinciding with the period of the wave -for most waves the force in wind or tides

Tsunami

originate from the sudden changes in the topography of the sea floor caused by slippage along underwater faults, underwater avalanches or volcanic eruptions -faults that produce vertical displacement (uplift or downlift) change the volume of the ocean basic and affects the entire water column -wavelength of typical tsunami is 200 kl and can move 700 kl per hour and only .5 meters tall -when it hits shore it is more like a storm surge than a wave -can cause the sea to rise over 40 meters more than usual -typically a series of waves -86% generated in pacific -krakatau eruption→devastated sunda strait -generally earthquakes less than 6.5 are not tsunamigenic

capillary waves

pressure and stress from wind blowing over the ocean surface deform it into small, rounded waves with V-shaped troughs and wavelengths less than 1.74 cm

interference patters

produced when two or more wave systems collide. Sum of the disturbance that each wave would have produced individually. -when this happens the pattern may be constructive or destruction of mixed

spilling breaker

result from gently sloped ocean bottom, which extracts energy from the wave more gradually, producing a turbulent mass of air and water than runs down the front slop of the wave instead of producing a cresting curl

wave diffraction

results from the wave energy being transferred around or behind barriers. Occurs because any point on a wave front is a source from which energy can propagate in all directions

wave trains

slower shorter groups

wave base

the depth at which the circular orbit become so small that movement is negligible = one-half wavelength measured from still water level (L/2) -thus the longer the wave, the deeper the wave base

decay distance

the distance over which waves change from choppy "sea" to uniform swell

Disturbing forces

the energy (or disturbance) that causes ocean waves to form. Ex. movement of fluids with different densities Air-water interface Air-air interface Water-water interface

longitudinal waves

the particles that virbrate "push and pull" in the same direction the energy is traveling, like a spring whose coils are alternately compressed and expanded (ex. Sound moves this way)

Wave dispersion

the sorting of waves by their wavelength

wave period

time it takes for one full wave-or wavelength-to pass a fixed position -typically between 6 and 16 seconds

mixed interference

two swells consisting of waves of various heights and lengths producing a mixture of constructive and destructive. Creates varied sequence of high and low waves

Swell

uniform, symmetrical waves that have traveled out of the area they originated. Generated when they move toward the margins, winds speed diminish and the waves move faster than the wind caused their steepness to decrease and become long-crested waves -waves with longer wavelengths travel faster, followed by wave trains

wave steepness

wave height (H)/ wavelength(L) -if the wave steepness exceeds 1/7 the wave breaks (spills forward) because the wave is too steep to support itself

free wave

wave moving with the momentum and energy imparted to it in the sea area but it is not experiencing a maintaining force that keeps it in motion ex. Swell

wave speed

wavelength/ period -more correctly known as celerity, no mass in in motion, just the wave form -speed is dependent on (1) wavelength (2) several other variables such as gravitational attraction that remain constant on earth -the longer the wavelength the fast the wave travels

shallow-water waves

waves in which depth is less than 1/20 of the wavelength. -they touch or feel the bottom b/c the ocean floor interferes which their orbital motion -speed in influenced by gravitational acceleration and the water depth -gravitational acceleration remains constant on earth so the equation for wavespeed is S (in meters per second) = 3.13 square root of d in meters -deeper the water the faster the wave travels ex. Tides and tsunamis -particle motion is shallow-water waves is in a very flat elliptical orbit that approaches horizontal oscillation

transitional waves

waves that have some characteristics of shallow-water waves and deep-water waves -wavelength between two times and 20 times the water depth

progressive waves

waves that oscillate uniformly and progress or travel without breaking. They may be longitudinal, transverse or a combination called orbital