Chapter 8: Waves and Water Dynamics

wave generation

wave generation

all begin as disturbances (releases of energy), wind, density diff, mass movement, gravity, human activities,

air ocean interface

ocean waves

air air interface

atmospheric waves (ripple like clouds)

water water interface

internal waves

internal waves

associated with pycnocline, change of density, results in change of temp, larger than surface waves, caused by tides, turbidity currents, winds, ships

wave movement

waves transmit energy, cyclic motion of particles in ocean. move up down, back forth, around + around

progressive waves

oscillate uniformly and progress without breaking (longitudinal, transverse, orbital)

longitudinal waves

particles move back and forth in direction of energy transmission, and waves can transmit matter through solids, liquids, gases

push pull waves, like a spring

transverse waves

particles move back and forth in a direction at right angles to direction of energy transmission, transmit energy through solids.

orbital waves

particles move in circular orbits passing through the top half of the orbit in the direction of energy transmission

wave terminology

crest (highest part), trough (lowest), still water lever (level with no wave), wave height, wavelength

wave steepness

H/L (height over wavelength)

wave period

T, time for one wavelength to pass fixed point, typical time btwn. 6-16 seconds

wave frequency

inverse of period or 1/T

circular orbital motion

travel through long distances (10,000km; ~6000miles), water doesnt travel, wave form does.

orbital wave characteristics

diameter of orbital motion decreases with depth of water, wave base = 1/2 L, hardly any motion below wave base due to wave activity.

deep water waves

wave base: depth where orbital movement of water particles stops

condition: if water depth is greater than wave base (>1/2, wave is a deep water wave)

wave speed

wavelength (L)/ period (T)

wave speed

celerity (C)

shallow water waves

water depth is less than 1/20 L, long waves.

transitional waves

have characteristics of both deep and shallow water waves, celerity depends on both water depth and wavelength

capillary waves

wind generates stress on sea surface (v shaped troughs) wavelengths less than 1.74 cm (.7 in)

ripples, wind generates initial stress on sea surface

gravity waves

increasing wave energy, pointed crests, rounded troughs, wavelengths greater than 1.74 cm

more energy transferred to ocean, trochoidal waveform as crests become pointed

sea

where wind driven waves are generated, sea area

factors affecting wave energy

wind speed, wind duration, fetch (distance over which wind blows in one direction)

wave height

usually <2 m, 6.6 feet. breakers called whitecaps form. Beaufort wind scale describes appearance of sea surface.

USS Ramapo

1933, 152 m (500 ft) wave hit it in Pacific typhoon

fully developed sea

equilibrium condition, waves can’t grow more

swell

uniform symmetrical waves that travel outward from storm area. doesn’t particularly imply a specific wave size.

wave train

a group of waves with slower, shorter characteristics

wave dispersion

sorting of waves by wavelengths

decay distance

distance over which waves change from choppy sea to uniform swell (can be up to several hundred km)

constructive interference

in phase wave trains with about the same wavelengths, crest to crest and trough to trough, addition, height equals to sum of individual waves

destructive interference

out of phase wave trains, with same wavelengths crest to trough, cancel eachother

mixed interference

two swells with diff wavelengths and diff wave heights

rogue waves

spontaneous, solitary ocean waves, In a sea of 2 m (6.5ft) waves a 20 m(65ft) rogue wave may appear. superwaves, monster waves, sleeper waves or freak waves. 10 large ships lost every year, up to 1000 smaller vessels

surf zone

zone of breaking waves near shore

shoaling water

water becoming gradually more shallow, When deep water waves encounter shoaling water less than ½ their wavelength, they \n become transitional waves

what happens when a deep water wave approaches shore

speed, wavelength, height, steepness decreases

three types of breakers

spilling, plunging, surging

spilling breakers

gently sloping sea floor, wave energy expended over long distance, water slides down front slope of wave, low wave energy, longer life span

plunging breakers

moderately steep sea floor, curling wave crest, wave energy expended over shorter distance, best for surfers

surging breakers

steepest sea floor, energy spread over shortest distance, body surfing, break on shore

wave refraction

waves rarely approach shore at 90 degree angle, as they approach, they refract, so wave crest parallel to shore. wave speed is proportional to depth of water.

orthogonal lines

or wave rays, drawn perpendicular to wave crests. more energy released on headlands, energy more dissipated in bays

stationary waves

two waves with same wavelength moving in opp. directions, water sloshes back and foth, nodes have no vert. movement, antinodes are alternating crests and troughs, points of greatest vertical movement.

tsunami

seismic sea waves, caused by earthquake, landslides underwater, volcanoes collapsing underwater, eruptions underwater, meteor splashes

tsunami vs wind generated waves

wind generated waves in open ocean are deep water waves that don’t feel sea floor, but tsunami in even deeper water act as shallow water waves that encompass entire water column

tsunami destruction

40 m, 131 feet high at shore

where do most tsunamis occur

in pacific ocean, hawaii, indonesia, alaska, new guinea, japan

tsunami warning systems

Pacific tsunami warning center (PTWC) honolulu hawaii,

deep ocean assessment and reporting of tsunami

DART: system of buoys, detects pulse of tsunami passing

tsunami watch

issued when potential for tsunami exists

tsunami warning

unusual wave activity verified, evacuate people, move ships

wave energy

LIMPET: Land Installed Marine Powered Energy Transformer: coast of scotland