Lecture `19- Ocean Waves Part 2 - PHYS OCE

7 new waves

1. stokes wave and breaking waves

2. capillary waves

3. wind-driven waves

4. coastal waves'

5. standing waves

6. tsunamis

7. internal waves

three previous wave types talked about

shallow water waves and deep water waves and surface gravity waves

when do stokes and breaking waves occur

when waves get steeper

when do capillary waves occur

when waves are affected by surface tension

when do wind-driven waves occur

when surface friction occurs at the surface

when do coastal waves occur

when interaction with the coast is considered

when do standing waves occur

when waves are reflected from boundaries

when do tsunamis occur

example of short water waves

when do internal waves occur

when density is not constant

what does waves looking line sine/cosine assume

no net transport because the particles are moving in a closed circle

stokes drift

particle motion is not a closed circle and therefore has net transport

why are stokes waves not sinusoidal

because they are large steep waves close to breaking meaning they are not closed circles

stoke waves morphology

long and smooth trough with a short steep crest

how do stokes waves work

when waves become steeper they move faster and have a net transport in direction of wave propogation

phase speed equation of stokes waves

C = sqrt((gL/2𝝅)[1+𝝅²(H/L)²])

why is the motion of particles not circular

faster forward motion near crest wave and slower motion near flat trough of wave

where in the depth of a wave is it faster and slower

faster at the top so we get a net transport forward of our BIRD

breaking waves

waves break when steepness H/L ~ 1/7 or H/h ! 0.8

process of breaking waves

1. front of waves slow down

2. waves get steeper

   1. they break and spill over

factors affecting breaking type waves

size and length of waves, bottom slope steepness

what happens when the bottom is steeper in waves

waves grow faster and waves become steeper = plunging breaker

best waves for surfing

plunging breaker

spilling breaker wave

flat bottom

surging breaker

very steep bottom

capillary waves

small waves of a few centimeters superimposed on larger waves or flat water

what are capillary waves generated by

wind blowing and surface tension

what length of capillary waves move faster

shorter, which is opposite to gravity waves

is group speed or phase speed faster for capillary waves

group speed (opposite of gravity waves)

what do capillary waves do

make surface rough and affect wind stress

what does propagation speed of capillary waves depend on

wave length, density, surface tension

wave length formula

L = 2pi/k

propagation speed of capillary waves formula

C² = g/k + k/ρτ

fetch

wind with a particular speed blows for a particular duration over a piece of the ocean of particular length

fully developed sea

steady wave field under a storm

how do waves move away from a storm

as deep water waves

swell

long waves that reach areas far from the storm

what length waves will move faster away from storm

longer waves

deep water wave velocity equation

c = g/2pi*T

important factors of generation of deep water waves

1. wind speed

2. wind duration

   1. fetch

what do stronger winds with longer duration blowing over larger area generate

higher and longer waves

what limits maximum possible waves

wind speed, wind duration, fetch