Geography and Oceanography - Chapter 17 pps

Waves in the Ocean
Waves in the Ocean


Words from these PPT slides are
Words from these PPT slides are
already on the course web site.
already on the course web site.
Wave Parameters
Wave Parameters
Properties of Ocean Waves
Properties of Ocean Waves
❥
An ocean wave is an undulation of the sea
An ocean wave is an undulation of the sea
surface.
surface.
–
Wave crest
Wave crest
–
Wave trough
Wave trough
–
Wave height
Wave height
–
Wave length
Wave length

–
Wave period
Wave period
❥
Progressive waves
Progressive waves


move across the sea surface.
move across the sea surface.
❥
Standing waves
Standing waves


oscillate about a fixed point.
oscillate about a fixed point.
What Causes Waves?
What Causes Waves?
❥
Wind
Wind
❥
Submarine disturbance
Submarine disturbance
❥
Gravitational attraction of sun and
Gravitational attraction of sun and
moon
moon

Wind Generation of Waves
Wind Generation of Waves
❥
Wind velocity
Wind velocity
❥
Wind duration
Wind duration
❥
Fetch (distance over which wind blows)
Fetch (distance over which wind blows)
❥
Simply put, wave size
Simply put, wave size
increases
increases
as all
as all
these factors
these factors
increase
increase
.
.
Progressive Waves
Progressive Waves
❥
Wind-generated waves are
Wind-generated waves are
progressive

progressive
waves
waves


because they travel across the sea
because they travel across the sea
surface.
surface.
Progressive Wave Types
Progressive Wave Types
❥
Sea
Sea
- irregular waves in the area of
- irregular waves in the area of
generation
generation
❥
Swell
Swell
- more regular waves beyond area
- more regular waves beyond area
of generation
of generation
❥
Surf
Surf
- waves that have reached the coast,
- waves that have reached the coast,

grow in height, and break
grow in height, and break
Wave Motions
Wave Motions
❥
Forward
Forward
movement of the wave form.
movement of the wave form.
❥
Orbital
Orbital
motion of water particles
motion of water particles
beneath
beneath


the wave.
the wave.
❥
It is
It is
wave energy
wave energy
,
,


NOT water molecules,

NOT water molecules,
that moves across the sea surface.
that moves across the sea surface.
Flow of Energy, not Mass
Flow of Energy, not Mass
Wave Motion with Depth
Wave Motion with Depth
Motion Animation
Motion Animation
Deep Water Waves
Deep Water Waves
Waves do NOT interact with the seafloor.
Waves do NOT interact with the seafloor.
Orbits of the water molecules are
Orbits of the water molecules are
circular
circular
.
.


Shallow Water Waves
Shallow Water Waves
Waves DO interact with the seafloor.
Waves DO interact with the seafloor.
Orbits of the water molecules become
Orbits of the water molecules become
elliptical
elliptical
.

.
Life History of Ocean Waves
Life History of Ocean Waves
Life History of Ocean Waves
Life History of Ocean Waves
❥
Waves originate in the fetch area.
Waves originate in the fetch area.
This area is characterized by a
This area is characterized by a
“confused” sea state with extensive
“confused” sea state with extensive
wave interference.
wave interference.


This interference
This interference
may be
may be
–
Constructive
Constructive
–
Destructive
Destructive
Rogue Waves?
Rogue Waves?
❥
Constructive wave

Constructive wave
interference -
interference -
wave
wave
buildup
buildup
Rogue Waves
Rogue Waves

Destructive Waves
Destructive Waves
❥
Destructive wave
Destructive wave
interference -
interference -
wave
wave
cancellation
cancellation
Progressive Wave Types
Progressive Wave Types
❥
Sea
Sea
- irregular waves in the area of
- irregular waves in the area of
generation
generation

❥
Swell
Swell
- more regular waves beyond area
- more regular waves beyond area
of generation
of generation
❥
Surf
Surf
- waves that have reached the coast,
- waves that have reached the coast,
grow in height, and break
grow in height, and break
Transformation of Deep-water Waves:
Transformation of Deep-water Waves:
Dispersion
Dispersion
Shallow Waves Affected by
Shallow Waves Affected by
Bottom
Bottom
❥
In shallow water, the sea bottom
In shallow water, the sea bottom
transforms the wave’s properties.
transforms the wave’s properties.
This leads to
This leads to
wave refraction

wave refraction


and
and
waves collapse forming
waves collapse forming
surf
surf


(breakers).
(breakers).
❥
Bending of the
Bending of the
wave crest as
wave crest as
waves enter
waves enter
shallow water. It
shallow water. It
is due to
is due to
–
Drag along the
Drag along the
bottom.
bottom.
–

Differential
Differential
speed along the
speed along the
crest.
crest.
Wave Refraction
Wave Refraction
Refraction Animation
Refraction Animation
Shallow-water Wave
Shallow-water Wave
Transformations
Transformations
❥
Interaction with the sea bottom.
Interaction with the sea bottom.
❥
Bottom friction alters both the
Bottom friction alters both the
–
Wave form
Wave form
❥
Wavelength shortens (decreases)
Wavelength shortens (decreases)
❥
Height increases
Height increases
–

Celerity (speed of wave form)
Celerity (speed of wave form)
❥
decreases
decreases
Transformation of Shallow-water Waves
Transformation of Shallow-water Waves