Waves Chapter 9

Study Plan 9.1 Ocean waves move energy across the sea surface 9.2 Waves are classified by their physical characteristics 9.3 The behavior of waves is influenced by the depth of water through which they are moving

Study Plan 9.4 Wind blowing over the ocean generates waves 9.5 Interference produces irregular wave motions 9.6 Deep-water waves change to shallow-water waves as they approach the shore

Study Plan 9.8 “Tidal waves” are probably not what you think 9.9 Storm surges form beneath strong cyclonic storms 9.10 Water can rock in a confined basin 9.11 Water displacement causes tsunami and seismic sea waves

What is a wave? A Wave is a rhythmic movement that carries energy through matter or space. In oceans, waves move through seawater

Parts of the wave Crest – highest point of a wave Trough – lowest point of a wave Wave Height – vertical distance between the crest and the trough Wavelength – horizontal distance between two crests or two troughs

Wavelength Crest Wave Height Still Water Trough Wave Parts

9.1 Ocean waves move energy across the sea surface Orbit: Energy transfer from water particle to water particle Orbital wave: a wave in which particles of water move in closed circles as the wave passes progressive wave: the wave moves forward

Period and frequency Period: the time it takes for a wave to move a distance of one wavelength Frequency: number of waves passing a fixed point per second

9.2 Waves are classified by their physical characteristics Ocean waves are formed by a disturbing force (energy that causes ocean waves to form) Waves are weakened by a restoring force (returns the wave to flatness after a wave has formed in it) Wavelength is the most useful measure of a wave size

Idealized Wave Spectrum

9.3 The behavior of waves is influenced by the depth of water through which they are moving

Orbit Diameter and Stokes Drift

Wave base is the depth to which a surface wave can move water. Wave Motions Wave base is the depth to which a surface wave can move water. If the water is deeper than wave base, orbits are circular and there is no interaction between the bottom and the wave. If the water is shallower than wave base, orbits are elliptical and become increasingly flattened towards the bottom.

Deep- and Shallow-Water Motion

Celerity is the velocity of the wave form and not of the water. Wave Motions There are three types of waves defined by water depth: Deep-water wave, Intermediate-water wave, and Shallow-water wave. Celerity is the velocity of the wave form and not of the water. The celerity of a group of waves all traveling at the same speed in the same direction is less than the speed of individual waves within the group.

Celerity C = L / T Speed of the wave L = wavelength T = time or period

9.4 Wind blowing over the ocean generates waves Wind waves are gravity waves formed by the transfer of wind energy into the water

Capillary wave

Fetch is the area of contact between the wind and the water and is where wind-generated waves begin. Seas is the term applied to the sea state of the fetch when there is a chaotic jumble of new waves. Waves continue to grow until the sea is fully developed (3 days of wind) or becomes limited by fetch restriction or wind duration.

Waves Caused by Wind When wind blows across a body of water, friction causes the water to move along with the wind. Wave Height depends on – Wind speed Distance over which the wind blows Length of time the wind blows

9.5 Interference produces irregular wave motions Constructive vs. destructive interference

Wind waves can grow to enormous Size 7 Feb 1933 For days, wind was blowing at 67 MPH (107 kph)

34 m (112 ft)!!!

9.6 Deep-water waves change to shallow-water waves as they approach the shore

Wave Movement When a wave breaks against the shore, the crest outruns the trough and the crest collapses. Called a breaker. In this case, water does move forward and backward.

S Wave Refraction

S

P

S Convergence Divergence

9.8 “Tidal waves” are probably not what you think

9.9 Storm surges form beneath strong cyclonic storms

Storm surge is the rise in sea level resulting from low atmospheric pressure and the accumulation of water driven shoreward by storm winds. Water is deeper at the shore area, allowing waves to progress farther inland. Storm surge is especially severe when superimposed upon a spring high tide.

9.11 Water displacement causes tsunami and seismic sea waves “Tsunami” – “harbor wave” or seismic sea wave

Tsunami are always shallow-water wave 26 Dec 2004, Indian Ocean Wavelength: up to 200 km (125 mi) 470 MPH (212 m / s) 5 hours to get to Alaska!!!

Tides

What causes tides? The gravitational forces of the moon and sun on the water causes the tides.. The moon, being nearest, has the greatest effect even though the sun is the larger of the two. High tides are generated on the sides of the Earth nearest to and farthest from the moon

During new and full moon phases the moon, sun, and Earth are aligned causing a greater gravitational pull on the Earth. This results in higher high tides and lower low tides.

How are Tides Predicted?