Waves Flashcards
A disturbance or oscillation that travels to a matter or space accompanies by a transfer of energy. Can carry energy from one place to another, as a medium they are like a harmonic oscillator, they require a “restoring force” and inertia.
Waves
Propagate along a surface or interface
Surface Waves
Caused by energy passing through the water, causing the water to move in a circular motion. A progression of energy from one point to another and does no move forward, only the energy in it progresses.
Waves
Visual proof of the transmission of energy across the surface of the ocean.
Ocean Waves
Anatomy of a Wave:
- Highest point in the wave
- Lowest point in the wave
- Vertical distance between the wave crest and the wave trough
- Water displacement from its undisturbed state. Always one-half the wave height (at least for a symmetric wave).
- Distance from one crest to the next crest or from one trough to the next trough.
- Crest
- Trough
- Wave Height
- Wave Amplitude
- Wavelength
Defined as wave height divided by wavelength (S = H/L). Therefore, the same wave height will result in high steepness if the wavelength becomes smaller.
Wave Steepness
Number of wave crests passing point A, each second.
Wave Frequency
Time Required for the wave crest at point A to reach point B
Wave Period
Half of the wave height
Amplitude
Waveheight divided by wavelength (H/L)
Steepness
Causes waves to form
Disturbing Force
Interface of Fluids with Different Densities:
- Air-ocean interface
- Air-air interface
- Water-water interface
- Ocean Waves
- Atmospheric Waves
- Internal Waves
Acts on a water particle displaced from its equilibrium position
Restoring Force
Type of Wave:
- <1 Second, <2 Cm
- 1-10 Sec, 1-10 m
- 10-30 Sec, up to 100 m
- 5-90 minutes, 20 km to 300+ km
- Capillary or Ripple
- Chop
- Swell
- Tsunami
Source of Types of Waves:
- Winds
- Gravity (Tides)
- Discontinuity in Ocean Surface
*Earthquake (Tsunamis)
*Landslides
*Rain Drops
Most Ocean Waves Generated by Winds:
- Ripples, Wind generates initial stress on sea surface
- More energy transferred to ocean, Trochoidal waveform as crests become pointed
- Any wave that has moved out of its wind generation source region
- Capillary Waves
- Gravity Waves
- Swell
Wave size depends on the:
- The area over which the wind is blowing
- The speed at which the wind is blowing
- How long the wind has been blowing
- Fetch
- Wind Velocity
- Duration
Equilibrium Condition, waves can grow no further
Fully Developed Sea
Uniform, symmetrical waves that travel outward from storm area, long crests, transport energy long distances
Swell
As waves move beyond ___, wind speed ____ and waves move ____ than wind. Wave Steepness ____ and waves become ______ waves.
Fetch, Decreases, Faster, Decreases, Long-Crested
Factors Affecting Wave Energy:
*
*
* Distance over which wind blows
- Wind Speed
- Wind Duration
- Fetch
Waves:
Stage 1: ?
Stage 2: ?
Stage 3: ?
Capillary Waves (CM Scale)
Wind Waves
Mature Sea - Swell
Directly related to wave energy and is usually less than 2 meters.
Wave Height
Breakers called ____ form when wave reaches critical steepness.
Whitecaps
Describes appearance of sea surface
Beaufort Wind Scale
A standing wave that oscillates back and forth within a water body. Water sloshes back and forth, and the wave decreases in size due to friction as its oscillation tries to reach equilibrium. Most often, generated by a persistent strong wind blowing down the long axis of a large water body. When the wind subsides, the water is released as a _____ wave. Can also be generated by a disturbance such as an earthquake, landslide, wave interaction, changes in air pressure, or changes of wind.
Seiche
A Series of long-period waves (on the order of tens of minutes) that are usually generated by an impulsive disturbance that displaces massive amounts of water, such as an earthquake occurring on or near the sea floor. Underwater volcanic eruptions, landslides beginning above the water level, and large pieces of falling ice can also cause a ____. They are seismic sea waves. If it comes from a meteorite impact, can also be called ______.
Tsunami, Splash Waves
- Long wavelengths (>200km or 125 miles)
- Behaves as a shallow-water wave
- Encompasses entire water column, regardless of ocean depth.
- Can pass undetected under boats in open ocean
- Speed proportional to water depth
- Very fast in open ocean
Tsunami
Historically where the largest tsunami happened.
Nicaragua
Uses Seismic wave recordings to forecoast tsunami, coordinates information from 25 Pacific Rim countries, with headquarters in Hawaii
Pacific Tsunami Warning Center (PTWC) - Honolulu, HI
- System of Buoys
- Detects pulse of tsunami passing
Deep Ocean Assessment and Reporting of Tsunami (DART)
- Issued when potential for tsunami exists
- Unusual wave activity Verified
- Evacuate People
- Move ships from harbors into deep waters
- Tsunami Watch
- Tsunami Warning
- Associated with Pycnocline
- Larger than surface waves
- Caused by tides, turbidity currents, winds, ships
- Possible hazard for submarines
Internal Waves
Among the largest observed internal waves anywhere in the ocean (location)
Luzon Strait
Oscillate uniformly and progress without breaking
- (1)
- (2)
- (3)
Progressive Waves:
- Longitudinal (1)
- Transverse (2)
- Orbital (3)
Also called push-pull waves, compress and decompress as they travel, like a coiled spring. Hands clapping or thumping a table, particles move back and forth in the direction of energy transmission and these waves transmit energy through all states of matter.
Longitudinal Waves
Also called side-to-side waves, energy travels at right angles to direction of moving particles, generally only transmit through solids, not liquids. A rope attached to a wall, particles move back and forth at right angles to the direction of energy transmission, these waves transmit energy only through solids.
Transverse Waves
Also called interface waves, waves on ocean surface, combination of progressive and longitudinal waves. The movement of water waves, particles move in a circular path, these waves transmit energy along interface between two fluids of different density (liquids and/or gases).
Orbital Waves
Water particles move in circle, movement up and down and back and forth.
Circular Orbital Motion
Orbital Wave Characteristics
- H/L, if it is greater than 1/7, wave breaks
- Time for one wavelength to pass fixed point, range between 6 and 16 sec
- Inverse of period or 1/T
- Wave Steepness
- Wave Period
- Wave Frequency
Diameter of orbital motion ____ with depth of water. Wave base is equal to ____. The ____ the wave, the ____ the wave base.
Decreases, 1/2L, Longer, Deeper
Types of waves defined by water depth:
- Deep-water wave
- Intermediate-water wave
- Shallow-water wave
____ is the velocity of the wave form, not the water. The ____ of a group of waves all travelling at the same speed in the same direction is less than the speed of the waves within the group. Has the equation: C = L/T
Celerity
Depth where orbital movement of water particles stops. If water depth is greater than wave base (>=1/2 L), wave is a _______. Lack of orbital motion at depth useful for floating runways and other structures.
Wave Base, Deep Water Wave
Wavelength (L) / Period (T)
Speed is called ____. It is proportional to wavelength. For _____, long waves are fast waves.
Wave Speed, Celerity, Deep-water waves
The ____ the wavelength, the ____ the speed.
Longer, Faster
Water depth is <= (1/20L), ____ is proportional to depth of water. For ______, the _____, the _____ the wave.
Shallow-water waves, Celerity, Shallow-water waves, Deeper, Faster
Characteristics of both deep and shallow-water waves. ____ Depends on both water depth and wavelength.
Transitional Waves, Celerity
Waves in ______ are large because of prevailing _____.
Southern Hemisphere, Westerlies
Collision of two or more wave systems
Wave Interference
In-phase wave trains with about the same wavelengths
Constructive Interference
Out-of-phase wave trains with about the same wavelengths
Destructive Interference
Two swells with different wavelengths and different wave heights
Mixed interference
Difficult to forecast
Occur more near weather fronts and downwind of islands
Strong ocean currents amplify opposing Swells
Also called superwaves, monster waves, sleeper waves or freak waves.
Crests are mountains of water, troughs are holes in the sea.
Rogue Waves
Massive, spontaneous, solitary ocean waves and can reach abnormal heights, enormous destructive power
Rogue Waves
Zone of breaking waves near shore
Surf Zone
Water becoming gradually more shallow, when deep water waves encounter _____ less than 1/2 their wavelength, they become _____.
Shoaling Water, Transitional Waves
As a deep water wave becomes a shallow water wave:
- Wave speed decreases
- Wavelength decreases
- Wave height increases
- Wave steepness (Height/Wavelength) increases
- When steepness >= 1/7, wave breaks
Navigators have long known that ______ indicate dangerously shallow water. There could be presence of shallowly submerged obstacle such as coral reef, sunken wreck, or sand bar.
Breaking Waves
- Water slides down front slop of wave, wave breaks far from shore, wave energy expended over longer distances
- Wave curls over forming a tunnel until wave breaks, wave energy expended over shorter distances, best for board surfers
- Wave doesn’t break until close to shore, rolls onto steep beach, energy expended over shortest distance, “destructive”.
- Spilling Breakers
- Plunging Breakers
- Surging Breakers
- Bending of Waves
- Bouncing back of waves
- Radiating Outward of waves
- Refraction
- Reflection
- Diffraction
Wave energy unevenly distributed on shore
Wave Refraction
_____ or wave rays - drawn perpendicular to wave crests.
- more energy released on headlands, energy more dissipated in bays
- large waves at headlands, area of surfing and erosion
- smaller waves at bays, area for boat anchorage and sediment deposition
Orthagonal Lines
Gradually erodes headlands, sediment accumulates in bays
Wave Refraction
Waves and wave energy bounced back from barrier, reflected wave can interfere with next incoming wave, with constructive interference, can create dangerous plunging breakers
Wave Reflection
Occurs when an object (island) causes a wave to change direction and bend around it. (i.e. Ocean waves change direction as they pass a group of islands)
Diffraction
