Oceanography: Waves – Flashcards
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What do waves transmit across the ocean's surface?
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Energy (not mass)
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What is a wave orbit; give an example?
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waves travel ahead, but the objects on the surface do not move; a gull wading in the ocean will not move forward, only the wave will move
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What is the highest point of a wave called?
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Crest
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What is the lowest point of a wave called?
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Trough
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What it the distance between the crest and trough called?
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Wave Height
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What is the distance between two crests, or two troughs called?
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Wavelength
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What is it called when you measure the number of wave crests passing a point A each second?
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Wave Frequency
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What is it called when you measure the time required for a wave crest at point A to reach a later point B?
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Wave Period
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How does the orbital motion change with depth?
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As they descend they become smaller because of the friction
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What depth is when you no longer have the wave orbitals?
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A depth of 1/2 the wavelength of the wave
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How does wavelength affect wave orbitals?
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Wavelength determines the size of orbitals
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How does water depth affect wave orbitals; how?
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Water depth determines the shape of the orbitals; deep water: circular orbitals, shallow water: elliptical orbitals
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What are the types of waves?
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Wind, Seiche, Tsunami, and Tide
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Which of the four wave types are free waves?
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Wind, Seiche and Tsunami
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Which of the four wave types are forced waves?
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Tide
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What are free waves?
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If the disturbing force is removed the waves will still move energy across the ocean
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What are forced waves?
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If the disturbing force is removed the wave will not move energy across the ocean
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What is the typical wavelength of a wind wave; what is the disturbing force for a wind wave?
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60-150m; wind over ocean
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What is the typical wavelength of a seiche wave; what is the disturbing force for a seiche wave?
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Variable but usually a fraction of the basin size; Changes in atmospheric pressure, storm surge, etc
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What is the typical wavelength of a Tsunami wave; what is the disturbing force for a tsunami wave?
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200 km; Seafloor fault, volcanic eruption, landslide
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What is the typical wavelength of a tidal wave; what is the disturbing force for a tidal wave?
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1/2 of the Earth's circumference; Gravitational attraction and Earth rotation
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Which wave type is the most efficient at moving energy?
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Wind waves
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Which wave type is the least efficient at moving energy?
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Capillary waves (part of wind waves), then tsunami's
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Which type of waves are deep water waves?
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Capillary and wind waves
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What are the characteristics of deep water waves?
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Waves move through water whose depth is > 1/2 wavelength, have circular orbitals
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What are the characteristics of shallow water waves?
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Waves move through water whose depth is < 1/2 wavelength, have flattened, elliptical orbitals
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How fast will a longer wavelength be compared to a shorter wavelength?
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The long wavelength will be faster
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What causes capillary waves?
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Frictional resistance (Capillary waves are the ripple looking waves)
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What is constructive interference?
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When the crests of two waves line up, and the amplitude is doubled
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What is destructive interference?
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When the crest and trough of two waves line up and are cancelled out
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Which waves are the dangerous ones: constructive or destructive?
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Constructive. They are also called rogue waves
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How big is the biggest wave ever recorded?
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34m in height with a wavelength of 360m
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When it is winter in the Northern hemisphere, where is there a lot of ocean wave activity
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In the Northern hemisphere, as the higher latitudes get colder, driving atmospheric circulation to transfer more energy to the ocean surface
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When it is summer in the Northern hemisphere, where is there a lot of ocean wave activity?
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In the Southern hemisphere (where it is winter)
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What happens to the fetch of a wave when the wind speed increases?
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The fetch also increases
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Describe how sea changes to swell
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Wind blows over area of fetch which develops ripples. At the end of this fetch are the largest waves, these waves have such large wavelengths in the sea that the energy moves faster and can reach the shores which is the swell
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Why do waves break?
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The wave is too high for the wavelength it has, the wave orbitals begins to flatten from circular to ellipses which cause the waves to turn over on themselves
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Why do waves refract off the shore?
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As waves come into the shore, the are acting like deep waves in the middle but they become shallower which cause them to break toward the shore
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What are internal waves?
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waves that are beneath the surface of the ocean, that has different density than the wind surface waves
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What happens in a seiche wave?
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Wind stops, water sloshes back and forth at the basins node which produces a "standing wave"
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Can energy be added to seiche waves; if so how?
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Yes; energy can be add rhythmically and if added at the right moment the seiche will get bigger and bigger
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Where can seiches happen?
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In bays and harbours of the ocean, and lakes
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What are some characteristics of tsunami waves?
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Shallow water waves that have long wavelengths, meaning they're fast, these waves are seismic generated waves that happen from 5-20 minutes
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What is the first part of a tsunami to hit land?
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The trough
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Where should you head if there is a tsunami?
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If you have a boat and can get out before the crest hits then go out into the ocean as you will not feel the tsunami. If you don't, head for the highest ground
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What seismic activity will result in the worst damaging tsunami?
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A megathrust earthquake when and overriding plate unlocks from the subjecting plate
