Waves and Tides

Properties of Ocean Waves

• A. Waves are the undulatory motion of a water surface.

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Properties of Ocean Waves • A. Waves are the undulatory motion of a water surface.

– 1. Parts of a wave are: Wave crest, Wave trough, Wave height (H), Wavelength (L),and Wave period (T).

Properties of Ocean Waves

• B. Most of the waves present on the ocean’s surface are wind-generated waves.

Properties of Ocean Waves • B. Most of the waves present on the ocean’s surface are wind-generated waves.

– 1. Size and type of wind-generated waves are controlled by: Wind velocity, Wind duration, Fetch, and Original state of sea surface.

Properties of Ocean Waves • B. Most of the waves present on the ocean’s surface are wind-generated waves.

– 1. Size and type of wind-generated waves are controlled by: Wind velocity, Wind duration, Fetch, and Original state of sea surface.

– 2. As wind velocity increases wavelength, period, and height increase, but only if wind duration and fetch are sufficient.

Properties of Ocean Waves • B. Most of the waves present on the ocean’s surface are wind-generated waves.

– 1. Size and type of wind-generated waves are controlled by: Wind velocity, Wind duration, Fetch, and Original state of sea surface.

– 2. As wind velocity increases wavelength, period, and height increase, but only if wind duration and fetch are sufficient.

– 3. Fully developed sea is when the waves generated by the wind are as large as they can be under current conditions of wind velocity and fetch.

Wave Motions • C. Progressive waves are waves that move forward

across the surface.

Wave Motions • C. Progressive waves are waves that move forward across the surface.

– 1. As waves pass, wave form and wave energy moves rapidly forward, not the water.

Wave Motions • C. Progressive waves are waves that move forward across the surface.

– 1. As waves pass, wave form and wave energy moves rapidly forward, not the water.

– 2. Water molecules move in an orbital motion as the wave passes.

Wave Motions • C. Progressive waves are waves that move forward across the surface.

– 1. As waves pass, wave form and wave energy moves rapidly forward, not the water.

– 2. Water molecules move in an orbital motion as the wave passes.

– 3. Wave base is the depth to which a wave can move water.

Wave Motions – 4. If the water is deeper than wave base, orbits are

circular and there is no interaction between the bottom and the wave, but if the water is shallower than wave base, orbits are elliptical and become increasingly flattened towards the bottom.

Wave Motions – 5. If the wave base interacts with the ocean floor, the

wave will break.

Life History of Ocean Waves • D. Wave interference is the momentary interaction

between waves as they pass through each other. Wave interference can be constructive or destructive.

Which is constructive and which is destructive?

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CONSTRUCTIVE! DESTRUCTIVE!

Other Types of Waves

• E. Internal waves form within the water column on the pycnocline.

Other Types of Waves • G. Internal waves form within the water column on the pycnocline.

– 1. Because of the small density difference between the water masses above and below the pycnocline, wave properties are different compared to surface waves.

Other Types of Waves • G. Internal waves form within the water column on the pycnocline.

– 1. Because of the small density difference between the water masses above and below the pycnocline, wave properties are different compared to surface waves.

– 2. These internal waves are slower and much larger than surface waves.

Quiz Review

Describe the following, either with a picture or with words:

1. Wave Interference 2. Wavelength 3. Wave Base 4. Crest 5. Progressive Wave 6. Wave Height

7. Internal Wave 8. Trough 9. Fetch 10.Fully Developed Sea 11.Wave Motion 12.Wave formation

Other Types of Waves

• F. Tsunamis were previously called tidal waves, but are unrelated to tides.

– 1. Tsunamis consist of a series of long-period waves characterized by very long wavelength (up to 100 km) and high speed (up to 760 km/hr) in the deep ocean.

Other Types of Waves • F. Tsunamis were previously called tidal waves, but are unrelated to tides.

– 1. Tsunamis consist of a series of long-period waves characterized by very long wavelength (up to 100 km) and high speed (up to 760 km/hr) in the deep ocean.

– 2. Because of their large wavelength, tsunamis are shallow-water to intermediate-water waves as they travel across the ocean basin.

Other Types of Waves • F. Tsunamis were previously called tidal waves, but are unrelated to tides.

– 1. Tsunamis consist of a series of long-period waves characterized by very long wavelength (up to 100 km) and high speed (up to 760 km/hr) in the deep ocean.

– 2. Because of their large wavelength, tsunamis are shallow-water to intermediate-water waves as they travel across the ocean basin.

– 3. They only become a danger when reaching coastal areas where wave height can reach 10 m.

Other Types of Waves • F. Tsunamis were previously called tidal waves, but are unrelated to tides.

– 1. Tsunamis consist of a series of long-period waves characterized by very long wavelength (up to 100 km) and high speed (up to 760 km/hr) in the deep ocean.

– 2. Because of their large wavelength, tsunamis are shallow-water to intermediate-water waves as they travel across the ocean basin.

– 3. They only become a danger when reaching coastal areas where wave height can reach 10 m.

– 4. Tsunamis originate from earthquakes, volcanic explosions, or submarine landslides.

Tides

Tidal Characteristics • A. Tides have a wave form, but differ from other

waves because they are caused by the interactions between the ocean, Sun and Moon.

Tidal Characteristics • A. Tides have a wave form, but differ from other waves because they are caused by the interactions between the ocean, Sun and Moon.

– 1. Crest of the wave form is high tide and trough is low tide.

– 2. The vertical difference between high tide and low tide is the tidal range.

Tidal Characteristics

–3. Tidal period is the time between consecutive high or low tides and varies between 12 hrs 25 min to 24 hrs 50 min.

Tidal Characteristics – 3. Tidal period is the time between

consecutive high or low tides and varies between 12 hrs 25 min to 24 hrs 50 min.

–4. There are three basic types of daily tides defined by their period and regularity: Diurnal tides, Semidiurnal tides, and Mixed tides.

Tidal Characteristics – 5. Over a month the daily tidal ranges vary systematically

with the cycle of the Moon.

– 6. Tidal range is also altered by the shape of a basin and sea floor configuration.

Origin of the Tides

• B. Tides result from gravitational attraction and centrifugal effect.

– 1. Gravity varies directly with mass, but inversely with distance.

Origin of the Tides • B. Tides result from gravitational attraction and centrifugal effect.

– 1. Gravity varies directly with mass, but inversely with distance.

– 2. Although much smaller, the Moon exerts twice the gravitational attraction and tide-generating force as the Sun because the Moon is closer.

Origin of the Tides – 3. Gravitational attraction pulls the ocean towards the

Moon and Sun, creating two gravitational tidal bulges in the ocean (high tides).

Origin of the Tides

– 4. Spring tides occur when Earth, Moon and Sun are aligned in a straight line and the tidal bulges display constructive interference, producing very high, high tides and very low, low tides.

• a. Spring tides coincide with the new and full moon.

Origin of the Tides – 5. Neap tides occur when the Earth, Moon, and Sun are

aligned forming a right angle and tidal bulges displaying destructive interference, producing low high tides and high low tides.

• a. Neap tides coincide with the first and last quarter moon.

Origin of the Tides – 6. Earth on its axis and the Moon in its orbit both revolve

eastward and this causes the tides to occur 50 minutes later each day.

Tidal Currents • C. The movement of water towards and away from

land with the high and low tides, respectively, generates tidal currents.

Tidal Currents • C. The movement of water towards and away from land with the high and low tides,

respectively, generates tidal currents.

– 1. Flood current is the flow of water towards the land with the approaching high tide.

– 2. Ebb current is the flow of water away from the land with the approaching low tide.