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Learn about the properties of ocean waves, how they are generated by wind, and their motion across the sea surface. Understand the life history of waves and how they behave in shallow and deep water. Explore the effects of bottom friction and the phenomenon of wave breaking.
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Homework Due Tuesday • Read Pages 52-55. Answer in complete sentences • What causes the Coriolis effect? • How does the Coriolis effect wind in the northern hemisphere? How is that different than its affect in the southern hemisphere? • How does the Ekman Spirial relate wind speed to water depth? • What do Gyers do? What does the book mean when it says “(Gyers) act like a giant thermostat”? • What happens when waves “pile up” ? What do you call it when they fall forward and break? Where is the wave’s energy transferred to when the wave breaks?
The oceans are in constant motion. The most obvious examples of this along the shoreline are waves. In this lecture we will learn about: • The properties of ocean waves • Wind generation of waves • Wave motion • The life history of ocean waves • Beach and shoreline processes • Waves behave like………waves
Properties of Ocean Waves Properties of Ocean Waves
Properties of Ocean Waves • An ocean wave is an undulation of the sea surface. Important wave terms to know: • Wave crest – The top of the wave • Wave trough- The bottom of the wave • Wave height-measure between crest and trough • Wavelength – measure between crests • Wave period – time it takes for a wave to move past a given point • Progressive waves move across the sea surface. • Standing waves oscillate about a fixed point.
The “top” of the wave is the • Wavelength • Crest • Trough • Period
The “bottom” of the wave is the • Trough • Crest • Wavelength • Period
The distance between the crests is the • Period • Crest • Amplitude • Wavelength
Waves are caused by different factors. • Wind • Submarine disturbances such as earthquakes or landslides (tsunamis) • Gravitational attraction of sun and moon (tides)
Wind Generation of Waves • The size and character of wind-generated ocean surface waves is determined by: • Wind velocity – Wind Speed • Wind duration – How long does it last • Fetch - distance the wind blows over the water • Simply put, wave size increases as the strength (speed) and duration of the wind, and distance over which it blows increases.
Largest recorded storm wave • height: 112 feet/34.2 m • period: 14.8 s • speed: 90 ft/s/27 m/sec = 61 mph • wavelength = 1100 ft/329 m
The distance wind blows over water is called the • Crest • Duration • Fetch • Incline
Waves height is determined by wind speed, fetch and • Direction • Temperature • Dewpoint • Duration
A landslide could cause a ______ wave • Tide • Progressive • Tsunami
Wave Motion Wave Motion
Wave Motion • Wind-generated waves are progressive waves because they travel across the sea surface. There are two basic motions associated with an ocean wave: • the forward movement of the wave form • the orbital motion of water particles beneath the wave • It is the wave energy not water molecules themselves that moves across the sea surface.
Wave Motion Forward Movement The motion of water particles beneath waves. Orbital movement
Pipeline-North Shore Hawaii
Wave Motion • In deep water most waves do not interact with the sea bottom and are calleddeep-water waves. The orbits of the water molecules are circular.
Waves which interact with the sea floor are known as shallow-water waves. The orbits of the water molecules become elliptical – friction, slow. (Shallow-water waves can occur in the deep ocean if the wavelength is long enough.)
WAVE DEPTH • Wave depth is one half of the wavelength. • If the wavelength is 20 meters the depth is 10m
Life History of Ocean Wavesgetting closer to the shore….. • In shallow water the sea bottomtransforms the wave’s properties. • Bottom friction alters both • Wave form • Speed (Celerity)
The two types of motion found in waves are • Forward and Backward • Orbital and Downward • Forward and Downward • Forward and Orbital
Waves that interact with the ocean floor are called • Shallow water waves • Deep water waves • Orbital waves • Fetch
Waves that do not interact with the ocean floor are called • Deep water waves • Shallow water waves • Orbital waves • Fetch
As waves enter shallow water • Wavelength shortens • Height increases • Speed decreases PERIOD REMAINS THE SAME What is the one factor that determines the wave speed of shallow water waves? DEPTH
Notice how waves bunch together as they approach shore. This is because the waves in shallower water travel slower than the waves behind in deeper water. Speed Decreases Wavelength Decreases FRICTION Height increases
Deep/Shallow Waves Depth = 1/20th wavelength Top of wave moves faster than the bottom of the wave and the wave breaks The wave comes into contact with the bottom and slows down the wave. Wave height increases Ocean bottom does not affect the wave
As a wave moves to shore • Speed increases • Speed decreases • Speed remains the same
As a wave moves to shore • Height increases • Height decreases • Height remains the same
As a wave moves to shore • Period increases • Period decreases • Period remains the same
Waves ultimately break when the top of the wave gets ahead of the bottom of the wave due to more friction at the bottom.The depth is usually 1.3 times the wave height = 1/7th of the wavelength Breaking Waves
The type of breaker formed is determined by the steepness of the surf zone. Spilling breaker – wide, flat Plunging breaker – narrow, steep Surging breaker – V. narrow, V. steep
Waves may not break, but instead can be reflected off near vertical surfaces producing outgoing waves.
Wave refractionrefers to the bending of the wave crest as waves enter shallow water. It is due to differences in speed produced by differences in water depth. Shallower area
Summary • Waves are disturbances that move along or beneath the sea surface. • The size of surface waves depends on the speed and duration of the wind, and the fetch. • Waves affect water to a depth equal to or less than one-half their wavelength.
