Oceanography Quiz #2

What Causes Waves

All waves being as disturbances; from a disturbing force.

Evolution of a wave as it approaches the shore

As deep-water waves of swell move toward continental margins over gradually shoaling water, they eventually encounter water depths that are less than one-half of their wavelength and become transitional waves. It starts scraping the bottom and becomes a shallow-water wave and slows down. The shoaling depth interfere with water particle movements at the base of the wave, so the wave speed decreases. As one wave slows, the following waveform, which is still moving at its original speed, moves closer to the wave that is being slowed, causing a decrease in wavelength. The wave energy that remains must go somewhere, so wave height increases. This increase in wave height combined with the decrease in wavelength causes an increase in wave steepness. When the wave steepness reaches the 1:7 ration, the waves break as surf. When breaking they curl forward because of momentum and topple forward. Breakers - waves that breaks, depend on the topography of the ocean floor. Spilling breakers - just spill over. Where the energy is released over a long period because of the gentle slopping. Plunging breaker - occurs from a steeping sloping ocean floor. Occurs at an active continental margin. Curls over in a tube. Best for surfing. Plunging breaker - occurs from an abrupt slope. Suddenly encounters the ocean-floor and waves come out of nowhere. Sometimes occur in the middle of the ocean if there is an undersea mountain the wave base will hit the top and create waves.

Short Answer: As wave move into shallow water, the wave crests tend to become parallel to the shoreline. Why does this occur?

As waves move into shallow water and approach a straight shoreline they are refracted. Refraction is the bending of each wave crest as waves approach the shore; they conform to the slope of the coastline. Thus, as they approach a shoreline they tend to align themselves parallel to the shore. The refraction of waves along an irregular shoreline distributes wave energy unevenly along the shore.

Basic Characteristic of waves

Crest = Succession of high parts of the waves. That alternate with... Trough = the low parts of the wave. wave height = Marked with the symbol H. It is the vertical distance between a crest and a trough. wave length = Marked with an L. The distance from crest to crest or trough to trough. still water level = the level of the water if there were no waves. Halfway between the crests and the troughs.

Short Answer: Define deepwater-wave and shallow water-wave and highlight the differences.

Deepwater waves are waves with a depth that is greater than the wave base (L/2). They have no interference with the ocean bottom. They include all wind-generated waves in the open ocean. The speed of deep-water waves are dependent upon wavelength, because it carries more energy. It is calculated as s=1.25 (Square Root) L The longer the wavelength, the faster the wave travels. Conversely, Shallowater waves are wave in which depth is less and 1/20 of the wavelength. Shallowater water waves scrap/touch the bottom of floor. The speed is severely restricted by the friction. The shallower the water means the greater friction and the slower the wave. The shallower the water means the greater friction and the slower the wave.

Mixed interference

In real live we see a combination of constructive and destructive interferences, caused by multiple disturbing forces. It is likely that two or more swells of different heights and lengths will come together and produce a mixture of the two interference. This explains the varied sequence of higher and lower waves called surf beat.

Constructive and destructive interference

Interference is when swells from different storms run together. More theoretical Constructive = occurs when wave trains having the same wavelength come together in phase (meaning crest to crest and trough to trough) If the displacement from each wave are added together, the interference pattern results in a wave with the same wavelength as the two overlapping wave systems but with a wave height equal to the sum of the individual waves Destructive = occurs when wave trains having the same wavelength come together out of phase (crest from one wave coincides with the trough from a second wave) If the waves have identical heights, the sum of the crest and the trough of another is zero, so the energies of the two waves cancel each other.

Short Answer: List and explain the factors that determine to what size wind-generated waves can grow and explain why they are important.

Size is determined by the magnitude of the disturbing force. The first factor is windspeed. The process of wind-generated waves, it takes time for the earth to transmit energy to the surface. Thus bodies of water such as Lake Michigan cannot get very big waves because there is not enough time to grow big. Another factor is fetch, which is the lengths of winds trajectory over the ware. Duration, determines the time the wind is blowing.

Derived characteristics of a wave

Steepness = the ratio of wave height to wave length - H/L Period = The time it takes one full wave - one wavelength to pass a fixed position. Frequency = the number of wave crests passing a fixed location per unit of time and is the inverse of the period 1/period(t). Speed = the rate at which a wave travels. It is the distance traveled divided by the travel time. Wave length L/Period(T)

Wave Base

The point at which the circular orbits become so small that movement is negligible. It is equal to one-half the wavelength (L/2). The longer the wave, the deeper the wave base.

Definition of Waves

They are moving energy. Moving energy traveling along an interface between fluids and different densities (in this case water and air). Waves transmit the energy imparted by the disturbing force.

How water waves transmit energy

They transmit the energy imparted by the disturbing force. The water itself does not actually move in the direction of the energy passing through it. The particles in water move in a circle and transmit energy from one particle to another. Throught orbitalwaves - involve longitudinal and transverse waves, move in a circular orbit. They transmit energy along interface between two fluids of different density.

Short Answer: What is an ocean wave & what causes it.

Waves are moving energy. Waves are moving energy traveling along an interface between fluids and different densities. For ocean waves they move along an air-water interface across the ocean surface. Waves are caused by a disturbing force. Such as wind blowing along the surface or a rock splashing in the water. These disturbances are the energy that cause ocean waves to form. Waves transmit the energy imparted by the disturbing force.

Limitations of the growth of waves:

When the waves speed equals the wind speed, neither wave height nor wavelength can change (or grow) because there is no net energy exchange and the wave has reached its maximum size.

Tsunamis

a large destructive wave that occasionally roll into harbors. It is caused by the vertical displacement on the ocean-floor (ie Earthquake). Occur at convergent plate-boundaries. Occur in the Pacific ocean more than anywhere else. It originates in the subduction zone, radiates as concentric rings that emanate outward. Speed is 400 m/p. Wavelength is 120 miles. Wave Height 1.6 ft. THey are almost undetectable on the ocean surface. The disturbing force is on the ocean floor, thus wave-base is lower than ocean floor. They are more destructive than wind-generated waves because of the amount of energy caused by the disturbing force. Vertical displacement changes the volume of the ocean basin, which affects the entire water column.

gravity waves

bigger than .7 inches. Gravity becomes the restoring force. Before waves catch any wind, wind and water run parallel to each other and create friction. This creates eddies and the disturbance roughs up the surface. When the waves develop the height, wavelength, and speed grow. Height increases more rapidly than wavelength. When the steepness exceeds 1/7 it breaks due to the strength of gravity.

Speed of deep-water waves

deep-water wave = if the water depth is greater than the wave base. The speed is dependent upon the wavelength. Speed(in meters) = 1.25 (squareroot) L. The longer the longer the wavelength, the faster the wave travels.

rogue waves"

massive, solitary spontaneous ocean waves that can reach enormous height and often occur at times when normal ocean waves are not unusually large. They are caused by constructive wave interference where multiple waves overlap in-phase to produce an extremely large wave.

Speed of shallow water-waves:

shallow-water waves is less than 1/20 of the wavelength, they touch the ocean floor, thus it interferes with the waves orbital motion. It is influenced only by gravitational acceleration and water depth. The deeper the water, the faster the wave travels.

The characteristic of the sea surface in the "sea area"

the area where wind driven waves are generated. Characterized by choppiness and waves moving in many directions. The waves have a variety of periods and wavelengths (most of them short) due to frequently changing wind speed and direction. When waves leave the area they are generated - they are more triangular when they occur in the areas they were created in. Swell = waves outside the place they are created (outside the sea area).

The relationship between wave size...and fetch

the distance over which the wind blows in one direction.

The relationship between wave size...and duration

the length of time during which the wind blows in one direction

Wave dispersion beyond the "sea area"

the sorting our process of wave length. If created locally they are not always well-sorted, ie chopping sea. Beyond the sea-are uniform waves. the sorting of waves by their wavelength. Waves with longer wavelengths travel faster and thus leave the sea area first. They are followed by slower, shorter wave trains, or groups of waves. Waves of many wavelengths are present in the generating reas. Wave speed depends on wavelength in deep water, however, so the longer waves "out run" the shorter ones.

The relationship between wave size...and wind speed

there are conditions wind speed (fetch and duration) that are necessary to produce a fully developed sea. For a given wind speed, there is a minimum fetch and duration of wind beyond which the waves cannot grow. Waves cannot grow because of an equilibrium condition, called a fully developed sea, has been achieved. Waves can grow no further in a fully developed sea because they lose as much energy breaking whitecaps under the force of gravity as they receive from wind.

Wave refraction and its consequences

wave refraction is the bending of each wave crest as waves approach the shore. Waves bend. As they come toward the coastline the wave crests conform to the slope of the coastline. Waves bend then slow down and scrape the bottom. Waves come in parallel to the beach.

Capillary waves

wind generated- waves that begin as ripples, where the wavelength is less than .7 inches. The main restoring force is the capillary force: the surface tension is trying to pull the ocean surface flat again, once the ripples develop they catch more wind and get bigger. The water "catches" more of the wind, allowing the wind and ocean surface to interact more efficiently. V-shaped.