interannual waves in ocean and atmosphere

Question 1

what are the two distinct types of waves?

Answer 1

• Electromagnetic waves that consist of varying electric and magnetic fields the can move through a vacuum
  
  • Mechanical waves that require a medium for the transmission

Question 2

what is a wave?

Answer 2

Can think of a wave as a method of transferring energy from one place to another, without transferring matter. This is a very important concept in the earths behaviour. Waves of different types and of different scales.

Question 3

what are transverse waves?

Answer 3

• Transverse waves- those with particles oscillating at right angles to the direction of their advance. Examples of these are water waves, seismic S waves and light waves. Important characteristics of transverse waves is a disturbance at A causes a disturbance of a particle that drags its neighbours along with it until point B. If the disturbance at the source continues, the wave is maintained, and if it is a simple harmonic, then a plot of the displacement of the particles at a single point is a sine curve.

Question 4

what are longitudina waves?

Answer 4

• Longitudinal waves- those with points vibrating in the same direction as the advance. Sound waves and seismic P waves are examples of these.

Question 5

what are progressive waves?

Answer 5

• Progressive waves- nomenclature- standard terms used to describe waves.

Question 6

what is a wave period?

Answer 6

• Wave period (T) is the time of the wave to move a distance equal to one wavelength

Question 7

what is wave frequency?

Answer 7

• Wave frequency (f) is the number of wave crests that pass a point on the ocean surface in a given time

Question 8

what is the equation for wave period and frequency?

Answer 8

• Wave period and wave frequency are related by a simple equation T= 1/f.

Question 9

what is celerity?

Answer 9

• Wave speed is called “celerity”, because there is essentially no net forward movement of the water as the wave passes. It is calculated as c= NT or c = f x λ .

Question 10

what is phase velocity?

Answer 10

• This is the speed of a wave crest, and is also known as the phase velocity:: only the wave energy and waveform, and not the water, move forward with the wave. In deep water, the water molecules within waves move in circular orbital paths and only energy, not water, is transported forward.

Question 11

what are the two concepts of phase velocity?

Answer 11

• Two concepts:
  
  • The phase velocity of celerity: for any given phase of the wave. Eg, the crest will appear to travel at the phase velocity
  • The group velocity: the speed of the envelope of a packet of waves or “wave train”

Question 12

what does the vertical line mean in phase velocity?

Answer 12

• The vertical line marks a crest and shows the phase velocity. It progresses through the envelope showing that in this case, the phase velocity is greater than the group velocity.

Question 13

what is wave speed?

Answer 13

phase velocity and group velocity. Wave waves usually travel in wave groups or wave trains. Velocity of individual crest (phase velocity) shows one bump on the wave. These can be seen when a boat moves. A ship bow an stern waves (wake) travel out from the ship as wave trains.

Question 14

what does wave motion require?

Answer 14

• Wave motion requires both a force to disturb the flat water surface and a restoring forces that tends to bring the surface back to level.

Question 15

what is surface tension?

Answer 15

• Surface tension and gravity are the principal restoring forces acting on ocean waves.
  
  • Surface tension: pulls the surface equally in all directions, contracting the surface to its minimum area- a flat plane.

Question 16

what is gravitys role on restoring forces?

Answer 16

Gravity acts on the water molecules within a wave and causes a pressure gradient to develop beneath the sloping surface. The water flows in response to the pressure gradients and tend to flatten the sea surface

Question 17

what are the forces that create waves?

Answer 17

Waves must be formed initially by a displacing force. Most ocean waves are caused by interaction of winds with the water surface

Question 18

how are waves also created?

Answer 18

• Impacts on ocean water
  
  • Rapid displacement of ocean water
  • Gravitational attraction between the earth, moon and sun
  • By the passage of vessels or marine animals through the sea surface, what is called the “wake”.

Question 19

how does wind create waves?

Answer 19

• Forces that creates waves- role of wind. Wind induces a surface current, around 3% of the wind speed at the very surface. Wind is also the main generator of ocean surface waves

Question 20

what are capillary waves?

Answer 20

• Light winds blowing over a flat smooth sea surface first create capillary waves. Capillary waves have a maximum wavelength of 1.73 m. Capillary waves disappear quickly if the wind stops as they are restored by surface tension.

Question 21

what happens if wind builds up and increases?

Answer 21

• If the wind continues and increase, waves are built up progressively, to longer wavelengths and greater heights.

Question 22

what is a shear stress?

Answer 22

• Wind blowing across a flat sea surface create tiny areas of elevated or depressed sea surface. A shear stress develops between air and water, because of the velocity difference across the air-sea interface.

Question 23

how do waves build with energy?

Answer 23

• Winds lift leeward side of the wave and push on the windward side, imparting more energy so the waves build.

Question 24

how does wind energy get absorbed by waves?

Answer 24

• As wind energy is absorbed by waves, their height, speed, period and wavelength are increased. As the waves height builds by the winds, its shape is modified from that of capillary waves. The shape firest becomes close to the smooth sine wave form. Wave shape eventually becomes trochoidal

Question 25

what does calm mean in nautical terms?

Answer 25

• Calm: there are no significant waves and the sea surface is flat

Question 26

what does sea mean in nautical terms?

Answer 26

• Sea: winds never blow uniformly over water so waves of many different wavelengths and heights are created by a storm

Question 27

what does swell mean in nautical terms?

Answer 27

• Swell: in many areas where winds are light or the air still. The sea surface still has waves but these are generally smooth and same wavelength.

Question 28

what does whitecap mean in nautical terms?

Answer 28

• Whitecaps: breaking waves.

Question 29

why do waves break?

Answer 29

• Waves break because they have become too steep, when the steepness of a deep-water wave reaches 1:7- wave height equals one sevenths of wavelength, the wave becomes unstable and the crest tumbles sown the forward slope of the wave creating a breaking wave.

Question 30

what is the max height of waves?

Answer 30

• Max height of waves created by any specific storm or series of storms depends on the wind speed and the length of time the wind lows.
  
  • The maximum height also depends on the fetch: the distance over which the winds blow across the waters to crease waves.

Question 31

how can fetch be limited?

Answer 31

• Fetch can be limited by:
The presence of a coastline,
Where the storm is completely over water by the dimensions of the storm itself.
• For a given wind speed, max possible wave heights increase as the fetch increases.
• Max wave heights only reached if the wind blows for long enough.

Question 32

how can the sea surface appear to alternate between periods of low and high waves?

Answer 32

• When wave trains of similar wave heights but slightly different periods arrive at the same time, the sea surface will appear to alternate between periods of low and high waves.

Question 33

what is wave interference?

Answer 33

• The process of wave addition and subtraction, called wave interference, is what causes waves to vary in height in irregular patterns.

Question 34

what is waveform?

Answer 34

• When 2 set of waves of very similar wavelengths arrive at the same location at the same time, their addition can produce a long period of variations of the wave height in the resulting waveform.

Question 35

how can a chaotic sea and dangerous conditions be formed?

Answer 35

• It is possible to get a cross-swell resulting from two wave systems generating by wind patterns of 90 degrees angles. This can set up a chaotic sea and dangerous conditions.

Question 36

how do waves from different periods becomes separated?

what is wave dispersion?

Answer 36

• Wave trains of different periods becomes separated as they move away from the storm centre, where they were created because the wave speed increased with increasing wavelength.

Question 37

why do longer wavelengths travel faster and what does this cause?

Answer 37

Longer wavelength waves travel faster and so move out ahead of the shorter wavelength waves. As the waves become separated by wavelength, the sea becomes a swell- smooth undulations without sharp or breaking crests.

Question 38

why do waves approach the shoreline at an angle?

what is wave refraction?

Answer 38

• Waves usually approach a shoreline at an angle.
  
  • Because one end of the wave crest line enters shallow water and slows while the rest of the wave is still deeper water and travelling at its original speed, the wave refracted, or bent.

Question 39

why does wave refraction concentrate wave energy on headlands?

Answer 39

• Wave refraction tends to concentrate wave energy on headlands and spread it out in bays.

Question 40

what is wave diffraction?

Answer 40

• Waves are diffracted when part of the wave is blocked by a solid object. Breakwaters do not protect the are behind them entirely from waves, as the waves spread out behind the breakwater as they diffract.

Question 41

how do waves break?

Answer 41

when waves enter shallow water, and interact with the seafloor, their height is reduced slowly as the water depth decreases. In water depths of L/10 and less, the trend reverses and the wave height increases rapidly as water depth decreases. This is why tsunami waves steepen, due to the wave depth as fraction of wavelength increasing.

Question 42

how do waves break in shallow water?

Answer 42

waves steepness increases until the wave becomes unstable and breaks. The area off shore within which waves are breaking is called the surf zone.
There is spilling breaker, plunging breaker, collapsing breaker and surging breaker.

Question 43

how do internal waves occur in shallow water?

Answer 43

waves also occur on density interfaces within the ocean, mainly on the thermocline or pycnocline. Commonly visible from surface due to convergences and divergences. Commonly visible from space due to affects on sea surface. Breaking internal waves may be important for mixing.

Question 44

what are characteristics of water surface waves?

Answer 44

• Speed terms
  
  • Reflection
  • Refraction
  • Diffraction
  • Dispersion
  • Breaking

Question 45

what are the origins of Rossby waves?

Answer 45

• Origins: rossby waves originate from fluid shear generated by the Coriolis effect in a rotating planetary body.

Question 46

what are the occurences of Rossby waves?

Answer 46

• Occurrence: rossby waves occur in the atmosphere and in the ocean on different temporal and length scales

Question 47

what are rossby waves like in the atmosphere?

Answer 47

• In the atmosphere: rossby waves shape major patterns of weather especially in winter

Question 48

what are rossby waves like in the ocean?

Answer 48

• In the ocean: rossby waves interact with major current circulation and play a key role in transmitting climatic events especially in the low latitudes.

Question 49

how do rossby waves form?

Answer 49

redistribute momentum, set adjust time to large scale forcing, transmit energy, intensify W boundary currents. Delay effects of climatic events, and interact with general circulation.

Question 50

what are the origins of Kelvin waves?

Answer 50

• Origins: combination of gravity wave and Coriolis forcing that also depends on the existence of a wave guide at either vertical boundaries or the equator.

Question 51

what are the occurences of Kelvin waves?

Answer 51

• Occurrence: vertical boundaries, or at the equator. (oceanic-coasts, or atmospheric-mountain ranges). At the equator propagate only eastwards.

Question 52

what are kelvin waves like in the atmosphere?

Answer 52

• In the atmosphere: plays a key role in the adjustment of the tropical atmosphere to convective heating.

Question 53

what are kelvin waves like in the ocean?

Answer 53

• The ocean: plays a key role in tides, in the adjustment of the tropical ocean to wind forcing.

Question 54

what are oceanic kelvin waves?

Answer 54

• Oceanic kelvin waves: hybrid forcing- gravity wave and coriolis effect.

Question 55

what are coastal kelvin waves?

Answer 55

• Coastal kelvin waves: only propagate in one direction. Earths rotation acts to pile up fluid against boundary. Offshore pressure gradient force must balance coriolis force.

Question 56

what are atmospheric kelvin waves?

Answer 56

• Atmospheric kelvin waves: occur in troposphere and stratosphere.

Question 57

what is the equatorial pacific ocean circulation?

Answer 57

• Equatorial pacific ocean circulation: no coriolis effect at the equator. Complicated, because southern hemisphere trade winds extend over equator.

Question 58

what is El Nino?

Answer 58

• El Nino: periodic warming of eastern pacific. Associated with the reduction in air pressure.