Waves + Water Dynamics

• Due to Ekman Transport, the upper 100m of the surface ocean moves approx. 90º to the (right / left) in the northern hemisphere and to the (right / left) in the southern
• At the Equator winds converge which causes (upwelling / downwelling) of water
• If wind blows south along the eastern coast of North America, coastal waters will undergo downwelling
• ENSO stands for El Niño Southern Oscillations. It includes Warm and Cool phases (La Niña and El Niño)
• Conveyer-Belt Circulation is an integrated model combining surface currents and deep thermohaline circulation. Changes in the global deep-water circulation pattern can dramatically and abruptly affect climate. It takes 1000 years
• All waves begin as disturbances. The energy that causes waves to form is called a disturbing force
• Internal Waves are associated with pycnocline, larger than surface waves, caused by various factors, and can be a possible hazard for submarines
• Mass movement into the ocean and shifts in the ocean floor can generate waves. Tides are due to the gravitational pull of the moon. Human causes include boats causing a wake
• Waves transmit energy through cyclic motion of particles in the ocean. The water does not travel in the direction of the wave
• Progressive waves oscillate uniformly and progress without breaking
• Longitudinal waves compress and decompress as they travel
• Transverse waves transmit energy at right angles to the direction of moving particles and generally only transmit through solids
• Orbital waves on the ocean surface are a combination of longitudinal and transverse waves
• Wave characteristics include crest, trough, wave height, and wave length
• Wave steepness, wave period, wave frequency, and wave speed are important orbital wave characteristics
• The diameter of orbital motion decreases with the depth of water. Wave base is where there is hardly any motion due to wave activity
• Number of wave crests passing a fixed location per unit time

  Equal to the inverse of period or 1/T
• Wave speed

  Wavelength (L) divided by period (T)
• Orbital Wave Characteristics

  • Diameter of orbital motion decreases with depth of water
  • Wave base = ½ L
  • Hardly any motion below wave base due to wave activity
• Water molecules transmit the wave energy but move in a circle and end up roughly where they started
• Circular orbits of an object floating on the surface have a diameter equal to the wave height
• Deep Water Waves


  • Wave base = depth where orbital movement of water particles stops
  • All wind-generated waves in open ocean are deep water waves
  • Speed of deep water wave is function on wavelength
  • The longer the wavelength, the faster the wave travels
• Shallow water waves


  • Water depth (z) is less than 1/20 L
  • Water feels seafloor so it interferes with the circular orbital motion, causing orbits to become progressively flattened
  • Speed is a function of depth: The deeper the water, the faster the wave travels
• Transitional Waves

  • Characteristics of both deep- and shallow-water waves
  • Depth is greater than 1/20 wavelength, but less than ½ wavelength
• Wind Generated Waves

  • Life history of a wind generated wave includes: Origin in a windy region of the ocean
  • Movement across great expanses of open water without subsequent aid of wind
  • Termination when it breaks and releases energy, either in the open ocean or against the shore
  • Factors affecting wave energy: Wind speed
  • Wind duration – length of time during which the wind blows in one direction
  • Fetch – distance over which wind blows
  • Wave heights usually less than 2 meters (6.6 feet)
  • Breakers called whitecaps form when wave reaches critical steepness
• Interference Patterns

  • Collision of two or more wave systems, interfering with one another
  • Constructive interference: In-phase waves with about the same wavelengths
  • Destructive interference: Out-of-phase waves with about the same wavelengths
  • Mixed interference: Two wave groups with different wavelengths and different wave heights
• Surf zone - zone of breaking waves near shore
• Shoaling


  Water becoming gradually more shallow
• When deep water waves encounter shoaling water less than ½ their wavelength


  They become transitional waves
• As a deep-water wave becomes a shallow-water wave

  1. Wave speed decreases

  2. Wavelength decreases

  3. Wave height increases

  4. Wave steepness (height/wavelength) increases

  5. When steepness > 1/7, wave breaks
• Breakers - Waves break close to shore
• Wave Refraction - Waves bend as they approach shore
• Wave Reflection - Waves and wave energy bounced back from barrier
• Rip Currents - Water finds a corridor to move back out into the ocean
• Tsunamis originate from sudden sea floor topography changes
• Causes of tsunamis

  • Earthquakes
  • Underwater landslides
  • Underwater volcano collapse
  • Underwater volcanic eruption
  • Meteorite impact
• Tsunamis have long wavelengths (> 200 km or 125 miles)
• Tsunamis encompass entire water column, regardless of ocean depth
• Tsunamis can pass undetected under boats in open ocean
• Sea level can rise up to 40 meters (131 feet) when a tsunami reaches shore