Ocean waves     Waverider Buoys     Tsunami waves     Tide wave     Tidal bores     Planetary waves

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Most ocean waves are seen as a disturbance of the water surface.

Water in the upper layers of the oceans is in constant motion, produced primarily by the action of winds blowing across the surface. The effect of the interaction between winds and the sea surface results in waves and currents.

Ocean waves vary in size from ripples at the millimetre scale to storm waves as high as 30 metres.

Waves around the Australian coastline are measured by Wave rider (Waverider is the manufactures name) buoys. Each Wave rider buoy is anchored to the sea floor. The buoys are specially designed to follow the movement of the ocean surface.

The anchoring system includes a length of rubber chord that is capable of stretching up to three times its length.

This flexibility of the mooring allows the Wave rider to more truly follow the fluctuating ocean surface.

Fluctuations in the ocean surface are measured by either an accelerometer mounted inside the Wave rider buoy or a GPS unit and converted to radio signals that are transmitted to a receiver station on shore.

The electronics and the navigation light are powered for up to twelve months by a bank of dry cell batteries mounted around the inside of the hull.

Tsunamis are long-wavelength shock waves generated by sudden changes in sea floor in coastal areas. This occurs as the result of earthquakes, landslides as landslides into the ocean or submarine slumps and volcanic eruptions.

A tsunami is a series of ocean waves that sends surges of water, sometimes reaching heights of over 30 meters, onto land. These walls of water can cause widespread destruction when they crash ashore. These awe-inspiring waves are typically caused by large, undersea earthquakes at tectonic plate boundaries. When the ocean floor at a plate boundary rises or falls suddenly it displaces the water above it and launches the rolling waves that will become a tsunami. 

Tsunami's have very long wave lengths, in the order of hundreds of kilometres in length. In the Pacific ocean, where the depth is around 4300 m a tsunami can travel at 800 km/h, a phenomenal speed, almost as fast as the cruising speed of a jumbo jet (893 km/h). 

A tsunami’s trough, the low point beneath the wave’s crest, often reaches shore first. When it does, it produces a vacuum effect that sucks coastal water seaward and exposes harbor and sea floors. This retreating of sea water is an important warning sign of a tsunami, because the wave’s crest and its enormous volume of water typically hit shore five minutes or so later.

Read about Meteorological Tsunami

Tides are a very long-period wave that moves through the oceans in response to the gravitational forces exerted by the moon and sun. Tides originate in the oceans and progress toward the coastlines where they appear as the regular rise and fall of the sea surface.

When the highest part, or crest of the wave reaches a particular location, high tide occurs.  

When the lowest part of the wave or its trough reaches the coast, low tide occurs.

Although tsunamis have been referred to as "Tidal waves" in the past. Tide waves are in no way related to tsunamis. Tide waves have an entirely different origin to tsunami and are truly everyday events, whereas tsunamis are relatively rare events.

The interaction of the leading edge of the incoming tide with the outgoing current from a river can sometimes produce a solitary wave that proceeds up the river from its mouth. 

Bores occur in relatively few locations worldwide, usually in areas with a large tidal range between high and low water and where incoming tides are funneled into a shallow, narrowing river or lake via a broad bay.

A tidal bore is a surge of water propagating upstream as the tidal flow turns to rising and the flood tide rushes into a funnel shaped river mouth with shallow waters. The bore forms during the spring tides when the tidal range exceeds 4 to 6 m and the estuary bathymetry amplifies the tidal range with a low freshwater level.

It is estimated worldwide that over 400 estuaries are affected by a tidal bore, on all continents but Antarctica. A bore is a discontinuity of the water depth and it represents a hydrodynamic shock.

Planetary waves cross the oceans along parallels and interact with general oceanic circulation.

These are either Rossby waves, which go from East to West or Kelvin waves which move in the opposite direction.  They may be reflected off the continents and return in the opposite direction, or follow coastlines.  These waves and their reflections play a key role in the El Niño phenomenon.

There are two types of Kelvin waves, coastal and equatorial, they are both gravity driven and non-dispersive.

Reference:

Tidal Bore information and images modified from: Chanson H., 2009. environmental, ecological and cultural impacts of tidal bores. IWEH. International Workshop on Environmental Hydraulics Theoretical, Experimental and Computational Solutions, Valencia, 2009.

Waverider buoy information from: www.qld.gov.au/waves. Glossary and About wave monitoring.