Ocean Waves

Marine Science - Waves

What is an ocean wave?

A disturbance caused by energy moving through water. The energy travels forward, but water particles mainly move in circular orbits rather than traveling forward with the wave.

What is an orbital wave?

A wave in which water particles move in closed circular paths ( orbits) as the wave passes. Orbital waves are a type of progressive wave because the wave form moves forward.

What are the main parts of a wave?

1. Crest: highest point above average water level.

2. Trough: lowest point below average water level.

3. Wave height: vertical distance from crest to adjacent trough.

4. Wavelength: horizontal distance between successive crests or troughs.

What are wave periods and wave frequency?

1. Wave period: time required for a wave to travel one wavelength.

2. Wave frequency: number of waves passing a fixed point per second.

How does wave motion change with depth?

Water particles move in smaller circular orbits as depth increases. Wave motion becomes negligible below about ½ the wavelength, where orbit diameter is only about 1/23 of the surface diameter.

What causes larger progressive waves?

Wind commonly produces ocean waves, while atmospheric pressure changes and the gravitational effects of the Sun and Moon can produce much larger waves, including flooding surges and tides.

How do water particles move within a wave?

Particles move in coordinated circular orbits. At the crest, particles move in the same directions as the wave; at the trough, they move in the opposite direction.

What is Stokes drift?

The net forward movement of water caused because particles in the upper part of their circular orbits move farther forward that particles in the lower part move backward.

How are ocean waves classified?

By their disturbing force, how long that force continues, the restoring force that flattens them, and their wavelength. Wave height is usually bot used because it varies with water depth and other factors.

What is a free wave?

A wave the continues to move after the force that created it stops. Examples include wind waves moving away from a storm and tsunamis.

What is a forced wave?

A wave that is continually maintained by the force that created it. Tides are forced waves maintained by the gravitational pull of the Moon and Sun.

What is a restoring force?

The force that returns a disturbed water surface toward flatness aftr a wave forms.

Why do waves continue after forming?

The restoring force overcompensates, causing the water to oscillate back and fourth instead of immediately becoming flat.

What is the restoring force for waves shorter that 1.73 cm?

Cohesion - the attraction between water molecules caused by hydrogen bonds.

What is the restoring force for waves longer than 1.73 cm?

Gravity is the main restoring force. These waves are called gravity waves.

Why can gravity waves travel thousands of miles?

Their circular water motion is nearly friction-free, allowing them to travel long distances without losing much energy.

How is ocean wave energy distributed by wave period?

Most energy is concentrated in wind waves. Tsunamis have longer periods and can briefly carry enormous amounts of energy, while tides have very long periods of 12 or 24 hours.