Internal waves are fascinating phenomena that occur within a body of water, rather than on its surface.
What Are Internal Waves?
Unlike the familiar waves seen crashing on a beach, internal waves travel along the boundaries between layers of water with different densities. This difference in density is often caused by variations in temperature or salinity. Think of them as ripples or undulations happening deep beneath the surface, sometimes hundreds or even thousands of feet down.
Because the density differences are typically much smaller than the difference between water and air (which drives surface waves), internal waves can be much larger in amplitude and slower-moving than surface waves. They can sometimes be visible from space under certain conditions or detected by specialized oceanographic equipment.
How Do Internal Waves Form?
Internal waves are generated when water moving in a layer meets an obstacle, like a ridge. This interaction causes a disturbance at the interface between the water layers, creating a wave that propagates internally.
Here are some common ways internal waves can form:
- Interaction with Topography: As mentioned in the reference, when currents flow over underwater features such as:
- Seamounts
- Ridges
- Canyons (like the submarine canyon in Monterey Bay, which contributes to its complex internal wave field)
The uplift or downwelling of water caused by the obstacle can trigger internal waves.
- Tidal Flow: Tidal currents moving over varying seafloor topography are a major global source of internal waves.
- Wind Stress: Strong winds or storms can create turbulent mixing near the surface, which can propagate downwards and generate internal waves.
- Density Fronts: When bodies of water with different densities collide or interact, the interface between them can become unstable, generating waves.
The process often involves the displacement of water parcels across the density interface. Gravity tries to restore the water parcels to their equilibrium level, causing oscillations that propagate as waves. These waves carry significant amounts of energy across the ocean basins and play a crucial role in mixing ocean waters.
For example, due to the submarine canyon, Monterey Bay has a complex internal wave field. This is a direct result of how the Bay's unique underwater geography interacts with moving water layers, constantly generating and shaping internal waves.
