Tides are a complicated phenomenon.
Tides in the ocean are generated by the moon's gravitational
pull, and they affect more than just how much room on the beach
there is for a chair and umbrella. They're actually long
period waves that move through the oceans in response to forces
exerted by the moon and sun, making their way towards the
coastlines, where they appear as the regular rise and fall of the
sea surface.
And they may also help to slow down the rate of global warming
of the atmosphere, partially by forming a complex system of
underwater waves that can help move heat into the ocean
interior. That complex system of waves is essentially a different
type of tide, called Internal Tides.
NASA can see how Internal Tides move and flow in the ocean here.
Across a long swath of the North Pacific Ocean sits the Hawaiian
Ridge, a massive underwater structure high enough in a few
places to reach the ocean surface and form the islands of
our 50th state. The tidal currents that are generated by
the moon's gravitation impact the Hawaiian Ridge, causing deep
dense water to be forced upward. Gravity and buoyancy forces then
tug the water down and up again, creating oscillations. Those
oscillations are internal waves. But since the waves oscillate at
the tidal period, which is the time it takes for tides to
complete one cycle, from high to low, and back to high again in
roughly 12 hours, we call them Internal Tides.
Once generated along the ridge, these internal tides move away
from it, both northwards and southwards, and can sometimes go
as far as thousands of miles. underneath the surface, the
waves can be as big as hundreds of feet. But on the ocean
surface, they're often only a few inches high, barely large
enough to notice.
Yet instruments on satellites, like altimeters, are capable of
measuring those small surface waves, and NASA can predict
Internal Tides based on years of compiled satellite data.
The ocean is filled with underwater topography, from
mountains to ridges to trenches, creating many sources of
Internal Tides all over the global ocean and giving rise to
the many complicated patterns seen in this visualization.
Although Internal Tides might seem insignificant, being only a
few inches on the ocean surface, they provide oceanographers with
a unique way to map and study the much larger internal water
motion. That water motion and subsequent mixing between warm
shallow water and cold deeper water is thought to move heat
from global warming of Earth's atmosphere down into the ocean interior.
In other words, Internal Tides are an incredibly significant
mechanism and have a sizable impact on the Earth's climate.