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How the Coriolis effect influences ocean swells and waves

Swell: waves are not mass | Photo: Shutterstock

The Coriolis effect occurs when the Earth's rotation causes moving things - such as winds and ocean currents - to curve instead of moving in a straight line.

Does it sound strange? Here's a visual example using the spinning carousel.

Imagine you're sitting on a merry-go-round (carousel) spinning counterclockwise.

Now, you try to roll a ball straight across to a friend sitting across from you. What happens?

To you (on the spinning carousel), the ball curves to the right instead of going straight.

But if someone were watching from above (not on the carousel), they would see that the ball actually moved in a straight line, but the carousel moved underneath it.

How This Relates to Earth

The Earth spins like a giant merry-go-round we've seen above, from west to east, at around 1,000 miles per hour (1,600 kilometers per hour) at the equator. 

Thanks to the Coriolis force, objects moving long distances, like winds and ocean currents, appear to curve instead of going straight.

In the Northern Hemisphere, moving objects curve to the right; in the Southern Hemisphere, they curve to the left.

If you had to draw the curving lines over the planet, it would have an S-shaped form.

This is also how hurricanes and typhoons spin due to this effect: counterclockwise in the Northern Hemisphere (top half of the "S") and clockwise in the Southern Hemisphere (bottom half of the "S").

Coriolis effect: the force is more pronounced in the equator

Applying the Coriolis Effect to Ocean Swells

So, can this magical bending force have an impact on surface waves?

Yes, the Coriolis effect does have an influence on ocean swells.

However, its impact is subtle and indirect compared to factors like wind patterns, ocean currents, and coastal topography.

Then, here's how it interferes with waves.

1. Wave Generation and Propagation

Ocean swells are primarily generated and driven by wind energy and bottom topography as they approach the shore.

These are undoubtedly the more dominant factors in the creation of waves.

Since the Coriolis effect influences wind patterns (for example, the trade winds and westerlies), we can say it indirectly affects the direction of swell formation and movement.

Swell: only slightly impacted by the Coriolis force | Photo: Shutterstock

2. Swell Refraction Over Long Distances

Also, while waves themselves do not transport mass, the water particles within them move in orbital motions (circles), and these particles do have mass.

As swells travel over vast distances (hundreds to thousands of miles), the Coriolis force causes them to gradually shift in direction.

However, this force is weak because the Coriolis force primarily acts on large-scale, sustained motions rather than oscillatory movements like waves.

The effect, though, is more noticeable in long-period swells traveling across entire ocean basins.

3. Swell Interaction with Currents

The Coriolis effect shapes major ocean currents, such as the Gulf Stream and Kuroshio Current.

When swells encounter these currents, their direction and speed can be altered due to changes in wave energy distribution.

So, ultimately, the short answer is that the Coriolis force is strongest at large scales and is weak on short, fast-moving waveforms like swells.

Therefore, its influence on oceanic wave trains and seaside waves is minimal.


Words by Luís MP | Founder of SurferToday.com



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