FYFD

Tag: ocean waves

  • Rocking From The Waves

    Rocking From The Waves

    Not all seismic activity stems from earthquakes. In fact, much of Earth’s measured seismic waves come from interactions of the ocean and atmosphere with solid ground. Some of the strongest vibrations come from interactions of ocean waves, which transmit pressure waves that don’t attenuate with depth before passing into the solid Earth.

    How those waves propagate and scatter inside the Earth has been a matter of contention for decades, but recent simulations are beginning to uncover the mechanisms that lead to the waves seismologists measure. (Image credit: I. Mingazova; via Physics Today)

  • Internal Waves in the Andaman Sea

    Internal Waves in the Andaman Sea

    Differences in temperature and salinity create distinct layers within the ocean. When combined with flow over submerged topography — underwater canyons, mountains, and reefs — it makes waves. But those waves aren’t always apparent when sitting at the surface. Instead, they travel along those ocean layers as internal waves that can be as tall as hundreds of meters in height.

    When the sun glints just right off the ocean, these massive internal waves can be caught by satellite imagery, as shown in the above image of the Andaman Sea near Thailand and Myanmar. Even seemingly calm waters can roil in the deep. (Image credit: USGS; via NASA Earth Observatory)

  • Submarine Canyons Focus Waves

    Submarine Canyons Focus Waves

    In winter months Toyama Bay in Japan can get hammered by waves nearly 10 meters in height. These waves, known as YoriMawari-nami, pose dangers to both infrastructure and citizens, and, thus far, are not captured by typical forecasting models.

    A new study indicates that these waves have their origin in the particular topography of Toyama Bay and the physics behind the double-slit experiment. The shape of Toyama Bay is such that only waves from the north-northeast can propagate all the way to shore. That restriction essentially creates a single, coherent source for waves in the bay.

    The bay is also home to submarine canyons that stretch like underwater valleys from the continental shelf down toward the deeper ocean. To the incoming waves, these canyons act much like the slits in the double-slit experiment, creating two sets of waves whose fronts can interfere. In some positions, a wave crest will combine with a wave trough, cancelling one another out. But in other spots, two wave crests will meet and combine, creating the much larger YoriMawari-nami wave.

    Diagram illustrating the similarity of the YM-wave phenomenon to Young's double-slit experiment. By H. Tamura et al.

    Toyama Bay is not the only spot in the world where this phenomenon happens. The same physics is behind some of the most popular surf spots in the world, including Half-Moon Bay in California and Nazaré, Portugal. In all of these cases, properly predicting wave heights requires tracking an extra variable — wave phase — that most models leave out. That’s why forecasters have struggled with Toyama Bay’s waves. (Image credit: wave – M. Kawai, diagram – H. Tamura et al.; research credit: H. Tamura et al.; via AGU Eos; submitted by Kam-Yung Soh)

  • Testing Waves in High Gravity

    Testing Waves in High Gravity

    Where waves crash and meet, turbulence is inevitable. But exactly how large waves interact — whether in the ocean, in plasma, or the atmosphere — is far from understood. A new experiment is teasing out a better physical understanding by tweaking a variable that’s been hard to change: gravity.

    To do so, the researchers conduct their experiments in a large-diameter centrifuge (shown above) where they can create effective gravitational forces as high as 20 times Earth’s gravity. This increases the range of frequencies where gravity-dominated waves occur by an order of magnitude.

    By studying this extended frequency range, the authors found something unexpected: the timescales of wave interactions did not depend on wave frequency, as predicted by theory. Instead, those interactions were dictated by the longest available wavelength in the system, a parameter set by the size of the container. It will be interesting to see if future work can confirm that result with even larger containers. (Image credit: ocean waves – M. Power, others – A. Cazaubiel et al.; research credit: A. Cazaubiel et al.; via APS Physics; submitted by Kam-Yung Soh)

  • Featured Video Play Icon

    “Mocean”

    Ocean waves are endlessly fascinating to watch. In “Mocean,” cinematographer Chris Bryan captures them in ways few ever see, thanks to his high-speed camera. Honestly, this film is so gorgeous that I don’t want to distract you with the science, so just go watch!

    …

    All done? Pretty wonderful, right? There’s nothing quite like seeing those holes break and expand through sheets of water, tearing what looked solid into a spray of droplets that bleed salt into the atmosphere. Or how about those rib vortices underneath the waves? Or the cloud-like turbulence of the waves breaking overhead? How fortunate we are to see and capture and share such beauty! (Video and image credit: C. Bryan; via RedShark; submitted by Michael F.)

  • Reader Question: Cross Sea

    Reader Question: Cross Sea

    Reader Matt G asks:

    [What’s] going on here?

    Why’s the pattern square? Just a special case of waves traveling in different directions, and this photo happened to catch some at right angles to one another?

    You’re not far off, Matt! This is an example of cross sea, where wave trains moving in different directions meet. Like most ocean waves, these waves originated from wind moving over the water. As the wind blows, it transfers energy to the water, disturbing what would otherwise be a smooth surface and setting up a series of waves. Oftentimes, these waves can outlast the wind that generates them and travel over long distances of open water as a swell.

    Cross seas occur when two of these wave systems collide at oblique angles. They’re most obvious in shallow waters like those seen here, where the depth makes their criss-cross pattern clearer. Another name for them is square waves, and although the pattern isn’t a perfect square, it’s usually fairly close. If the waves aren’t separated by a large angle, they’re more likely to merge than to create this sort of pattern.

    Neat as cross seas look, they’re quite dangerous, both to ships and swimmers. Ships are built to tackle waves head-on and don’t fare well when they’re forced to take waves from the side. For swimmers, the danger is a little different. Cross seas create intense vorticity under the surface and can generate stronger than usual riptides that sweep the unwary out to sea. (Image credit: M. Griffon)

  • The Drama of Turbulence

    The Drama of Turbulence

    Photographer Jason Wright captures dramatic views of Hawaiian landscapes. Moments like these remind us of the spectacular power of the ocean and atmosphere around us. Just look at all that incredible turbulence! See more of Wright’s work on his Instagram and website. (Image credit: J. Wright; via Colossal)

  • Reader Question: White Caps

    Reader Question: White Caps

    Reader eclecticca asks:

    I really like the last two posts about waves, and they left me with another question…  My dad had a little boat he used to take us ocean fishing on quite a bit.  I always noticed that some days we just had big waves (swells) when out from the coastline and in fairly deep water (a hundred feet to hundreds of feet according to the depth sounder) and other days those swells would “break” and curl and foam and crash in on themselves, being what we called “breakers” or “white caps”.  There is no shore to create the breakers in this case, so what is happening?  Is it due to wind? current  a combination of factors?    Always been kind of curious about this really…

    You’re exactly right: those open ocean white caps are due to wind. Strictly speaking, the wind is what’s causing all* of the waves out in open, deep waters. But once the wind is strong enough, it starts breaking up the crests of waves, creating those foamy white tops. 

    According to one study, the break-up happens when the wind transfers more energy to the wave than surface tension can withstand. When the wave crest breaks up into a mixture of air, spray, and foam, it effectively gives the wind more surface area to push against and continue transferring energy. (Image credit: M. Moers)

    * With a few notable exceptions, like in the case of a tsunami.

  • Reader Question: Waves Breaking

    Reader Question: Waves Breaking

    As a follow-up to the recent waves post, reader robotslenderman asks:

    What does it look like when the wave breaks? And why do waves sometimes push us back? Why are we able to ride them?

    I wasn’t able to find an equivalent breaking wave version of that dyed wave – side note: readers with flumes, please feel free to make one and share it! – but here’s an undyed breaking wave for our reference.

    Waves break, or get that white, frothy look, when they reach shallower water. In the previous post, the waves we saw were effectively deep-water waves, so they didn’t change in height as they rolled across the tank. Here there’s an incline to simulate a beach, which causes the water to slow down and steepen. That forms the characteristic curl of a plunging breaker, seen here.

    At the beach, a wave runs out of water to pass through and all the energy that wave was carrying has to go somewhere. Some is lost as heat, some turns into the sound of that classic crashing wave, and a lot of it gets dissipated as turbulence that pushes us, sand, shells, and anything else its way.

    As for why we can ride waves, there’s some special physics at play when it comes to surfing. To catch a wave, a surfer has to paddle hard to get up to the wave’s speed just as it reaches them. Too slow and the wave will just pass them by, leaving them bobbing more or less in place. (Image credit: T. Shand, source)

  • Hiding From Waves

    Hiding From Waves

    Ocean waves can be dangerous for boats, particularly when operating near off-shore platforms. But a new study, inspired by electromagnetic waveguides, demonstrates a lab-scale water waveguide capable of damping out a range of waves experienced by any ship inside its protected area. The water waveguide sits below the surface, changing the water depth and therefore the propagation of surface waves. 

    When properly positioned, the waveguide nearly eliminates wave motion in a protected channel. You can see this in the right image, where waves are clearly present in the foreground but the toy boat hardly moves. Contrast this with the image on the left, where the boat bobs and rocks under the same wave conditions without the waveguide. The researchers hope their waveguide concept can help protect ships in wharves and harbors soon. (Image and research credit: S. Zou et al.; via APS Physics; submitted by Kam-Yung Soh)