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about 8 years ago
Manta Ray hot lunch Marianas Variety (Press Release) — The Manta Ray Band will be having a hot lunch this Saturday, Feb. 6, 2016, to raise funds for their trip to the Tumon Bay Music Festival on Guam next month. The lunches are $5 each and include fried chicken, lumpia (fried spring roll ...
about 8 years ago
gulfnews.com Whale shark sightings along UAE coast not alarming: experts gulfnews.com Dr. Elsayed Ahmad Mohammed, Regional Director, Middle East and North Africa, of International Fund for Animal Welfare (IFAW), told Gulf News that the recent appearances of the fish make sense given the whale shark feeds close to the surface and often ... and more »
about 8 years ago
KHON2 Whale shark surprises tour group off Haleiwa KHON2 A group led by North Shore Shark Adventures was visited by a whale shark Friday morning, the intimate experience captured on video. They were about three miles off Haleiwa when the shark slowly emerged. “It swam right up to the boat, really slow ... and more »
about 8 years ago
Thanh Nien Daily Carcass of beached whale shark to be preserved by Vietnamese scientists Thanh Nien Daily The Nha Trang Oceanography Institute in central Vietnam has decided to preserve the carcass of a whale shark that died after it got caught in a fishing net last week. Fishermen and local authorities on Thursday handed over the dead fish to the institute. Giant whale shark to be embalmed for scientific researchVietNamNet Bridge all 2 news articles ...
about 8 years ago
National Geographic Manta Rays Get Crittercams for First Time Ever National Geographic We didn't think suction cups would work because manta ray skin is really rough like sand paper. We knew suction cups worked well on the smooth skin of whales. The cups were originally designed to move pieces of glass. But we gave it a try, and with a ... Scripps Grad Student Receives Prestigious Environmental FellowshipScripps Oceanography News all 4 news articles » ...
about 8 years ago
Video From a Whale Shark's Point of View National Geographic Their goal was to deploy Crittercams on whale sharks to get a glimpse of the sharks' underwater world and to better understand their behavior along the reef. Like most people, Wilhelm had never seen a whale shark. He worked on the Crittercams for about ... and more »
about 8 years ago
Zap2It Dominic Monaghan on meeting the Whale Shark: 'I had this sort of out of body experience' Zap2It “Wild Things With Dominic Monaghan” returned to Travel Channel with its third season on Wednesday (Jan. 27). The premiere, aptly titled, “Majestic Mozambique,” finds our host on the hunt for the elusive — and quite massive — Whale Shark. Early on in ... Monaghan knows where the 'Wild Things' areVirgin Islands Daily News all 9 news articles ...
about 8 years ago
CBC.ca Brian Keating swims alongside La Paz's mysterious whale sharks CBC.ca They're such huge animals," said Keating, who saw his first whale shark less than 15 minutes out of the bay. By the day's end, Keating had met at least a dozen whale sharks. He even managed to snap a few underwater photos from their tail end as proof.
about 8 years ago
FIS Fishing ban for giant manta ray FIS The Ministry of Production (Produce) has banned the capture of the giant manta ray (Manta birostris) in the Peruvian marine waters, in order to preserve this species on the coast of the country. The measure, established by a ministerial decree, is in ... and more »
about 8 years ago
The National Whale shark seen swimming in Abu Dhabi marina The National ABU DHABI // A whale shark between three and four metres long has been seen swimming in the marina at the InterContinental Abu Dhabi. Employees at the hotel first noticed the fish at 1.45pm on Friday and quickly took a video and photos to capture the ...
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Thursday
Apr012010

I'm surfing on the inside

I've always loved the idea of internal waves; the idea that gentle, rolling, and sometimes very large waves roll along, not on the surface of the sea, but deep below it.  How is that possible?  The best explanation is by analogy:  If you've ever swum in a lake in early summer, where your body was bathed in warm still surface waters but your legs were down in the icy deeper layer, then you've crossed the boundary that internal waves call home.  They travel along "density boundaries" and the most common of those is the bit where water goes from warm at the surface to cold at depths, called the thermocline; there are other types of density boundaries too, such as where fresh water overlies denser briny water.  Sometimes you can even see density boundaries near the surface; the change in density affects the way light passes through the water so you can sometime see a shimmery sort of distortion, even though the water is clear.  There's a good one shown here. The picture at right from the Institute of Hydromechanics at the University of Stuttgart shows an artificial internal wave produced as part of an experiment; they dyed the different densities of water to show it better.

The bigger the change from warm to cold in a thermocline, the bigger the density difference, with the colder water being more dense.  Really sharp thermoclines like this have some interesting properties, such as the ability to reflect some types of sonar.  In fact, Navy submarines have been known to "hide" below a good thermocline, and then be revealed for all to "see", by a passing internal wave.  The sub is below the thermocline one minute, then above it the next, exposed and vulnerable to the next sonar ping - oops. 

Internal waves can even "break", like a surf wave on a beach.  This image from Memorial University in Canada shows a model of how this happens, with the wave coming in from the left and breaking on the bottom as it gets shallower; all the while the water's surface is calm.  The internal wave doesn't look quite the same as a regular beach wave because the density difference isn't nearly as much as when you go from water to air and the internal wave pushes up against the heavy, viscous overlying water, but the principle is the same.

I don't know if its possible to somehow surf on an internal wave.  I doubt it, because the drag of the overlying water would be much more than you would experience in air, but its pretty cool to think about.  Its probably a good thing if you can't do it, because Al surfing is about the only thing scarier than Al dancing...

Reader Comments (1)

Hello! It was a pleasure to read your article, the information provided was of much interest for me. For many years I was afraid to swim due to the fear of depth, but recently I began to resist this weakness and won. Now I am eager to to enjoy the advantages of swimming to the full extent and learn more about this mysterious world.
May 23, 2012 | Unregistered Commenterpdf viewer

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