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Unstrange Phenomena

18 September 2009

Do You Know What a Dangerous 'Internal Wave' is in the Air or the Ocean?



From Denny: This was new to me. What the heck is an 'internal wave' and why is it important to know about this phenomenon? It's one of those hidden dangers the public isn't aware of when they fly or take an ocean cruise.

These things can get huge, like 1,000 kilometers wide. They can have a tremendous impact upon our Earth's climate and are prevalent in both the oceans and the atmosphere. What they can adversely affect are oil drilling rigs out in the oceans, undersea communications cables, submarines and aircraft in flight.

A recent example of sudden danger that went undetected from radar or a talented pilot was what happened to a Canadian flight in clear skies last year. For absolutely no apparent reason the plane plummeted 2,000 feet in a mere 15 seconds and then an additional 2,000 feet before the pilot was able to right the plane and level off. Passengers and crew were terrified with 10 passengers requiring hospital treatment for injuries.

For the past five years there's been a mechanical engineering professor over at MIT that has been studying this scary phenomenon that can sneak up on us and cause acute damage quickly. This professor, Thomas Peacock, has been figuring out how internal waves form and propagate. For the high brow scientist crowd you can find his latest papers published in a few months in the Journal of Fluid Mechanics.

What do his papers cover? The first one discusses the forms of internal waves that are generated in the oceans. The second one talks about a mystery in a channel of the Hawaiian Islands. Tied to the tides there is something that occurs twice a day here on a regular basis: a focused beam of internal waves. What's peculiar is that the internal wave occurs in the channel yet vanishes as it progresses near the ocean surface.

Researchers want to understand these internal waves to help create better models for climate change. They believe that these internal waves in the ocean are important to the mixing process of carrying warmer surface water to the deep and bringing colder water to the surface. Internal waves are one of the ocean mechanisms that strongly impact Earth's climate. This oceanic mixing rate is the least understood and if studied further could go a long way to creating more accurate climate projections.

So, what is it that bedevils these researchers about internal waves? They have come a long way toward understanding how internal waves are produced. Their next step is figuring out how their energy dissipates. Right now they can account for 20% of the wave "break" but the remaining 80% is still a mystery.

Because there are practical applications for his research, Thomas Peacock has drawn some heavy weight investors, providing funding to aid him in his study: the National Science Foundation, the MIT France Program and the Office of Naval Research.

How do internal waves form in the ocean? One way is when tidal currents pass over a submerged ocean ridge that acts as an obstacle, setting up a disturbance. Powerful storms like hurricanes can produce them too by displacing the ocean surface.

How do internal waves form in the atmosphere? Thunderstorms passing over a mountain range can cause them as in the case of the Canadian flight that was terrified in the example stated above. Those internal waves are label 'mountain waves.'

To help us understand this phenomena better the Discovery Channel has been working on a film with professor Thomas Peacock. They have been filming in Western Australia and the South China Sea. Guess what they will be chasing in the hopes they can film it? It's called a Morning Glory cloud which is a long, narrow cylindrical cloud formation that can span up to hundreds of miles.

Peacock and the film crew hope to 'surf' that cloud in a glider since this is the time of year most conducive to this kind of cloud phenomenon. Like Peacock says, "It's a challenge, to try to be there when it happens," he says. "But it will be a once-in-a-lifetime experience to surf the Morning Glory." Sounds like an extreme sport!
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