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Rogue waves Mysterious Ocean Phenomenon
Rogue waves can account for strange ocean disappearances
Unpredictable danger lurks in the deep sea
The story of the Poseidon Adventure begins with an encounter with a huge rogue wave that hits the ship broadside and turns it over and creates an escape adventure where only a handful of survivors escape. Rogue waves are real and some are called solitons and have been photographed from space. Rogue waves are different in that they are the temporary phenomenal superposition of two wave functions of different frequencies that converge and then diverge. They are hard to predict, unlike solitons that persist for long periods. Neither are they mega-tsunamis that have at their root, causes like earthquakes, landslides, volcanoes and impacts. Rogue waves arise and disappear without warning and are capable of swamping, overturning and breaking up the greatest ships we can make. But with modern observation techniques and the understanding of the ocean, we have the ability to predict the possible occurrence of at least some of them.
Recall wave experiments that were done in high school physics class. Two people take a rope into the school hall and both make waves, first in opposing directions and then in the same direction to observe what happens. We all know that opposing waves, or a wave and a trough will cancel, but two similarly aligned waves will enhance and make a momentary super wave. But in all these cases, these waves are moving in opposite directions. What if we could run and experiment where we could run two waves one after another in the same direction but at slightly different speeds with the faster wave catching up to a slow one. What we would get when the two converge, is a super wave that would last considerably longer. Rogue waves are somewhat like this, but in four dimensions; three of space and one of time. In addition, factors exist that don't in the simple rope experiment.
One of these factors are the variable depth of the ocean bottom where we know wave speed can be seen to change. In fact, it is the increasing shallows close to coastlines that will amplify wave height as the slowing water piles up. This was seen during the 2004 boxing day tsunami that was born of a deep sea earthquake. Initial waves were only A few meters in height, but when they hit shores in Malaysia, they ranged up to thirty meters. As the ocean bottom is uneven, we can learn from this why waves can catch up and superimpose one upon another.
What we know about wave formation in the ocean can help us to understand rogue waves. A wave is basically a pulse of energy traveling over the surface of the ocean that can have a variety of sources. It pulse moves away from the source of the energy, usually weather in the atmosphere over the ocean. Water is not moved beyond a circular pattern as the energy pulses through the medium of the water. Thus in the deep ocean, more wave movement occurs along current directions than from waves which are more of a standing energy transfer between huge numbers of water molecules. Like in the rope experiment, a whole lot of smaller waves can combine to make larger ones, which is why large waves have fractal, self affine patterns of smaller waves on it and yet smaller waves on these. Now existing currents can carry a wave form a little, thus speeding it up. Further, if the energy of a wave runs into shallow water, the circular rhythm is broken, the wave slows and the water piles up and crashes, which is why good surf areas exist in Hawaii, S. Africa and Australia and at certain times of the year.
Caught on video, a real rogue wave
Take some of these ideas out to the deep ocean where current carried waves cross the path of non current carried waves. As the current carried waves catch up and cross the path of other waves from slightly different directions, they enhance and produce a super wave that seems to arise out of nowhere, only to dissipate some time later. A ship that happens to met one of these temporary occurrences can suddenly be swamped and broken up in an otherwise normal chop for that location. Waves pulsing at different frequencies may create a series of rogue waves as long as the energy drives them and pulse difference is maintained. These waves will not be successive. There may be relatively calm spots between each one. As far as is known, rogue waves have not been seen in groups of two or more. All instances that have been recorded have been single occurrences.
Another source of rogue waves comes from something akin to the double slit experiment. In the double slit experiment, two slits break up light or waves into two beams or wave groups that create interference patterns of destruction and enhancement. This three dimensional set up is closer to the real world than the simple rope experiment. In the real ocean, the surface is studded with islands that cause waves to wrap around for the same reason that great surf regions are found where land blocks a great expanse of ocean. As the waves wrap around islands, and even shallows in the deep ocean, waves then cross paths that create short length super waves or rogue waves. As we know where these spots are and have a keen weather eye in space, these rogues are easier to predict and avoid. We know when and where they will form and can take evasive action. These waves will pulse on the lee side of waves and shallows and travel considerable distance. They will often come in chains until the energy provided by weather dissipates. The chains are similar to what happens in the wake of a speed boat.
The unpredictable rogue waves can have weather as the trigger behind them. The greater the weather phenomena at the source, the greater the waves are generated out from the storm. But sometimes they can be triggered by a sub-ocean earthquake that has little influence on the coast. However, the long slow waves generated by a large underwater quake can impact existing waves to create a rouge wave. These too are hard to predict except by a risk factor when seismographs pick up the quake and locates the source of trouble. A general alert can be issued and ships can prepare to take the wave head on instead of broadside. Underwater landslides can do the same thing and sometimes not even picked up on a seismograph. The pulse of energy is directed mostly into the water creating a single wave that in a very few cases can be the seed of a mega-tsunami. Any tsunami will have a low profile in deep water, only to rise to gigantic proportions in the shallow coastlines or ocean shallows. As the oceans are not uniformly deep, rogue waves can reach huge proportions briefly in the shallows only to fall off in the deep.
Today, more than ever, we have the means to detect rogue waves and potential rogue waves before they form by observing the waves on the ocean from space and studying weather patterns like hurricanes and typhoons. Using observation combined with knowledge of currents, we can predict when rogue waves are likely to form, their direction and duration. Even so, there are still those who are surprised in the ocean. Given the size of the oceans and the aperiodic observation from moving satellites, some will escape observation until its too late.