Crazy sea monster dog waves

1975165438+1October 10, the American cargo ship Edmund Fitzgerald sank in the lake superior area between the United States and Canada in the storm. This cargo ship is no small thing. Its hull is 220 meters long and 22 meters wide. It is definitely a monster. But it seems that the strong and safe freighter has not stood the test. When the disaster happened, the freighter lost its chance to survive before sending out a distress signal. All the 22 crew members on board were killed and their bodies have not been found so far.

According to the preliminary report of the U.S. Coast Guard, the tragedy occurred due to the negligence of the crew and the failure to cover the hatch safety cover of the cargo ship's top cabin as required. This statement has always been controversial, and many colleagues said that the crew would not be so careless. 20 10 diving detectives put forward another possible cause of the disaster by exploring the underwater situation at the accident site-the cargo ship may have encountered a powerful "killing wave"-crazy dog wave. Perhaps, when the cargo ship was on the water, it was shot in half by this wave.

Lake Superior is the largest freshwater lake in the world, with an area of 82,000 square kilometers and a maximum depth of 405 meters, and its storage capacity accounts for more than half of the entire Great Lakes. On the vast lake, the swells from all directions are fast and slow, pushing and competing with each other, and the energy accumulated underwater sometimes suddenly pushes up the swells. In addition, in winter 1 1, there is less ice on the lake, and it is more prone to sudden surge, resulting in a dog wave that makes people smell pale.

However, it is extremely rare to produce crazy dog waves in lakes, and "mad dogs" prefer to make waves at sea.

Is there a "killing tide"

There have been legends about strange waves at sea since ancient times, and Ernest shackleton, a legendary British explorer, described a thrilling experience of encountering crazy dog waves. 19 16, he sailed from Elephant Island near Antarctica to South Georgia Island in the Atlantic Ocean. He described: "We were driven forward by the undulating waves for several days, but one day, a thin wave emerged from the rough waves." I have been praying that God can protect us and get us through this difficult time. The waves were heavily photographed and our ship was shot down underwater. Under the impact of the surrounding current, the hull kept shaking, but maybe God heard my prayer, and finally our ship escaped the disaster and took us away from the strange waves at sea. "

For the height of this crazy dog wave, people who have seen it can only be described as "very high", and there is no specific data to prove how big the "strange wave" they described is. Therefore, in the past few centuries, people's impression of huge waves only stayed in the "exaggerated" description of survivors, and scientists often disagreed.

Until 1 99565438+1October1,the Drapp Na offshore oil platform on the Norwegian coast in the North Sea experienced a wave of 26 meters high, which was twice as high as other waves around it, and was equivalent to a building with a floor of 10. This time, the laser equipment on the offshore oil platform measured the height of the huge waves, which was more accurate.

People used to think that this abnormal fluctuation only happened once every one million years. However, in 200 1 year, Europe began to implement the "big wave plan", using two satellites of the European Space Agency to study the state of the ocean. Satellites of the European Space Agency emit pulse signals of radio waves. When radio waves reach the sea surface and then reflect back to the satellite, the collected information can be converted into the situation of the sea surface through complex algorithms. Later, the German Earth observation satellite TerraSAR-X was also used to study mad dog waves, and its resolution can reach 1 m, which is more accurate than the previous satellite data. In just three weeks, the "Big Wave Project" found 10 waves with a wave height of more than 25 meters.

These specific figures obtained by scientific means make the "talking about capital" in legends and stories suddenly positioned as a really strange phenomenon, and scientists flock to discuss the formation mechanism of this mad dog tide at major academic conferences.

Do you know mad dog waves?

Crazy dog wave, it is not just a big wave in the ordinary sense like a big wave in a storm. In fact, it is much higher than all other waves around it, and it is a visual effect of "standing out from the crowd" from a height. If defined by precise scientific standards, the wave height of mad dog waves is at least twice that of meaningful waves (waves are actually irregular and consist of waves with different wavelengths, wave heights and steepness. According to observation statistics, the wave height of110 is twice the average wave height, which is called the maximum wave height. The wave height of 1/3 wave is 1.6 times of the average wave height, so many high waves caused by tsunami or typhoon do not belong to crazy dog waves. Crazy dog waves often come unexpectedly, suddenly appear, suddenly disappear, and come and go without a trace.

There are about 50~ 100 shipwrecks in the world every year. Of course, these are not all caused by mad dog waves, but the phenomenon of mad dog waves may help explain some mysterious accidents. Moreover, understanding the formation mechanism of this huge wave is helpful for human beings to make predictions, stay away from dangerous areas and reduce the occurrence of marine tragedies.

However, it is not easy to collect enough effective data. We can't reconstruct the historical information of mad dog waves, and we can only measure the wave height in the nearby waters through the measurement of offshore platforms. Moreover, the waves will move, so it is difficult to track the trajectory of mad dog waves only once in 1~2 minutes.

Because of the lack of data, and the wave-making pool (equipment for simulating waves) can't play the role of simulating crazy dog waves, the only way to study this kind of waves is to place ocean observation equipment in the sea area where crazy dog waves may occur, and wait for rabbits to collect relevant data when crazy dog waves appear. From this point of view, Cape Agus in South Africa is undoubtedly one of the best observation areas. The Indian Ocean and the Atlantic Ocean meet here, and the shipping channel is busy. It has been reported many times that there are waves more than 30 meters high here.

The "roaring westerly belt" from east to west passes through the waters near Cape Aguilar, pushing the waves to move in the same direction, while the Aguilar current moves in the opposite direction. The impact of ocean currents and waves raises the waves and causes huge waves.

Mad dog wave practice

But not all mad dog waves can be explained by the confrontation between these waves and strong ocean currents. Based on the study of crazy dog waves for many years, scientists have given some conjectures that under the action of one or more factors, such a ghostly strange wave may be produced.

Ocean current collision

If the ocean current is in the opposite direction to the main body of the wave, like Cape Aguilar in South Africa, this is not a good thing. The ocean current pushed in the opposite direction will hinder the wave from moving forward, reduce its speed and make the wave surge upward.

But the problem is by no means here. The waves facing the ocean current in front slowed down first, but the waves behind did not slow down. The second wave hits the first wave, and the third wave hits the first two waves. In this way, under the obstruction of the reverse ocean current, several small waves will converge into a big wave, and several waves will be combined to move forward together. Finally, this wave is getting bigger and bigger, which may turn into a huge strange wave.

In addition to the reverse ocean currents, ocean currents in other directions will also gather many small waves from all directions, which will spawn crazy dog waves on the sea surface. However, due to the different velocities and directions of the solitary waves before the collision, the original velocities, waveforms and directions remain after the collision, and the huge waves cannot continue to spread, and will soon disintegrate, and the sea surface will return to calm as if nothing had happened.

The curse of depth change

If a wave originally moves in the deep sea area, but the seabed topography in front rises and the depth of the ocean becomes shallow, then the wave from the deep sea will suddenly be lifted. Water is incompressible, so when waves rush from deeper waters to shallower waters, the only way is to push them up. In some areas on the east coast of the United States, the continental shelf extends far away, and the depth of the seabed will change dramatically, which will lead to higher waves.

Nonlinear irregular wave

As early as the early 1960s, Brooke Benjamin, a physicist at Cambridge University, and Jim Fell, a graduate student, discovered that there were no regular waves in the wave-making pool, and some waves were always bigger than others. That is, using regular wind to make waves or getting irregular waves. In other words, the relationship between the input energy and the generated wave is not linear, but chaotic and nonlinear. These unstable waves can get energy from other nearby waves and quickly form huge crazy dog waves.

Tides add fuel to the flame.

Tidal phenomenon is the periodic movement of seawater under the action of tidal force of celestial bodies (mainly the moon and the sun). Tides change with the position of celestial bodies. For example, at the full moon and the new moon, when the sun, the moon and the earth are in a straight line, the tides will be even greater. When the moon reaches perigee, the spring tide will reach its peak, which is perigee spring tide. The regular fluctuation of this wave may not fully explain the formation of crazy dog waves, but when the moon approaches the moon and sees the spring tide, if the waves are aroused for other reasons, the wave height will be higher and the wave strength will be greater under the pull of huge tidal energy, and the superposition of other factors may become a daunting crazy dog wave.

Predicting crazy dog waves

The progress of modern remote sensing image technology also provides more detailed technical support for the study of mad dog wave. The wave height can be measured more accurately by radar data, and the separation and combination of these waves and ocean currents can be seen more clearly by current technology.

Using various technologies, scientists have jointly developed a "big wave software" that can predict crazy dog waves. It can accurately predict the abnormal changes within 8 kilometers around the ship in 360 degrees and give a warning through radar signals. In this way, with such equipment on board, we can actively monitor the surrounding waters, give the ship a chance to buffer and avoid crazy dog waves. However, because the occurrence of mad dog wave is often in expect the unexpected and its duration is short, it remains to be tested whether such early warning information can effectively reduce the occurrence of tragedy.

The future ocean weather forecast may include mad dog waves, but the occurrence of mad dog waves is more often a random event, and the accuracy of the forecast may be difficult to guarantee. However, it is not a bad thing to have such a forecast to alert people and make preparations in advance.

This article comes from the article of "The Mystery of Big Science and Technology * Science", No.2016 12. Readers are welcome to pay attention to our official WeChat account: hdkj 1997.