Rogue waves happen more often than expected by scientists

[tbodine88]

There is a wave monitoring system in the north sea which has shown that rogue waves are common.
https://www.sciencedaily.com/release...1013095756.htm

https://www.sciencedaily.com/release...0308114617.htm

So those stories about rogue waves aren't fallacious!

[dannc]

Interesting, I saw this report about rogue waves recently.

Study Finds Massive Rogue Waves Aren’t as Rare as Previously Thought – gCaptain

Later,
Dan

[Cheechako]

So how much bigger does a wave to be to be called a "rogue"?

[Steadman Uhlich]

Rogue Waves have been an interesting phenomenon and are often attributed to mythical exageration because they are rarely seen.

From my notes on the subject, here is one of the best concise statements I have seen from a scientific journal that points to the reason why they can "appear from nowhere":

'In deep water, where waves are much less regular, you expect a larger wave from time to time. Our paper shows that, in contrast to what was previously thought, if you're the observer on a ship, rather than seeing a gradual build-up of waves, the rogue wave will come seemingly out of nowhere.

'This happens because large waves tend to move to the front of the wave group.'

The research made use of mathematical modelling based on non-linear physics. The investigators used hundreds of simulations of random waves to analyze the differences between linear and non-linear wave dynamics.

Professor Adcock said: 'These findings fit the anecdotal evidence you hear from mariners. They often describe "walls of water" coming at them in the open ocean that are impossible to steer around -- an observation supported by our modelling, which shows that rogue waves tend to have a much broader crest than traditionally predicted by linear theory.

'All of this means that in a very rough storm, you can't simply assume you'll get a warning before a freak wave hits. Seafarers need to be aware that a large wave may appear out of nowhere.'

Story Source:

Materials provided by University of Oxford. Note: Content may be edited for style and length.

Journal Reference:

Thomas A. A. Adcock, Paul H. Taylor, Scott Draper. Nonlinear dynamics of wave-groups in random seas: unexpected walls of water in the open ocean. Proceedings of the Royal Society A: Mathematical, Physical and Engineering Science, 2015; 471 (2184): 20150660 DOI: 10.1098/rspa.2015.0660

[Steadman Uhlich]

Originally Posted by Cheechako

So how much bigger does a wave to be to be called a "rogue"?

I recall reading it is only called a "Rogue" by scientists (oceanographers) when the wave reaches 2x the Significant Wave Height (which is the mean, NOT the average, of the highest 1/3 of the waves in a period).

So, if the SWH is 12 feet (not too unsual in open ocean) the "Rogue" would need to be 24 feet (8 meters). It would definitely "stand out" from the average.

Of course laymen and some typical sailors use the term "Rogue Wave" to describe the occasional splash of green water that wets them in the cockpit.(meant as humor) or topples the wine glass on a catamaran (also for humor).

[redhead]

Thank you. It is gradually coming out of the realm of boogie man/movie plot into the light of science. That never hurts.

[Steadman Uhlich]

I mentioned Signficant Wave Height earlier. I think it is helpful to use an illustration:

[MarkSF]

The term "rogue wave" is totally inappropriate. It's just a simple matter of probability. Occasional waves to double the mean height are to be expected, and are entirely predictable.

[Cheechako]

That's why I asked what rogue means. It seems at sea a couple times a night you get one. Suddenly the boat lifts up, or you get slapped hard out of nowhere.

[Mike OReilly]

I didn’t read the referenced item closely, but what struck me is their so-called “rogue” wave is simply part of the normal distribution of wave pattern that is normal and expected (as Steady Hand notes ).

The report states:

"The Andrea crest height was 1.63 times the significant height (average height of the one third highest waves). Optimal focusing of the Andrea wave showed that the crest could have been even higher and limited by breaking at 1.7 times the significant height. This establishes the greatest height rogues can reach for any given (or forecasted) significant height."

According to NOAA "On average, about 15% of waves will equal or exceed the significant wave height. The highest 10% of waves could be 25-30% higher than the significant wave height. And on occasion (about one per hour) one can expect to see a wave nearly twice the significant wave height.”

So as I read it, their “1.63 over significant height” is completely normal and fully expected.

However … this paper (actually, the reference to the paper) strikes as more interesting, and more concerning:

https://www.sciencedaily.com/release...1216082200.htm

It seems to be based on models, but reports to show how “extreme” waves can form in a non-linear fashion such that they appear to be disconnected to the ‘normal’ wave pattern that exists. In other words, they could be the real “rouge” wave of mariner mythology.

[barnakiel]

But did not they say one in 100.000? 15 waves per minute times 24 hours = 21.600 waves a day.

Then we are likely to get one rouge wave every five days on a crossing and say 5 to 10 rouge or extreme waves on a crossing.

No problem with sea state 3 to 4 meters. What about that day when the waves are 5 to 7 meter tall?

Right/wrong?

barnakiel

[StuM]

Originally Posted by Steady Hand

I recall reading it is only called a "Rogue" by scientists (oceanographers) when the wave reaches 2x the Significant Wave Height (which is the mean, NOT the average, of the highest 1/3 of the waves in a period).

Sorry, but I beg to differ there. In this case, the mean probably IS the average. It's what is most commonly meant by "average" in general usage.

Technically oriented people avoid using the word "average" because it has no specific meaning.

There are actually many "averages", but for practical purpose, there are three primary ones: Mean, Median and Mode. .
.

.
.
.
For those interested, the three common "averages" are:

Mean = the sum of the values of all data points divided by the number of items.
Median = the value of the middle data point (or the mean of the two middle points if there is an even number of points) when the points are sorted by value.
Mode = the most frequently occurring value in the data collection.

[boatman61]

To me a rogue wave is the wave that seems to rise vertically out of the surrounding sea to twice the average height then topple and race towards me.. not nice..

[Steadman Uhlich]

A good detailed article about Rogue Waves can be found at Wikipedia. If you have not read anything recent or at length about Rogue Waves, I recommend this article because it has a mix of science reports, history, and lists several Rogue Waves of very large size and numerous incidents of large ships that were sunk or disappeared, that have now been attributed to Rogue Wave encounters.

Here is an excerpt that I think should interest any sailors:

"It is now proven via satellite radar studies that waves with crest to trough heights of 20 metres (65.6 ft) to 30 metres (98.4 ft), occur far more frequently than previously thought.[36]

It is now known that rogue waves occur in all of the world's oceans many times each day. In 2004 the ESA MaxWave project identified more than ten individual giant waves above 25 metres (82 ft) in height during a short survey period in a limited area of the South Atlantic. The ESA's ERS satellites have helped to establish the widespread existence of these 'rogue' waves.[37][38]

Thus acknowledgement of the existence of rogue waves (despite the fact that they cannot plausibly be explained by even state-of-the-art wave statistics) is a very modern scientific paradigm.[39] It is now well accepted that rogue waves are a common phenomenon. Professor Akhmediev of the Australian National University, one of the world's leading researchers in this field, has stated that there are about 10 rogue waves in the world's oceans at any moment.[40]

Some researchers have speculated that approximately three of every 10,000 waves on the oceans achieve rogue status, yet in certain spots—like coastal inlets and river mouths—these extreme waves can make up three out of every 1,000 waves because wave energy can be focussed.[41]"

SOURCE: https://en.m.wikipedia.org/wiki/Rogue_wave