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The number of ocean waves in a set

A wave set moves at only half the speed of any individual wave

Ocean waves do come in sets, but not always in sevens.
  • Ocean waves do come in sets, but not always in sevens.
  • Image by Rick Geary

Dear M.A.: Why do ocean waves come in series of seven? And is there any connection between that and the fact that music also comes in seven-note scales (do, re, mi, etc.)? Sting says that "Love is the seventh wave.” What are the other six? And why is his last CD called Ten Summoner’s Tales when there are eleven songs on the CD? Can you think of a good word that rhymes with orange? And why do.... — Basic Anonymous Truthseeker, San Diego

Hold it, hold it, BAT. You’re hyperventilating. Sit down and towel off while the Matthew Alice trauma staff tends to your queries.

Of course, right from the get, you’re headed off into a swamp of misinformation, so before you’re stuck up to your hubs and we have to call in the heavy machinery to tow you, let’s get back on some solid factual ground. Numero uno: Ocean waves do come in sets, but not always in sevens. Or nines, as some people say. Or any particular number. What we see as surf along the shoreline is thousands of miles and many physics lessons away from its origins, probably in mid-ocean.

Consider first that waves actually are just “balls” of stored energy that roll through the water, they don’t actually move the water itself (which explains why a bobbing bit of trash rides up and over a wave as it passes by; the trash moves with the water, which is pushed forward only slightly by the energy of the passing wave). If you’re ready with the Dramamine, let’s take a stab at an explanation of wave sets.

As wind storms blow over the ocean, the drag from friction raises up the water surface into ripples, which grow and move as the wind continues to push on the raised side of the wavelet. Wind energy is transformed into wave energy. Gusty storms generate sets of wavelets of varying sizes, speeds, and directions. Larger, faster waves overtake smaller ones; wave trains moving in different directions intersect one another; wave energy is absorbed or canceled, depending on the particular situation, and eventually there evolves a more orderly system of groups of waves of similar size, speed, and direction. This is what’s known as “swell,” and waves can travel thousands of miles in this form, barring more storms or disruption from bottom features. Actually, waves spread out in arcs as they travel across the ocean, and if there were no land features, they’d eventually form a circle once they’d traveled far enough.

One odd characteristic of these sets of waves is that the entire set moves at only half the speed of any individual wave. This is because the leading wave in a set is continually losing energy as it pushes forward, and it eventually decays. Some of that energy is transferred to the waves behind it. As the first wave disappears, a new wave gradually builds at the back of the set. The number of waves remains the same, but the first and last are always smaller than those in the middle at any given time, and the whole wave set makes slower forward progress than any single wave.

By the time waves reach shallow water, a depth equal to less than half the wavelength, the energy in the wave is distorted by the ocean bottom, and the wave crests and finally breaks. This is a pretty simplified explanation of a complicated energy transfer process, but it demonstrates how unlikely it would be for waves to come in sets of specific numbers.

Having blown your basic theory out of the water, I suppose I could just ignore the rest of your questions, but I didn’t get where 1 am today by being rude to the inquiring public. Well, actually, 1 did — but I guess I’m feeling generous.

Sting’s “seventh wave” is the same fictitious wave to which you referred — the largest of the set. His reference was inspired by a spooky little 1977 Peter Weir movie called The Last Wave, in which Richard Chamberlain plays an Aussie lawyer recruited to defend some aborigines charged with murder. He begins having strange premonitory dreams about a tidal wave and eventually discovers he’s a reincarnated prophet or shaman of some sort, a member of the same ancient spiritual brotherhood as the men he’s defending. Sting’s “seventh wave” seems to be a tidal wave of brotherly love. The other sue apparently are of less interest. The Last Wave is available on videotape if you too would care to be inspired.

The “Summoner’s Tales” peculiarity doesn’t seem to have a logical answer, at least none that the Sting publicity contingent can discover. Of course, “Summoner’s Tales” is a punning reference to Sting’s real name, Gordon Sumner, and “The Summoner’s Tale” from Chaucer’s Canterbury Tales. Had Sting told the truth and called the album “Eleven Summoner’s Tales,” he’d have a title that sounds a little like a box of rocks being dumped down a staircase; “Ten Summoner’s Tales” is much more smoothly poetic though less accurate. That’s sheer speculation on my part, but the answer may be as simple as that. It’s not so unlikely, coming from a man who admits he faked his way through years of Jungian analysis by making up all the dreams he related to his therapist each week.

December 16 update

Ed Lucas from Clairemont supplies the obvious answer to the ten/eleven Summoner’s Tales contradiction. The 11th song on the CD is an epilogue, a literary device found several times interspersed among the stories in The Canterbury Tales. Could the answer have been any clearer? Probably not.

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