From johnw@cpg.com Thu Jan 16 02:43:27 1997 Newsgroups: alt.surfing Subject: simple question From: John Webster Date: Thu, 16 Jan 1997 01:43:27 GMT I was jus' wondering: Why do the bigger waves come in sets? Seriously. I've been surfing for about seven years now (with some landlocked periods) and I don't think I've ever read or heard an explanation. Actually I don't think I ever asked anyone before. I know bigger waves have longer periods, and I'm familiar with how the wave forms in relation to depth, and concentration of energy as it approaches shallow water, but sets? I know all about bigger sets first hand, experientially, and resulting hold-downs, etc., but I don't know why the waves come in sets. Why are the smaller waves and bigger waves organized in such a semi-regular alternating fashion? Some bigger, then some smaller, bigger, smaller. Thanks for any info. I won't sleep until a find an answer...I might surf, tho. --John W. johnw@cpg.com From jrisher@epg.sdd.hp.com Thu Jan 16 21:11:30 1997 Newsgroups: alt.surfing Subject: Re: simple question From: "Jeremy Risher (Seed)" Date: Thu, 16 Jan 1997 12:11:30 -0800 John Webster wrote: > Why do the bigger waves come in sets? Seriously. I've been surfing for In a possibly related question... why does wind come in gusts? -jeremy From tbmaddux@alumnae.caltech.edu Fri Jan 17 00:55:48 1997 Newsgroups: alt.surfing Subject: Re: simple question From: tbmaddux@alumnae.caltech.edu (Timothy B. Maddux) Date: 16 Jan 1997 23:55:48 GMT In article <32DE8B72.3C73@epg.sdd.hp.com>, Jeremy Risher (Seed) wrote: >In a possibly related question... why does wind come in gusts? They're really two different phenomena. Ground-level winds are turbulent, meaning they vary randomly around a mean value. A gust is a high-speed fluctuation of wind velocity. Gusts don't group together in the same way that larger waves do. -- .-``'. Timothy B. Maddux, Ocean Engineering Lab, UCSB .` .`~ http://www.engineering.ucsb.edu/~tbmaddux/ _.-' '._ "From the essence of pure stoke springs all creation." From johnw@cpg.com Thu Jan 16 21:49:28 1997 Newsgroups: alt.surfing Subject: Re: simple question From: John Webster Date: Thu, 16 Jan 1997 20:49:28 GMT John Webster wrote: > Why do the bigger waves come in sets? Seriously. Yes, I will now compose my own thread based on this question that some may have found too ridiculously fundamental to bother with. I'm guessing that the waves come in sets because, just as there are swells that alternate in size, there are longer frequency waves that vary in size, producing larger swells every few minutes. This my sound simplistic, and I may be thinking too hard about it (ouch -- my brain hurts :-)), but hey, humor me will ya? Even in the form of a flame. I haven't surfed in like 3 months due to knee injury, death of my car, and flu, perhaps that's why this question is giving me so much trouble... --John W. johnw@cpg.com *** rydesydewayzallwayzstreetsnowh2o *** From tbmaddux@alumnae.caltech.edu Fri Jan 17 00:50:26 1997 Newsgroups: alt.surfing Subject: Re: simple question From: tbmaddux@alumnae.caltech.edu (Timothy B. Maddux) Date: 16 Jan 1997 23:50:26 GMT In article <32DD87BF.446B@cpg.com>, John Webster wrote: >Why do the bigger waves come in sets? Longer waves travel at faster speeds than shorter waves. As the waves move across the ocean, those of similar wavelength form groups that travel together. These groups of waves are what we experience as sets. A group has a series of waves in it, with smaller waves leading and trailing and the largest waves in the group in the middle. As the group comes ashore, the smallest waves of the group are the first to break. Then the set peaks out with the largest waves, followed by a few smaller ones. Sets are rare because the longest and largest waves are statistically rarely produced by winds. If you ever get a chance to see a deep-water wavemaker, take it. Waves have all kinds of cool properties [grouping being one neat thing] that we don't always see as surfers. -- .-``'. Timothy B. Maddux, Ocean Engineering Lab, UCSB .` .`~ http://www.engineering.ucsb.edu/~tbmaddux/ _.-' '._ "From the essence of pure stoke springs all creation." From b.rainwater@worldnet.att.net Fri Jan 17 03:54:53 1997 Newsgroups: alt.surfing Subject: Re: simple question From: Robert Rainwater Date: Thu, 16 Jan 1997 18:54:53 -0800 Timothy B. Maddux wrote: > > Longer waves travel at faster speeds than shorter > waves. What do you mean by 'longer' waves? From tbmaddux@alumnae.caltech.edu Fri Jan 17 08:40:04 1997 Newsgroups: alt.surfing Subject: Re: simple question From: tbmaddux@alumnae.caltech.edu (Timothy B. Maddux) Date: 17 Jan 1997 07:40:04 GMT In article <32DEE9FD.68FE@worldnet.att.net>, Robert Rainwater wrote: >I wrote: >> >> Longer waves travel at faster speeds than shorter >> waves. > >What do you mean by 'longer' waves? By that I mean waves with longer distances from crest to crest. A wave with a longer wavelength has a longer period and shorter frequency. It also is larger (for a given height) when it breaks than a shorter wave. It's also true that larger waves (waves with greater heights) travel faster than smaller waves, but the effect is not as great. I didn't mention it as the previous poster already had. -- .-``'. Timothy B. Maddux, Ocean Engineering Lab, UCSB .` .`~ http://www.engineering.ucsb.edu/~tbmaddux/ _.-' '._ "From the essence of pure stoke springs all creation." From keensurf@no.spam.cts.com Sun Jan 19 10:09:38 1997 Newsgroups: alt.surfing Subject: Re: simple question From: keensurf@no.spam.cts.com (Thomas Keener) Date: Sun, 19 Jan 1997 09:09:38 GMT tbmaddux@alumnae.caltech.edu (Timothy B. Maddux) wrote: >Longer waves travel at faster speeds than shorter >waves. As the waves move across the ocean, those >of similar wavelength form groups that travel >together. These groups of waves are what we >experience as sets. >A group has a series of waves in it, with smaller >waves leading and trailing and the largest waves >in the group in the middle. As the group comes >ashore, the smallest waves of the group are the >first to break. Then the set peaks out with the >largest waves, followed by a few smaller ones. >Sets are rare because the longest and largest waves >are statistically rarely produced by winds. >If you ever get a chance to see a deep-water >wavemaker, take it. Waves have all kinds of >cool properties [grouping being one neat thing] >that we don't always see as surfers. Tim, since you are associated somehow with UCSB's Ocean Engineering Lab, I have to give you _some_ credibility. But a lot of what you say is misleading. Grouping is an open ocean phenomenon. Surf sets are caused in large part by interference from other swells. And since there is wind in so many places in the world, causing swells so much of the time, sets are extremely common. The only time you don't see sets is when one swell totally overpowers any other swell. As you say, longer (larger) waves travel faster. So they are at the front of a swell. In any particular set the larger waves are usually in the middle, but the larger sets are usually at the beginning of a swell. What 'deep-water wavemaker' are you talking about? And how does it differ from blowing on a calm swimming pool? Mind, I ain't no scientist. I've just spent a hell of a lot of time staring at the ocean. -- TomK keensurf@cts.com From ptomlin@aol.com Mon Jan 20 19:48:04 1997 Newsgroups: alt.surfing Subject: Re: simple question From: ptomlin@aol.com Date: 20 Jan 1997 18:48:04 GMT In article <32DD87BF.446B@cpg.com>, John Webster writes: >I was jus' wondering: >Why do the bigger waves come in sets? Now I've read all the replies on this thread, I'm more confused than before. I think you are over complicating things. My theory is based on what happens when you mix sound waves. Big waves travel quicker than little ones, Yes? Waves coming ashore consist of a number of swells of differing direction, size and wavelength. OK so far? Heard of interference patterns? So this is what I think: Waves, from one swell source head toward the shore. At the same time waves from a different swell source are doing the same thing, but the waves are a different size (so they are going at a different speed). <<< These different swells could be generated by the same weather system. As it tracks across the ocean, changing direction, getting deeper,etc >>> At one point, the peaks of the waves from each swell are in synch; so they add together (ie double up).This is the set. As the waves get progressively out of sych, they waves get smaller; until the peaks of one swell coincide with the troughs of the other. When this happens, they cancel each other out; this is a lull. Easy ain't it? This would explain why you get different numbers of waves in a set and different times between sets. If the two swells were very similar in size then they would stay in synch longer; hence more waves to a set and less time between sets. If the two swells were more different then you would have to wait longer between sets and there would be less waves to each set. With a wave editor like Cool Edit, try mixing a sine wave of 220Hz with one of 230Hz. Look at the waveform window, zoom in if you can't see detail. What do you see? Sets, thats what. Is this all Bullshit? Tell me? -------------------------------------------------------------------------- Gadget Bude, Cornwall, UK e-mail: ptomlin@aol.com "Modesty in delivering our opinions leaves us the liberty of changing them without humiliation." -------------------------------------------------------------------------- From ric@discoveryinternational.com Wed Jan 29 01:54:07 1997 Newsgroups: alt.surfing Subject: Re: simple question From: ric@discoveryinternational.com (Ric Harwood) Date: Wed, 29 Jan 1997 00:54:07 GMT In alt.surfing, <19970120184800.NAA02771@ladder01.news.aol.com>, ptomlin@aol.com, ptomlin@aol.com wrote: >I think you are over complicating things. More like over simplifying things... There are so many different processes occurring similtainiously. > My theory is based on what >happens when you mix sound waves. You are thinking of only one of the processes. >Big waves travel quicker than little ones, Yes? Yes, though don't forget that waves can be 'big' in different ways. Height - obviously. Period - wavelength - speed - energy, are related to each other. Longer period waves have more energy, and this translates to 'bigger' when they break. >Waves coming ashore consist of a number of swells of differing direction, >size and wavelength. >OK so far? >Heard of interference patterns? This is what Tom was referring to. It is a significant factor here in the UK. Tim is talking about 'grouping' where sets form in deep water as a feature of the way that the wave energy moves through the water. If you look long and hard enough at the equations it is clear that waves moving as groups and moving forwards through the group is just the way it should be. However I have yet to find anyone who can put it into words clearly. I do not quite know if the following is true, or just another metaphor, but it works for me. It is probably somewhere in between, like all the other explanations. If you think that the water in front of the first wave is stationary, as the first wave moves into this flat water some of it's kinetic energy is converted into potential energy, in raising the water level against gravity. In this way the front wave dies out. The following wave has less work to do, so it is bigger, but it too passes some potential energy into kinetic, and it too gets smaller. As the front wave is fully converted into potential energy the second wave becomes the front wave, and so on. Behind the group the water becomes flat, again as the potential energy of the last wave is changed back to kinetic energy. The wave moves forwards through the group. Another feature of groups is that they cause a raised water surface level where the group is, and a corresponding drop, in the gap before the next set. This sequence develops an underlying long period wave, with a wavelength equal to the distance between sets. It is termed an "infra-gravity wave". [Those we think of as waves are termed 'gravity' waves.] When the waves move from 'deep' into 'shallow' water they don't move in groups in quite the same way, but they retain the same group formation that they had before the transition. What also happens at this time is that the gravity waves become separated from the infra-gravity waves. Even if there is only one [dominant] wave train/swell you then do have two waves, one an order of magnitude longer than the other. These will interact as you suggest, enhancing causing the "sets" that we perceive on the beach. [Depending on who you ask.] Clear as Mud now? Ric. -- EuroSurf forecasts: http://www.discoveryinternational.com/ric/surf.htm PGP public Key ID: 0766ABE5 From tsulaiti@slonet.org Wed Jan 29 04:41:54 1997 Newsgroups: alt.surfing Subject: Re: simple question From: Tauras Date: Tue, 28 Jan 1997 19:41:54 -0800 Ric Harwood wrote: > > In alt.surfing, <19970120184800.NAA02771@ladder01.news.aol.com>, > ptomlin@aol.com, ptomlin@aol.com wrote: > > >I think you are over complicating things. > > More like over simplifying things... There are so many different > processes occurring similtainiously. > > > My theory is based on what > >happens when you mix sound waves. > > You are thinking of only one of the processes. > > >Big waves travel quicker than little ones, Yes? > > Yes, though don't forget that waves can be 'big' in different ways. > Height - obviously. > Period - wavelength - speed - energy, are related to each other. > Longer period waves have more energy, and this translates to 'bigger' > when they break. > > >Waves coming ashore consist of a number of swells of differing direction, > >size and wavelength. > >OK so far? > >Heard of interference patterns? > > This is what Tom was referring to. It is a significant factor here in > the UK. > > Tim is talking about 'grouping' where sets form in deep water as a > feature of the way that the wave energy moves through the water. > > If you look long and hard enough at the equations it is clear that > waves moving as groups and moving forwards through the group is just > the way it should be. However I have yet to find anyone who can put > it into words clearly. > > I do not quite know if the following is true, or just another > metaphor, but it works for me. It is probably somewhere in between, > like all the other explanations. > > If you think that the water in front of the first wave is stationary, > as the first wave moves into this flat water some of it's kinetic > energy is converted into potential energy, in raising the water level > against gravity. In this way the front wave dies out. > The following wave has less work to do, so it is bigger, but it too > passes some potential energy into kinetic, and it too gets smaller. > As the front wave is fully converted into potential energy the second > wave becomes the front wave, and so on. > > Behind the group the water becomes flat, again as the potential > energy of the last wave is changed back to kinetic energy. The wave > moves forwards through the group. > > Another feature of groups is that they cause a raised water surface > level where the group is, and a corresponding drop, in the gap before > the next set. This sequence develops an underlying long period wave, > with a wavelength equal to the distance between sets. It is termed an > "infra-gravity wave". > [Those we think of as waves are termed 'gravity' waves.] > > When the waves move from 'deep' into 'shallow' water they don't move > in groups in quite the same way, but they retain the same group > formation that they had before the transition. > What also happens at this time is that the gravity waves become > separated from the infra-gravity waves. Even if there is only one > [dominant] wave train/swell you then do have two waves, one an order > of magnitude longer than the other. These will interact as you > suggest, enhancing causing the "sets" that we perceive on the beach. > [Depending on who you ask.] > > Clear as Mud now? > > Ric. > > -- > EuroSurf forecasts: http://www.discoveryinternational.com/ric/surf.htm > PGP public Key ID: 0766ABE5 Just as I suspected. Waves are mysterious but their nature reveals itself to those that look beyond, and grasp the sine by the horns. I did a summary of basic wave theory in simple posting at the: http://www.callamer.com/~surftime/Features/saftey.html Yes life is full of typos but true understanding comes to one that has an open mind and an inquisitive soul. Enjoy the ride and keep it mysterious, or else everybody will start surfing. Very nice sunset session as our swell clocks NW and offshores continue to blow 70 degree wind up the wave face drying the tongues hanging out of each person taking the drop at our new river mouth break. Strange how the rains can create new breaks as dry creeks become ragging rivers and all we can do is ride and :) >>>>>>Sig back by popular demand<<<<<<<< Tauras Sulaitis Current Project: Toobs Inc. USTA Design Inc. surftime@callamer.com tauras@lietuva.com http://www.callamer.com/~surftime/ West Coast Sty http://www.slonet.org/~tsulaiti/ East Coast Sty http://www.minds-online.com/sty/ ***Warning*** Personal Site with typos, but they are really just a combination of my phonetic heritage clashing with my native tongue! From johnw@cpg.com Wed Jan 29 17:31:03 1997 Newsgroups: alt.surfing Subject: Re: simple question From: John Webster Date: Wed, 29 Jan 1997 16:31:03 GMT Ric Harwood wrote: > > In alt.surfing, <19970120184800.NAA02771@ladder01.news.aol.com>, > ptomlin@aol.com, ptomlin@aol.com wrote: > > >I think you are over complicating things. > > More like over simplifying things... There are so many different > processes occurring similtainiously. < snip yet more interesting info > Gee, maybe I should have labelled my original post "complex question?" ;^D Much good reading here. And I thought it might have been a dumb question... --John W. johnw@cpg.com *** ryde * syde * wayz * on * wave * pro * pa * ga * tion *** From a.best@barnsley.ac.uk Fri Jan 31 11:26:24 1997 Newsgroups: alt.surfing Subject: Re: simple question From: fishy Date: Fri, 31 Jan 1997 10:26:24 +0000 John Webster wrote: > > Ric Harwood wrote: > > > > In alt.surfing, <19970120184800.NAA02771@ladder01.news.aol.com>, > > ptomlin@aol.com, ptomlin@aol.com wrote: > > > > >I think you are over complicating things. > > > > More like over simplifying things... There are so many different > > processes occurring similtainiously. > > < snip yet more interesting info > > > Gee, maybe I should have labelled my original post "complex question?" > ;^D > > Much good reading here. And I thought it might have been a dumb > question... > > --John W. > johnw@cpg.com > > *** ryde * syde * wayz * on * wave * pro * pa * ga * tion *** Maybe when I posted my thoughts I should have made a point about breaking waves and the effects of friction (remember that post right at the start) then the topic could of been even more detailed. I think my original posting was a little short (I feel I ought to say that I did know about different swell frquencies but couldn't be arsed writing it all down) From ric@discoveryinternational.com Sat Feb 01 17:45:18 1997 Newsgroups: alt.surfing Subject: Re: simple question From: ric@discoveryinternational.com (Ric Harwood) Date: Sat, 01 Feb 1997 16:45:18 GMT In alt.surfing, <32F1C8D0.549A@barnsley.ac.uk>, fishy , fishy wrote: >Maybe when I posted my thoughts I should have made a point about >breaking waves and the effects of friction (remember that post right at >the start) then the topic could of been even more detailed. WRT frition with te sea bed, [which we have setablished is not responsible for sets] : Bear asked: > why does the shelf slow down waves so much (chronically > so in much of the UK!) ? I mean I understand the drag forces > applying once they are near a break, but in several fathoms??? It A 12 second wave feels the bottom in 112 meters of water. This happens 70 miles offshore from Newquay, which makes quite a difference. To the Gower it is probably 3-4 times that. For an 8sec wave this happens at about 20 miles out from Newquay. Can someone say how far from Hawaii or Cali that this happens? > seems that u/w channels make/allow swells to bend and turn...as in > the St.George that allows surf to reach the Lleyn peninsula. But It does. > if the energy that constitutes a wave is only, say, as far under > the surface as it is above it.... The bottom of the wave is considered to be at a depth of half the wavelength. 12 second wave L=225m, so 'level of no motion'=112m When the depth drops to that of the 'level of no motion' the wave is no longer moving in "deep" water and will lose energy by friction, and be steered by the sea bed, [by refraction, like you can sea near the beach.] A 16 second wave, [rare, but we do see them here in the bigger storms] will feel the bottom at the edge of our continental shelf, 200NM from Cornwall! Regards, Ric. -- EuroSurf forecasts: http://www.discoveryinternational.com/ric/surf.htm PGP public Key ID: 0766ABE5 From tbmaddux@alumnae.caltech.edu Tue Jan 21 19:51:13 1997 Newsgroups: alt.surfing Subject: Re: simple question From: tbmaddux@alumnae.caltech.edu (Timothy B. Maddux) Date: 21 Jan 1997 18:51:13 GMT In article <5bsoi4$qtt@bogus.cts.com>, Thomas Keener wrote: >Grouping is an open ocean phenomenon. Yes, grouping is an open ocean phenomenon, but I maintain that its effects are carried into shallow water... particularly the association of waves of similar size with each other and the way a set will start off small, peak, and fade back into smallness again. [ I wrote: ] >>Sets are rare because the longest and largest waves >>are statistically rarely produced by winds. [ and he responded: ] >Surf sets are caused in large part by >interference from other swells... sets >are extremely common. The only time >you don't see sets is when one swell >totally overpowers any other swell. My statement was misleading. Sets of all sizes are always rolling in. I should have said "the largest sets are rare because..." I slipped into thinking of sets as describing only the big stuff, the ones you have to wait 5-30 minutes for. I disagree with the statement that sets are caused in large part by wave-wave interference. Here in S.B. we get very even swell lines, with little chance for wave-wave interference from multiple sources due to blockage from coastline curves and islands. I still see sets even on a swell that the CDIP wave gage array maps energy on to within a +/- 5 degree bandwidth. >In any particular set the larger waves are usually in the middle, but >the larger sets are usually at the beginning of a swell. Yes, an excellent point. >What 'deep-water wavemaker' are you talking about? >And how does it differ from blowing on a calm swimming pool? A wavemaker is any machine that makes waves... a deep water wavemaker is one that makes waves in water that is relatively deep. In our lab's case, it is a styrofoam block with curved front surface that moves up and down at one end of a tank, causing waves to propagate away from it. Blowing on a swimming pool will produce a whole spectrum of little ripples. Our lab has a couple of 10' diameter turbines to do that, too. The wavemaker can produce much more easily- controlled waves. You can see the group velocity, btw, by throwing a rock in that calm swimming pool and watching the leading edge of the ripples that are created. -- .-``'. Timothy B. Maddux, Ocean Engineering Lab, UCSB .` .`~ http://www.engineering.ucsb.edu/~tbmaddux/ _.-' '._ "From the essence of pure stoke springs all creation." From ptomlin@aol.com Wed Jan 22 18:20:13 1997 Newsgroups: alt.surfing Subject: Re: simple question From: ptomlin@aol.com Date: 22 Jan 1997 17:20:13 GMT Timothy B. Maddux writes: >I disagree with the statement that sets are caused >in large part by wave-wave interference. Here in >S.B. we get very even swell lines, with little chance >for wave-wave interference from multiple sources due >to blockage from coastline curves and islands. Good point. Here in North Cornwall, our swell window is fairly wide. It's about 48 degrees to the South-West. Unfortunately the majority of swell comes from the North-West, that's blocked by Ireland. The big continental shelf (over 200 miles) doesn't help matters. OK, back to the point. I kinda think you don't need multiple sources. Going back to my sound wave analogy, think about strumming a chord on a guitar. You've got six individual waves emanating from a single source. Couldn't that happen with a storm at sea? Try generating some tones in Cool Edit (Shareware). Choose a Base sine wave of, say 220Hz (choppy slop, eh?). Bang in 5 frequency components at 1.1, 1.2, 1.3, 1.4, and 1.5 times the freq. of the base wave. Et voila, check the display. If properly cooked you should have a repeating sequence of waves; 3 set waves interspersed with 12 smaller waves. It has a nice warblie sound too! I kinda like the idea of the swell warbling to us, in a freqency so low, we can ride it. Couldn't a weather system produce a bunch of waves at slightly different frequencies. Oh! Hang on a minute! That was what you were saying a few posts ago, wasn't it? If this is all total bollocks, then tell me to shut up. It's not as if, all this empirical reasoning is very scientific. You're the one with the letters. I suppose, it's a question that doesn't really need answering anyway. The waves will still keep coming in sets, whether we understand them or not. -------------------------------------------------------------------------- Gadget Bude, Cornwall, UK e-mail: ptomlin@aol.com AKA Ball of Confusion -------------------------------------------------------------------------- From tbmaddux@alumnae.caltech.edu Tue Jan 28 05:50:09 1997 Newsgroups: alt.surfing Subject: Re: simple question From: tbmaddux@alumnae.caltech.edu (Timothy B. Maddux) Date: 28 Jan 1997 04:50:09 GMT In article <19970122172000.MAA10257@ladder01.news.aol.com>, wrote: >Couldn't a weather system produce a bunch of waves at slightly different >frequencies. Oh! Hang on a minute! That was what you were saying a few >posts ago, wasn't it? Yes. You can see this mathematically by just adding two waves of very close frequency together and doing the trig. identities. You can hear this on a piano with a black key and a white key right next to each other (I'm not a musician, so I don't know the.. uh.. words)... or with your newfangled computer. -- .-``'. Timothy B. Maddux, Ocean Engineering Lab, UCSB .` .`~ http://www.engineering.ucsb.edu/~tbmaddux/ _.-' '._ "From the essence of pure stoke springs all creation." From ric@discoveryinternational.com Wed Jan 29 01:54:04 1997 Newsgroups: alt.surfing Subject: Re: simple question From: ric@discoveryinternational.com (Ric Harwood) Date: Wed, 29 Jan 1997 00:54:04 GMT In alt.surfing, <19970122172000.MAA10257@ladder01.news.aol.com>, ptomlin@aol.com, ptomlin@aol.com wrote: >Timothy B. Maddux writes: > >>I disagree with the statement that sets are caused >>in large part by wave-wave interference. Here in >>S.B. we get very even swell lines, with little chance For us it is a rare treat to see lines like these. Probably twice a year if we are lucky. {:^( > > >Good point. Here in North Cornwall, our swell window is fairly wide. >It's about 48 degrees to the South-West. Unfortunately the majority of >swell comes from the North-West, that's blocked by Ireland. The big >continental shelf (over 200 miles) doesn't help matters. The continental shelf does have a big effect, but that's another story. in fact a lot of the waves that we surf are generated in the "shallow water" over the shelf. >OK, back to the point. I kinda think you don't need multiple sources. >Going back to my sound wave analogy, think about strumming a chord on a >guitar. You've got six individual waves emanating from a single source. >Couldn't that happen with a storm at sea? Yes, it does, just like blowing on the water in a swimming pool a storm creates waves of all periods. Then as they propagate they spread out and sort out by 'dispersion'. This is the faster ones moving to the front. It is why we see the surf jump from small to huge in a matter of minutes, sometimes with each set bigger than the last one. In Cali they see this much more often than we do in EU, as the waves typically have travelled further and dispersed more. [This was covered extensively in "Left coast right coast" last summer. It is in my "Best of" archive.] As we tend to surf more locally generated swell we don't see it as often, unless you are looking really hard. Even a swell generated right on the far side of the Atlantic is only half the distance away from one generated on the far side of the Pacific from Tim and Tom! >Try generating some tones in Cool Edit (Shareware). Choose a Base sine >wave of, say 220Hz (choppy slop, eh?). Bang in 5 frequency components at >1.1, 1.2, 1.3, 1.4, and 1.5 times the freq. of the base wave. >Et voila, check the display. If properly cooked you should have a >repeating sequence of waves; 3 set waves interspersed with 12 smaller >waves. It has a nice warblie sound too! > >I kinda like the idea of the swell warbling to us, in a freqency so low, >we can ride it. The universe sings to us, we only need to learn to listen. {:^) Bobbing out there on the surf you can listen to the sound of storm half a world away, even to several at once. [Researchers at Plymouth Uni have measured the swell from storms in the South Atlantic!] The tides are the song that the sun and moon play on the ocean, and the shallow waters round us literally do cause harmonics to these frequencies. That's what causes it to flood faster than it ebbs, climaxing in the Bore. The atmosphere, lithosphere and magnetosphere experience the same tides. Several processes cause beautiful internal waves wich travel along sharp density gradients deep within the ocean in the same way as wind waves travel along the much sharper sea-air density gradient. Some of theses are also related to features that cause the sound channels within the ocean that allow pelagic mammals to communicate over vast distances. >Couldn't a weather system produce a bunch of waves at slightly different >frequencies. Oh! Hang on a minute! That was what you were saying a few >posts ago, wasn't it? Yup. >If this is all total bollocks, then tell me to shut up. It's not as if, >all this empirical reasoning is very scientific. You're the one with the >letters. I think that you are getting the picture now, or should I say tune? >I suppose, it's a question that doesn't really need answering anyway. The >waves will still keep coming in sets, whether we understand them or not. Their beauty is enhanced by understanding. Ric -BullShit (with Hons), MoreShit. Harwood. [can you tell that I want to come back as a whale...] Ric. -- EuroSurf forecasts: http://www.discoveryinternational.com/ric/surf.htm PGP public Key ID: 0766ABE5 From a.best@barnsley.ac.uk Fri Jan 17 13:03:09 1997 Newsgroups: alt.surfing Subject: Re: simple question From: fishy Date: Fri, 17 Jan 1997 12:03:09 +0000 John Webster wrote: > > I was jus' wondering: > > Why do the bigger waves come in sets? Seriously. I've been surfing for > about seven years now (with some landlocked periods) and I don't think > I've ever read or heard an explanation. Actually I don't think I ever > asked anyone before. > > I know bigger waves have longer periods, and I'm familiar with how the > wave forms in relation to depth, and concentration of energy as it > approaches shallow water, but sets? I know all about bigger sets first > hand, experientially, and resulting hold-downs, etc., but I don't know > why the waves come in sets. > > Why are the smaller waves and bigger waves organized in such a > semi-regular alternating fashion? Some bigger, then some smaller, > bigger, smaller. > > Thanks for any info. I won't sleep until a find an answer...I might > surf, tho. > > --John W. > johnw@cpg.com My very simple level of understanding on this issue of sets is that as as waves travels/passes energy on (as we all know that its not the water that moves but the molecules 'passing' on the energy to the next molecule)the leading wave 'looses' energy to such things as getting other molecules to start moving, wind and drag on the sea bottom and as a result of these forces acting against the leading wave it decreases in size. The wave behind takes up the struggle to reach land as such a tiering effect takes place This may be complete rubbish or contain a little bit of truth but either way it may get you some more acurate postings-- ________________________________________________________________ "This life of ours begins as a quest of the child for the man, and ends as a journey by the man to re-discover the child." - Laurens van der Post http://www.barnsley.ac.uk/~fishy _________________________________________________________________ From tbmaddux@alumnae.caltech.edu Fri Jan 17 19:18:53 1997 Newsgroups: alt.surfing Subject: Re: simple question From: tbmaddux@alumnae.caltech.edu (Timothy B. Maddux) Date: 17 Jan 1997 18:18:53 GMT In article <32DF6A7D.1290@barnsley.ac.uk>, fishy wrote: >... as a result of these forces acting against the leading >wave it decreases in size. The wave behind takes up the >struggle to reach land as such a tiering effect takes place... What fishy is referring to is a neat property that I alluded to in a sibling posting to this one. However, the grouping of waves is purely a consequence of the nature of the wave motion, and not caused by any sort of friction (it can be explained theoretically without the need for including frictional or viscous effects) or interaction with the bottom. The phase speed of waves is the speed at which the wave crests approach a stationary observer (like a buoy). Wave groups (see the sibling post) travel at a speed known as the 'group velocity'. This is the speed at which the energy of the waves propagates. In deep water, it is half the phase speed. So, if you were watching a group of waves move towards you on an otherwise totally flat ocean, you would see wave crests that appear at the back of the group, increase in size to the middle, and die out as they reach the front of the group. Again, the reason for this has nothing to do with friction or interaction with the bottom of the ocean. In fact, it is most noticeable in deep waters where the bottom is essentially nonexistent. I find this really fun to watch when our lab's wavemaker starts up and waves begin to move down the tank, only to disappear. -- .-``'. Timothy B. Maddux, Ocean Engineering Lab, UCSB .` .`~ http://www.engineering.ucsb.edu/~tbmaddux/ _.-' '._ "From the essence of pure stoke springs all creation." From gwarner@algonet.se Sun Jan 19 04:49:03 1997 To: "Timothy B. Maddux" Newsgroups: alt.surfing Subject: Re: simple question From: Gerrie Warner Date: Sat, 18 Jan 1997 19:49:03 -0800 > I find this really fun to watch when our lab's wavemaker starts > up and waves begin to move down the tank, only to disappear. > Hej so we know enough to make a few new breaks in S. Cal for example? What are we waiting for? From mickjevans@aol.com Fri Jan 17 23:13:15 1997 Newsgroups: alt.surfing Subject: Re: simple question From: mickjevans@aol.com (MickJEvans) Date: 17 Jan 1997 22:13:15 GMT >> Why do the bigger waves come in sets? Is it because there are different wave patterns approaching land at different intervals, and every now and then the patterns coincide and make big waves. It's either that or a ocean design parameter that allows us to paddle out between sets Mick Evans