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Hope this one hasn't been discussed...I'm in a bit of a hurry and wanted to post this before going to school. I was talking to a friend about the southern hemisphere, of which I know nothing, and mentioned the old factoid about the water in the toilets moving in the opposite direction of the water in the northern hemisphere. So, I googled something like "toilet Southern hemisphere" and found a lot of information on the Coriolis Effect. The effect can't occur over small areas, e.g., toilet bowls, but my question is what are the applications of where the effect actually does occur? Are there tornadoes in the southern hemisphere? Here's one pasting of something read last night:
Fred W. Decker, professor emeritus of oceanic and atmospheric science at Oregon State University notes, however, that the Coriolis effect may actually have little to do with the behavior of real-world sinks and tubs...
Just wondering,
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Dunno if it's YART or not, but I have more info than you'll EVER need on this one! Tornadoes and other such things (like ocean circulation) rotate one way in the NH (= oceanographer-ese for Northenr Hemisphere) and t'other way in the SH. Easy weather application: Wind blows counterclockwsie around a low pressure system in the NH.Take any weather map showing pressure contour lines, and look at it. A good first estimate of wind velocity and direction can be made by looking at the contour lines. The wind blows ALONG the contour lines (direction determined by whether you have a high or low pressure system) and the strength can be estimated by how close the contour lines are closer together (PM me for a formula if you REALLY want to know!). If the lines are very close together, you have a strong wind - farther apart, a weaker wind. Try it - find yourself a contour map of the atmospheric pressure in your part of the US right now and figure out which way the wind "should" be blowing (remember, CCW around low pressure and thus CW around high pressure) and then check the weather report to see if you're right! (There are other factors involved, especially geographic things like hills, mountains, etc., so it doesn't always work out perfectly.) Any SH readers should turn that around - it would be CW around a low-pressure system, and CCW around a high-pressure system. Anyway, like I said, ocean circulation follows the same sorts of rules. In oceanography (and presumably atmospheric science) we use "cyclonic" (= low-pressure in the centre) and "anticyclonic" (= high-pressure in the centre) to remove the hemispherical ambiguity. That is, if you know your physics, you can always figure out the actual direction if someone says "cyclone in the NH" for example. I like the quote in my oceanography book "However, the observer in the southern hemisphere is upside-down relative to the observer in the norther hemisphere and he calls the motion anticlockwise...It is a matter of point of view." 
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so sucks to you, Max, CapK, stales, and all the others
Not to mention that even tornadoes are small scale when viewed from the consideration of the Coriolis Effect.
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enthusiast
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Went to a party with old Coriolis and the outcome was that while I didn't drink anything I came out feeling dizzy. He has that effect on people. I think I was dizzy anti-clockwise. But then the old blowhard was always something of a spin doctor!
Heard tell of the Roaring Forties? Nice nightclub in rain-sodden downtown Okarito, population -2. Never really stops. Kinda blows you away, it really does.
The idiot also known as Capfka ...
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I'd like to apologize for posting "Coriolus Effect" on Q&A, but I didn't know where else to post it.
I'm trying to understand the meaning of the term, so I figured Q&A would be the place. Didn't think Miscellany would be it since it's not about coining or anything like that.
And it shurr didn't seem to be a place for Wordplay.
Without anywhere else to go, I figured, "To understand correct applications of the said effect, pose the question on Q&A."
Not meaning to rock the boat, clockwise or otherwise,
WordWind
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No worries my dear WordWind, we will make it into a word post yet! I have some favourite oceanography words which I've collected over the last couple of years. Just to be mean I will post them without definitions for now (I am supposed to be working after all) and you guys can all discuss them! Advect (or advection) Bathymetry Drogue Eddy Fetch Seiche Sill Swell Thermocline Turbid (or turbidity) Vorticity Doldrums Fjord TTFN!
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Another great ocean word, oft misunderstood, is (tada!):
Ground
And some others:
Surges
Tidal Waves
tsunami
Edited out the "s" and replaced with "n"--thanks, Faldage!
Riptide
Ebbtide
Surf
Tide pools
Undertow
Beached regards,
WordWave
PS: How do you spell "tsusami"? Can't figure it out. tsunami
...got it, Faldage!
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How do you spell "tsusami"? Can't figure it out.
With an n.
tsunami
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Some more shore words
Berms
estuary (estuaries)
barrier islands
barrier reefs
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Soomer eeza coomin' een,
Lovely seengs cuckoooooo...
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Soomer eeza coomin' een,
OK, you asked for it.
Sumer is ycomen in,
Lhude sing, cucu.
Groweth sed and bloweth med
And springth the wode nu.
Sing, cucu.
Awe bleteth after lomb,
Luth after calve cu,
Bullock sterteth, bucce verteth,
murie sing, cucu.
Cucu, cucu, wel singes thu cucu,
ne swike thu naver nu.
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Not "berm", I think, Helen. You see that word a bit in real-estate practice, as a berm running alongside the highway to buffer noise. But admittedly, I did not stop to LIU.
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You're right Helen.
berm (bûrm)
n.
A narrow ledge or shelf, as along the top or bottom of a slope.
Pennsylvania, Ohio, Indiana, & West Virginia. The shoulder of a road.
A raised bank or path, especially the bank of a canal opposite the towpath.
A terrace formed by wave action along the backshore of a beach.
A mound or bank of earth, used especially as a barrier or to provide insulation.
A ledge between the parapet and the moat in a fortification.
tr.v., bermed, berm·ing, berms.
To provide with a berm or berms.
[French berme, from Dutch berm, from Middle Dutch bærm, berme.]
--------------------------------------------------------------------------------
The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2000 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.
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It sounds like, as I thought, the word is not particularized to the context of "shore". Thanks for the LIU, mav. In flood-control practice (with which we who like in so flat and ill-drained a land as Chicago are familiar ), berms are often used in conjunction with "swales". Post-edit to dear-dear Dub-Dub : All I'm saying is -- well, let me analogize. You wouldn't put "bird" in a list of shore-words, even though of course some types of birds do make the shore their habitat. So too the six definitions of "berm": most (though not all) are unconnected with the shore.
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Mav pastes:
A terrace formed by wave action along the backshore of a beach.
...sounds like a shore term to me, Keiva... (You wrote: It sounds like, as I thought, the word is not particularized to the context of "shore". " Mebbe not limited to the shore, but certainly nothing short of the shore!
Beach regards,
WordWaves
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Thanks Mav, Long Island famous ocean shore (and yes, WO'N, NJ's too,) is made up of barrier island with berms on the back (bay side).. any construction that impacts the berms requires an enviromental impact statement and public hearings.. so i have gone to speak about Sound Berms! (talk about confusion!!-- a public meeting on Sound (LI Sound) Berm (construction impact) -- but they left out the Blue!)
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Meanwhile, the version I was most familiar with was that of barriers around gun emplacements from interest in the Napoleonic Wars I know, I know - I should get out more!
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Well, now I've got backshore, to go with all those foreshores I've been coming across. Still don't have a clear picture in my mind, being about 650 miles from the nearest coast, but that's ok.
Okay, Bean--for the edificatioin read: amusement of all, I am going to attempt to define your lovely list of oceanography words, which I thank you for posting.
Advect (or advection)--the direction of the current
Bathymetry--the depth of the troughs
Drogue--the pull of the tide going out
Eddy--I KNOW this one!--that little swirl
Fetch--no clue
Seiche--no clue
Sill--no clue--crest of a wave?
Swell--the water rising and falling
Thermocline--temperature variance
Turbid (or turbidity)--the movement of the waves
Vorticity--um--a circling current
Doldrums--near-flat water
Fjord--those things in Norway
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Seiche
We useta have these in Chicago when I was just a wee sprout. It's a small lake sized (not that Lake Michigan is a small lake) tsunami sort of thang, cept I don't think it was caused by seismic disturbances.
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Seiche
We still have 'em, Faladage. I've seen one about 5' one morning fishing with my brother. I heard there was a "wicked good" one about 20' tall sometime in the 50's. They are caused by a tight and fast moving High-meets-Low pressure system boundry that travels parallel to the shore line. The resulting reflecting wave generally dissipates, but that depends on how different the two systems were.
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Fetch--no clue
_____________
a fetch is a bit complicated to explain, but it's basically one side of a beat.
If you're going upwind in a yacht/sailing dinghy then you have to beat, which means going at roughly a 45 degree angle to either side of the wind as a boat with sails cannot go directly into the wind. This point of sail is as close to the wind as you can get and is called being 'close-hauled'. With me so far??
A beat is only a beat if you have to use both sides of the angle - ie zig-zagging (tacking) towards the wind to get from A to B.
If you can get from point A to point B without having to tack - that is staying on the same close-hauled course the entire way then you are fetching that point and are said to be on a fetch.
Once you are no longer close-hauled then you're not fetching any more, but veering towards a tight reach (some other time!)
Clear as mud - right??
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Yeahbut, Keiva, berm is clearly defined as a geographical feature of the shore. Birds aren't included as one of the definitions, so you at least can't say a bird is a berm--not that you were getting at that, but thought I'd throw it in!
If a berm's at the shore and caused by the ocean, then it belongs on the list the same way tide pools (that come and go and don't even have the staying power of berms) could be included. It shore sounded to me as though you were trying to say a berm ain't at the shore, though it clearly is according to the definition provided.
You wrote:
You wouldn't put "bird" in a list of shore-words, even though of course some types of birds do make the shore their habitat. So too the six definitions of "berm": most (though not all) are unconnected with the shore.
Sure, most aren't connected, but one of those rascally definitions is intimately connected with the ocean--owes its very existence to the ocean.
It's the ocean causing said berms that makes me think Helen's entry is a.o.k.
I'll add:
The Outer Banks, NC
...the ocean is gobbling them up with the help of hurricanes!
Beach regards,
Wordwind
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this one i know
Turbid (or turbidity) -- clarity of the water..
(ie, the normaly clear cool blue water of the tropical lagoon, was made turbid by the mud slides..
(forgetting the spelling of (lhora?)-- our geology thread word..)
Turbity is important-- it effects how deep sunlight can penitrate the water.. colder water, in general, is more turbid than warm water.(dark, opaque northern seas, clear, light tropical ones)
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and here one we have done before
a bore.. (a tidal bore)
rip tide
undertow i don't remember seeing it..
and little neck bay is home to a rare shore effect
mud volcanos.
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In the ocean near Montezuma, Costa Rica, I swam in waters that had a curious bubbly phenomenom, much like swimming in warm champagne. It made me giggle. Is there a name for this? Ok, then, an explanation?
Could it have something to do with volcanic activity? Waaaah. I want to go back!
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It shore sounded to me as though you were trying to say a berm ain't at the shore
Nice pun! If I were saying that, I'd be clearly wrong.
I'm jest sayin' that a berm "ain't necessarily at the shore" -- in fact, most berms aren't there. "Berms", under all but one of AHD's definitions, can be away from shore. (As you note in contrast, a tide pool is, of course, always by definition on the shore.)
To "shore up" our mutual wordplay, here are some "shore" words, new to me, that I stumbled upon. The "shore" is apparently divided into backshore and nearshore:
--backshore: The area of shore lying between the average high-tide mark and the vegetation, affected by waves only during severe storms.
--nearshore: The region of land extending from the backshore to the beginning of the offshore zone.
But it gets even more confusing. Since "nearshore" extends to the start of the "offshore zone", it seems to includes some land that is always submerged. That is, "nearshore" does not end at the water's edge:
--offshore (noun): The ... submerged land extending seaward from beyond the region where breakers form to the edge of the continental shelf.
--breaker zone:: The nearshore zone between the outermost breakers and the area of the wave uprush. Also called surf zone.
[all definitions per bartleby; emphases added]
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Curioser and curiouser. Berm seems to be one of those words differently defined (in this respect) in different dictionaries. AHD (which mav quoted above) includes one shore-related definition. But contrast Merriam Webster on-line:
berm: a narrow shelf, path, or ledge typically at the top or bottom of a slope; also : a mound or wall of earth
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musick, perhaps you can confirm this? I believe seiche is specific to a type of wave in a lake -- that is, you wouldn't have a seiche in the ocean.
I can't speak to the cause of a seiche, but I believe that one of its characteristics is that it oscillates back and forth across the lake.
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from Bean's great list -- fetch
I think an another meaning of fetch (beyond what rkay notes) was discussed in the novel The Perfect Storm. [Anyone have a copy handy?] As I recall, the fetch of a wind is the distance it travels over water: the longer the fetch, the larger the wave it will build up. For that reason, even the largest waves on lakes are nowhere near the size of major ocean waves.
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spring tide: When the sun, moon and earth are aligned. neap tide: When at right angles the forces are not aligned. The time between spring and neap is approximately 7 days. Here's a link to a Coastal Navigation site with a marvelous animated illustration, chart, and full tidal story: http://www.sailingissues.com/navcourse6.htmlFrom the site: The earth is also in orbit around the sun (one turn in one year) creating not only another centrifugal force but also a gravitational interaction. These two yield a bulge on the night site (centrifugal) and bulge on the day site (gravitational) both of them moving as the world turns. Therefore, a certain place on this world will experience two high and two low tides each day. With these forces alone, we would not have spring tides and neap tides. Spring tides have higher high tides and lower low tides whereas neap tides have lower high tides and higher low tides. Hence, the range (difference in water level between high and low tide) is much larger in a spring tide than in a low tide. The Only WO'N!
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tombolo:
A coastal feature that forms when a belt sand and/or gravel is deposited between an island and the mainland. This feature is above sea-level for most of the time.
swash:
A thin sheet of water that moves up the beach face after a wave of water breaks on the shore.
The Only WO'N!
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mav's berm: Merriam Webster on-line: berm: a narrow shelf, path, or ledge typically at the top or bottom of a slope; also : a mound or wall of earth
edit: you sneaky thang, DJ! - and you got me thinking with your 'missing link' that you were saying there's no such usage context...
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mav's bermMeanwhile, the version I was most familiar with was that of barriers around gun emplacements from interest in the Napoleonic Wars. I know, I know - I should get out more!Did ya click the photo link, mate? The Only WO'N!
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>Once you are no longer close-hauled then you're not fetching any more, but veering towards a tight reach (some other time!)rkay you cad!!! Who you calling unfetching and no longer close-hauled.  ____________________________________________ Jackie, I always thought a thermocline was not just a difference in temperature of the water but the visible line that is created where the different waters are separated. I find that the line is a lot easier to see in a lake where there is much less wave action than in the ocean. Most often the waters even have different clarities. __________________________________________ W'ON when did you stop being our Happy Epeolatrist? When did your epeolatricity start waning? Poor sweet thing.
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STOP!!!Well I read a entire book about berms. Remember about a hundred topics and five minutes ago yall were talking about berms? Berms are ,as defined by the people who study them, the strips of land that border the sides of a river or creek with topography and eco-systems directly interlinked to the effects of the stream. And doubledamn, I had something important to say about the "coriolis effect" but now I've forgotten it. Oh well... 
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the photo link, mate?yeah - thanks, very... Napoleonic Milum, isn't the main feature of <berminess> simply describing a bank or mound, and its specific context then determines what other features may apply? and tho' I don't get out enough and do read a *lot, I think I can proudly boast I haver *never read a complete book about berms 
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Nobody will probably believe this, but, honest to goodness, last night I dreamt I was trying to walk down a steep berm at the shore. Really. I think it must have been a precogniscient dream about today's AWAD berm talk. An aside about that dream, as I was trying to walk down the steep incline of this brown sand berm, I saw a huge dinosaur foot print in it...like that of a T-Rex.
Berm regards,
DreamDub
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edit: you sneaky thang, DJ! - and you got me thinking with your 'missing link' that you were saying there's no such usage context...Well, akshually® the first link wouldn't click off the cache, so I was off fishing for the page url when you popped in...very fortuitously, I might add. Couldn't've planned it better meself. And as far as the "Napoleanic" thing...well, I just went and found ya the biggest gun berm goin'... that one oughtta hold ya for awhile! W'ON when did you stop being our Happy Epeolatrist? When did your epeolatricity start waning? Poor sweet thing.Waning, my dear Bel? Never! Rather gaining in epeolatricity, fueled, of course, by the legendary and envigorating exploits of Don WO'N!...the only WO'N!  hey, watch it, mav, I heard that!The Only WO'N!
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Then, of course, there's that whole country of berms...Berma. Myanmar
The Only WO'N!
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When the waves hit the berm and slice it even more, could you call it a Berma Shave? Anybody remember those ads?
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one about 20' tall sometime in the 50's
That must of was the one that stuck the word in my retrievable memory bank. Any idea what causes them? That's the part that escapes me.
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Re:Burma Shave Ads? Any idea what causes them?
Ad men.
Berm can be man made as has been pointed out.. they sometimes run along hiways, and act as sound barriers, or as Mav pointed out are used for defences.
Shore berm are natural creations of sand, wave and wind. and they are defence barriers. they are the backbones, as it were, of barrier island, and barrier islands protect the main portion of the shore line.
Flood devistate places like the hamptons and wildwood, but rarely the main portion of Long Island or NJ. Berms, 10 to 20 feet higher that normal high tide, they are protections against storm surges too.
A storm doesn't actually have to come on shore to do damage. a big storm at sea, with strong winds, can push water, the way a push broom might. when combined with high tides, you can have a wall of water, not a tidal wave, but a slow, relentless surge of water.. berms help limit the damage the surge can do.
While we have our feet wet.. can some one explain to me again, (i promise this time i'll master it!) the rule of 12?
it is about the normal volume of water that moves with each hour of a tide.. when i first heard it, i final understood why sailors in days past, "sailed with the tide".
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Any idea what causes them [seiches]? That's the part that escapes me.You got me interested, faldage, and you'll find in the links below what is summarized here. Waves (however they are caused initially) may happen to occur with a time-period, between them, that matches the natural resonant frequency of the lake or harbor. In that case the successive waves (including the waves "rebounding" from the shore) will reinforce each other, building higher; the result is called a seiche. Its defining characteristic is thus not what has caused the initial waves, but the fact that they have "piled up". Every enclosed body of water has a number of natural resonances. If you sit in a bathtub part full of water and rock back and forth you'll find that at the right period (about a second) you can easily get the waves to grow until they overflow the bath. The resonant oscillation of the water is a seiche.Swiss seismologist F.A. Forel brought the word (pronounced "sigh-shh") into science in 1890. However, it seems the word was commonly used in German-speaking Switzerland to mean oscillations in alpine lakes. A tsunami is a wave caused by underwater seismic activity, such as an earthquake or and erupting volcano. A tsunami can be massive and, if it hits the shore, incredibly destructive. http://www.soest.hawaii.edu/GG/ASK/seiche.htmlhttp://oceanworld.tamu.edu/text/students/waves/waves1.htm, and continue to successive pages. http://www.weathernotebook.org/transcripts/2001/04/18.html
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At Planning Boards here in the NorthEast, sidewalks which have been built in the last ten-or-so years all are all required to have a sort of slope, or ramp, every so many feet and at intersections to facilitate wheelchair use. We call 'em berms!
What you all call Coriolis Effect I was introduced to as Coriolis Force! The late, great, Love of My Life explained it to me and since then when all the forces of the world seem aligned against me .... I blame the Coriolus Force (or perhaps now, the Coriolis Effect!) Like when posts go wide for no reason, the board is slow, the dog is driving me crazy, my hair is growing in crooked, my teeth itch, etc., etc.
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An on-the-spot news account of this Chicago seiche: http://www.kacm.com/Tidalwave.htmInformation picked up from various sites: Large seiches are particularly dangerous because they hit suddenly and without warning. This seiche was about 10 feet [3 meters] high (about the maximum on Chicago's lake), and was quick: at one location "the water surged more than 10 feet within a few minutes."
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Keiva, Please allow me to explain the events of the 1954 rouge seiche event that claimed the lives of ten Chicagoans.
A storm passed through Chicago and then moved on across lake Michigan.
Lakes, like bowls, slosh. The 55 mile-per-hour winds pushed the water to very high slosh hights to the northeast of the Lake Michigan bowl, and then, on the slosh back, the ten foot waves, killed the ten Chicagoans.
This event was cited in the book "EL NINO" as an effect of wave build up that can also be applied even unto the twelve thousand mile bowl that is the Pacific Sea.
The Coriolis Effect modifies the sloshing, as I will later explain to those who haven't read the book.
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Saw "White Squall" yesterday--$.99 rental and the best bargain I've seen in a long time.
When the skipper is being tried for lack of judgment, either a witness or an attorney argues that the white squall's existence at all is probably apocryphal--something not proven to be a natural phenomenon. Does anyone know anything more about this?
The way the filmmakers showed the white squall was as a sort of huge, white rising wave of a curtain of madly falling water--it looked like a waterfall hitting the ship.
Something else that was explained that was news to me was the definition of a loose cannon--there was a boy who was causing trouble and the term was being implicitly applied to him. Anyway, here's what the skipper said about the loose cannon:
"You know what a loose cannon is? A couple of thousand pounds of pigiron crashing around on deck"...putting holes into everything.
The boy who records the story, when they arrive at the Galapagos Islands, I believe, says they "saw the bliss of nature in the absence of man," which was the single best contemporary comment made in the story. I use "contemporary" here because Shakespeare, Donne and other classic writers are also quoted throughout by an English teacher.
Finally, there's a shot of the ship going under--she appears to be completely submerged--but then she rolls back up out of the ocean.
Anyway, if you missed this one, it's worth taking a look at. I cried at the end--so, if you like tearjerkers and are sensitive, you may shed a little tear.
Best regards,
DubDub
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Well, I got a degree in the subject in 1980 but the old brain's a bit foggy these days...
To be frank Bean is the best qualified - doing her PhD in oceanography. I hear she's a bit busy at the moment so that's maybe why she hasn't chimed in to set us all straight.....
In her absence, I think Keiva and of troy make pretty good stand in oceanographers.... Both sorted out the matters of fetch and berms pretty well I thought. Fetch (the distance the prevailing wind travels over water) is one of the components that contributes to wave height - along with a few others that I've forgotten - but which include the depth of the water and the slope of the coast as I recall.
The sill depth is (I think) the depth to the continental shelf (help Bean!)
Noone seems to have mentioned cusps yet. These are the seaward pointing "horns" at each end of a berm - they point to where the rips are generally operating offshore. Both are features of a beach's winter profile - more wave activity in winter, steeper beaches, greater cusp and berm development.
Keiva was also correct to push for berm being a generic term, not necessarily for exclusive maritime use. Frinstance, there are berms in open pit mines. In this context however, their counterparts are not cusps but batters. The batters are the steep parts of the pit wall that link a series of horizontal batters.
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Thank you, milum. Fascinating! I now know what I'm going to be doing all this afternoon.
[rushing off to find that book -e]
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Making an educated guess.......
Im guessing we were talking warm waters?
If so, then I think we're onto something - gases dissolve more easily in warmer water. A change in atmospheric pressure (from high/er to low/er) could theoretically result in the phenomenon you mention. Just as when you open a bottle of soda, the bubbles come out.
If so, I'm betting it was carbon dioxide (just like soda and champagne) - particularly as you didn't mention whether there was a smell present.
CO2 (or any of several other gases) is given off by volcanic action as well, so it may have been a crustal source of gas bubbling up through the ocean.
A last guess is that it may have been oxygen being given off from an unusually high concentration of algae.....
(I can't sign off without asking whether you and your bathing colleagues had previously eaten a few batches of spicey Costa Rican food?? There again, you didn't mention any smell did you....)
Thanks for bringing it to our attention.
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(I can't sign off without asking whether you and your bathing colleagues had previously eaten a few batches of spicey Costa Rican food?? There again, you didn't mention any smell did you....)
Well, of course we were eating spicy food, but, that t'wernt it. No smell. TINY bubbles! Montezuma is at the southernmost tip of the Nicoya penninsula, Pacific side of Costa Rica. There are several seperate beaches, Montezuma beach, Sano Banano beach, Red Rock Beach, Long beach(that of the bubbles) and the Black Sand beach. It is my understanding that the Nicoya penninsula was formed by a lava floe. My guess is there is some type of gas (prolly CO2) escaping through the sand in that one area that causes the bubbles. I just wanted to know if any of youse guys that actually know about these things might agree with my theory. (still looking for the perfect pic link but have to leave for pottery. This spot saved)
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WW:
Having spent some time in the sH, and having lived in the NH the rest of my life, I can double damned assure you that the water in the toilets in the Southern Hemisphere goes the same way as does the water in the Northern Hemisphere: down.
TEd --flush with victory for having been the only one to get it right!
TEd
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DOWN UNDER: SOLVEDIt's a well know fact that we's mates from down under make up seven per cent of the world's population, and yet raise thirty-eight per cent of the world's cain. One such cain they raise is that it is we, not they, who live near the bottom of the earth. Ha ha ha. This morning I devised a simple experiment that you can do at home that proves... (a) Einstein was right about relativity. (b) The duel nature of the coriolis force. [c] That Aussies and Zealies live down under. OK, Everybody ready? OK, Now stand up and... 1)Raise your right hand towards the ceiling. 2)Now with your arm fully extended point your index finger back towards the top of your head. 3)Now start rotating your finger in a counter-clockwise circle. 4)Slowly rotate your helicopter finger down the front of your body down to your crotch. 5)Now say... "Tan me hide, Mate, when me blooming 'copter passes me equator belt and gets to me bottom, it changes direction and circles clockwise! Ha ha ha. Boil me in Kangaroo oil, We live in a land down under after all."
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Ha ha ha. Boil me in Kangaroo oil, We live in a land down under after all."
Is the operative word here "live"?
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While we have our feet wet.. can some one explain to me again, (i promise this time i'll master it!) the rule of 12?
_______________________________________________
It is indeed all about the volume of water that flows between tides.
Basically, you have six hours between high and low tide (or between low and high tide whichever way you look at it).
In the first hour 1/12 of the total volume of water that's going to flow in/out will flow.
In the second it will be 2/12
In the third, 3/12
In the fourth, 3/12
In the fifth, 2/12
In the sixth, 1/12
So the flow of the tide is always fastest in the middle two hours of the cycle because that's when the biggest volume of water is travelling.
That pretty much applies wherever you are in the world, unless you're somewhere like Poole Harbour which has really unusual tides because it has two highs and two lows in each cycle instead of just one, but that gets really complicated!
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explain ... the rule of 12?
Well, it's sinusoidal, innit?
Think of a point on a circle, moving around the circle at a constant speed. Now think of looking at that circle from one side. The circle will appear as a line and the apparent speed of the point is going to be slow when it's near the ends of the line and fast when it's near the center.
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...apparent [E.A.] speed of the point is going to be slow when it's near the ends of the line and fast when it's near the center.Actually® anyone who's ever played in a marching band or danced with the Rockettes will tell you the speed differences are much more than merely apparent, being faster on the outside and slower as you near the center. But are we talking apples and oranges here?
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The linear speed will be greater the farther from the center the trombone player is, assuming the same angular velocity (i.e., speed measured in degrees per second). The center I referred to above was an apparent center of a line segment formed by the one-space projection of the circle on the (e.g.) y-axis, no point of which would correspond to any point on the circle closer to the center of the circle, of which they ain't none anyway being how as all points on a circle are equidistant from the center.
If you can't lure them with logic, baffle them with bullshit
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Yes, a marching band, or the wheels on a truck have a differencial.. (by an large, trains don't, so curve on trains are much wider and rounder than curves on roads.. but there are other differences as well..)
a differencial gear (actually several gears,) allows the inner wheel to turn slower than the outer wheel.. In marching bands, the rows on the inside of the turn take smaller steps, and the rows bunch up a bit.. the marchers on the out side of the turn take larger steps, and the rows splay out slightly.
but i hadn't thought of the tide working the same way--
especially because High tide in lower manhattan come at a different time that high tide in greenwich CT, about 25 miles away.. (something else i have never quite understood)
i guess its sort of like a wave in a stadium.. High tide is standing, low tide is sittting, and high tide moves..but looking at the local tide tables, its doesn't make too much sense..
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Well, it's sinusoidal, innit?The height of the water is, yes, but to figure out the speed of the tide you have to take the derivative of the sin curve, which happens to be the cosin curve. Where the sin curve crosses the x-axis (halfway between it's highs and lows) the cosin curve reaches it's maximums and minimums, meaning that the speed of the tide will be greatest in the middle. I hope that was clear. 
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tidesWhat Faldage just discussed and more is all right here, rkay...including an animated figure and charts. A complete study of tidal cause and affect. http://www.sailingissues.com/navcourse6.htmlThe Only WO'N!
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Per our beloved belM: thermocline was not just a difference in temperature of the water but the visible line that is created where the different waters are separated.
I find that the line is a lot easier to see in a lake where there is much less wave action than in the ocean. Most often the waters even have different clarities.
This line isn't always visible, but it is the line that divides a mass of water of one temperature from a mass of water of higher or lower temperature. My experience with it is from diving - typically when you're in the water the thermocline isn't visible, but sometimes you can really tell when you cross it - get 30 or 40 feet down and bbrrrrr!!!
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Found this online about the white squall (myth or not): The white squall may be myth, or it may be a microburst. If they form during daylight you might see the approach as a line of broken water or whitecaps rushing at your vessel, but usually they appear out of nowhere.
"The Pride Of Baltimore, a fine 137 foot schooner, was reportedly struck by a white squall. The 121-ton vessel sank about 240 miles north of Puerto Rico, casting the surviving crew members adrift for five days. The Toro, a Norwegian freighter picked them up at 2:30 a.m. May 19th, 1986.
"Here is an eyewitness account of the sinking: ‘A tremendous whistling sound suddenly roared through the rigging and a wall of wind hit us in the back. The Pride heeled over in a matter of seconds. The 70-knot wind pushed a 20 foot high wall of water into the starboard side. She sank in minutes.’"
A USATODAY.com graphic shows what a microburst is. While the graphic shows what a microburst can do to an airplane that’s taking off or landing and much of the research into microbursts was prompted by the danger to aviation, microbursts have caused other kinds of damage on the ground and I know of at least one case in which a microburst overturned a boat, killing 11 people. http://www.usatoday.com/weather/askjack/waoceans.htm...interesting to read there about the "microbursts." Also read several pro and con movie reviews of this film. Yeah, there are problems, but the shots of the ship in the sea are terrific.
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I only use this line for effect, but my parents used it, often..
Worse things happen at sea
with WWII not to far behind them, i guess for them, no matter what the peril, nothing was as bad as what could happen at sea.
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I once witnessed something akin to a white squall. I was working in a small restaurant facing East Grand Traverse Bay when a huge wind (microburst?) caused several birches across the street on the water's edge to topple. Looking across the bay, I saw a wall of white and nothing else. The whole thing lasted only 15 to 20 minutes, but when it was over, several boaters had lost their lives. My daughter and her girlfriend had barely made it to the friend's house to shut the windows when it hit. They were two terrified young girls, I can assure you. The friend's house was in a wooded area on the shore of the same bay. The boaters were lost in West Grand Traverse Bay on the other side of Old Mission Penninsula.
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OK, sorry to be away for so long, but I've been out with a cold. Here are some definitions from my list, you guys already got some of them yourselves, of course - what else would I expect from such a group? Advect - (verb) to be "dragged along" with the current. Little oceanic suspended things, like plankton, are advected - they move where the current goes - they can't swim of their own accord. Velocity can also be advected. (Now try and wrap your minds around THAT - I'm still not pleased with it myself!) The noun is "advection". Bathymetry - this one was right - the measurement of ocean depth and ocean "features" (rifts and ridges and stuff) Drogue - dammit, I have to look this up at school since this list had been compiled ages ago - It's a parachute-like thingy that is dragged along with the current and served some purpose in old-style current measuring instruments Eddy - Jackie is right, swirly things. Specifically, eddies are called "mesoscale" features because they're neither tiny like surface waves nor "basin-scale" like the Gulf Stream. Usually about 100-600 km in diameter, they're self-contained swirly bits of ocean, extending to great depths (i. e. not just surface features). Fetch - stales got this one (of course), the distance of open water across which wind blows, which affects the size of surface waves (bonus points for stales because he got that part, too) Seiche - we pronounce this "SAYsh" - you guys collectively got this one, it's like a bathtub wave. It's a resonant wave in an enclosed area, like a harbour. It can have a number of causes but the net result is some pretty amazing changes in water level. My prof has some great photos of a seiche a few years ago in Petty Harbour, which also affected St. John's harbour, and by sheer luck the associated flow anomaly was measured by some ADCPs (Acoustic Doppler Current Profilers) moored in St. John's harbour. Sill - this is a ledge of shallower water, for example, again in St. John's harbour, there is a sill. The harbour is about 30 m deep in the main part, but at the mouth of the harbour (the Narrows) there is a big ledge, where the depth is only 10 m or so. This has ramifications on how often the water "trapped" inside the harbour (in the part deeper than the sill) is flushed out into the sea. Swell - this is specifically surface waves generated elsewhere, which will be obvious because they don't go in the same direction as the prevailing wind where you are observing them. They are easy to observe as the slow up-and-down of the water. If you pay attention you'll realize most of the time they are not going the same direction as the local wind. This means they were caused by a storm somewhere else, and have taken a fair bit of time to travel to where you are. Thermocline - this one's been covered pretty well - it's the region of the sharp change in temperature that separates the upper ocean layers from the deep ocean. Typically this is at 200 m depth. The layer above the thermocline is well-mixed by surface winds but the layer below is unaffected by winds. Turbidity - helen (I think it was her) got this one right one - no need to add to it. Vorticity - the tendency of a fluid to move in a circle. It has a mathematical definition, too. It has important consequences for when eddies move into water of different depths, for example. Doldrums - the region near the equator where winds are generally calm. There are oceanic/atmospheric reasons for this which I can't recall at the moment. Something to do with atmospheric cells (and of course Coriolis forces!) Fjord - I'm sure most of us know this one but the word has a great ring to it - those steep ocean inlets like in Norway - and Newfoundland, and Labrador! Designed by Slartibartfast, I believe.
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Dear Bean,
Thanks for those definitions--clearly written and easy to understand!
You wrote:
Advect - (verb) to be "dragged along" with the current. Little oceanic suspended things, like plankton, are advected - they move where the current goes - they can't swim of their own accord. Velocity can also be advected. (Now try and wrap your minds around THAT - I'm still not pleased with it myself!) The noun is "advection".
...When velocity is advected, is it anything like the draft effect in racing? Seriously. Is it akin to two forces enhancing each other's force once they work in tendem?
Curious,
WW
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Re:Fjord - I'm sure most of us know this one but the word has a great ring to it - those steep ocean inlets like in Norway - and Newfoundland, and Labrador!
Ahem, cough, cough, NY's Hudson river is the souther most fjord in north america. the harbor is silting up rapidly, and turn the harbor into an estuary-- but it is still technocally a fjord.
a fjord is a sunken river, into which the sea has pushed..
in NY, salt water can be detected all the way up to poughkeepsie, 60 some odd miles up river..
the river is (stacked?) the fresh water floats on top of the denser salt water-- something like the thermocline--only its a salt/fresh water change.. (with brackish water too)
even a casual visiter can experience the same effect we all associate with fjords.. steep cliff, narrow or almost no river bank, in Manhattan.. the Metpolitan museums Cloisters in upper manhattan are a prime place to see the steep cliffs that bank the hudson. 20 or 30 miles upriver, at bear mountain,Hi Rubrick!, the river is narrow, runs fast and is over 265 feet deep! that is one sunken river!
It no wonder hudson thought he had found the great north west passage! I'll look for some photos of hudson from the cloisters.. but if you ever say the movie, "looking for Richard"-- you have seen them. most of the locations shots where in NYC, and several were in the cloisters.
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The whole thing lasted only 15 to 20 minutes, but when it was over, several boaters had lost their lives.-consuelo
In 1978 I was in a microburst. We were changing clothes to visit Beech Spring Cave near Lake Guntersville on the Tennessee River when -in a sudden- violent winds and torrential rains hit. The six of us sought refuge in a big Dodge van that rocked with alarming portent of overturning.
The deluge passed in about 15 minutes. But strong gusts of winds keep us imprisoned for 15 more.
To lighten the atmosphere as we waited out the tail of the storm, I offered Caver Tom ten dollars to eat the one inch long green horse-fly buzzing in a bottle who had been deftly caught by my son Danny as we waited. Tom is the quintessenial retro-woodsman. He walks through the woodlands as others would vist the salad bar at Denny's Restaurant. But the horse-fly was exceptionally ugly and Tom hesitated. Soon, though, the ante was raised to 40 Dollars. Our guests from out-of-town had never seen anybody eat a horse-fly before.
Tom ate the horse-fly, which became the hit amusement of the trip. The wind stopped and we had a pleasant visit to the cave, then we returned to Birmingham.
The next morning the headlines of the Birmingham News reported that 21 people had drowned when a freak microburst had overturned an excursion houseboat out of Huntsville. This was the worst maritime disaster in Alabama since the days of the Steamboats. The ill-fated sight-seeing boat overturned about the same time and less than a quarter of a mile from our van where Tom ate the horse-fly.
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a fjord is a sunken river, into which the sea has pushed
Guided only by hazy memories of old geography lessons, isn't it typically a coastal feature created by the flooding of an ice-formed 'river' valley?
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Heh, Mav! Just a heads-up ('cause I done gone and done the same durn thing too many time):
You jes' responded to the fjord stuff on the white squalls tuft of the thread. Me thinks that's what all the folks be talkin' about when they say we screw up the threads for those folks what's read 'em different than us! (Me, it done take me six months to finally unnerstan' what all this fussin' done been about!)
And to milum:
Thanks to you fer one heckuva story--that poor leetle horsefly must've felt he been caught in the jaws of a macrospout, huh? What yer Danny think of his specimen bein' et?
Best regards,
DubDub
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the river is (stacked?) the fresh water floats on top of the denser salt wate
Another great oceanography word - I'm getting the feeling you're thinking of stratified. (My brain is still fuzzy from the cold meds and I had to think for a while on that one!)
Both temperature and salinity (the salt content of the water) affect the density of the water - and that affects which water mass will be on top. Estuarine circulation describes what happens when a river empties fresh water into a salt water estuary. Basically what happens is that the fresh water "waters down" the salt water near the surface (this watering down is called entrainment, another great word). Then that whole, larger mass of lighter, less dense "fresher" water will leave the estuary on the surface. But because of conservation of mass, there will have to be an inflow near the bottom of the estuary - otherwise the estuary would drain! So you actually have an outflow of less dense water, and to balance that, an inflow of denser water. The key thing is that the volume of the outflow from the estuary is much greater than the volume of water that the river puts in, because of the entrainment.
There is also (surprise, surprise) inverse estuarine circulation, which happens when the river outflow is more dense than the water already in the estuary (this can happen with certain combinations of temperature and salinity of both waters - the most common example is the Mediterranean water entering the Atlantic Ocean). Then the river water sinks and flows along the bottom, and the inflow is on the top.
The characteristics of the Mediterranean outflow were useful during WW II. Apparently the submarine captains had to be aware of the flow in and out of the Mediterranean and they'd go to the depth where the water was going in the direction they planned to go, then cut the engines and let the current take them (so as not to be detected). Or something like that. (Anyone out there care to confirm or deny this one?)
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The problem with tides is that they are greatly affected by local bathymetry and are not usually perfecty sinusoidal. More great words: most regions have either diurnal (daily) or semi-diurnal (twice-daily) tides. Oh, it gets even worse! Usually, if you are in a place with semi-diurnal tides, one high tide is higher than the other, and one low tide is lower than the other! So you get: high high water, low high water, high low water, and low low water. ARGH!!!!!!
When we were on the Fraser River in BC last summer for a field trip, we were a good 100 km inland on the river, but the river is so huge that we still observe tides there. They were NOT sinusoidal. (Of course, thanks to Fourier, we know we can always represent them as sums of sinusoidal components - but that's another story!) They consisted of a sharp rise to high water and a slow drop to low water. The river nearly ground to a halt just before high water - compared with a speed of about 1m/s when the tide was going out. It was quite something to observe!
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When velocity is advected, is it anything like the draft effect in racing
Like I said, I'm not too fond of this idea myself. Imagine yourself observing a particular point in the ocean. You're trying to describe mathematically the changes in water velocity around you. A number of forces are at work. There's the pressure force, shear and stress forces, good ol' Coriolis...all those forces cause the velocity of the fluid around you to change. Now remember, for example, the eddies I mentioned above. They're localized "swirly bits" of ocean, and they can move around (kind of like a tornado but much less dramatic). If one moves toward you, it will bring along with it the velocity of the fluid in it. So the water where you're observing will suffer a change in velocity that's not due to any of the other forces I just mentioned, but just velocity that was "dragged in" from somewhere else. And a change in velocity is called acceleration. (Furthermore, wherever the eddy came from will have had velocity advected away from it.) So that's what I take to mean "advection of velocity". In our fluid equation there are, of course, mathematical terms to describe it!
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>>isn't it typically a coastal feature created by the flooding of an ice-formed 'river' valley?
Yeah, but crossing thread, i did mention NY is at the southern boundry for the last Glacier-- (glacier=Ice)--(the bit about the terminal moraine..) an yes, it was the last glacier, in the last ice age that scoured out the river bed..
the glaciers went further south inland.. but here on the east coast, NY markes the southermost extention of the ice covering, and as result, is home to the southern most fjord in North America. (i think there are even more southerly ones on the east coast of asia, either on island or mainland, but hey, that's not were i hang my hat, so i don't know the details!)
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Yeahbut© they're close enough that sinusoidal is a half decent first order approximation and it explains the phenomenon that rkay asked about.
If you want to get complex about it, the driving forces are two sine wave shaped forces of slightly different frequency and vastly different amplitude. Resistance and impedance are local variables but the whole thang could be modeled quite easily on an analog computer, at least to a second or third order approximation.
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Actually, Faldage, my book lists something like 12 different components of tidal periods. (There are irregularities in planetary orbits and also the effects of the other planets which are small but affect things in the long run.) And I understand that the way they do tide charts these days isn't from modelling, but from harmonic analysis. Rather than trying to explain why the components observed dominate in one particular place, they just observe it and extend the observations into predictions.
Back to the Fraser River example...my supervisor says someone tried to model that particular location but he doesn't think they got as far inland as we were...sometimes there's a lack of data...so I guess to some extent there's not much use in modelling when you can just use harmonic analysis and build the tide table quite easily. The guys who drive the tugboats probably don't care about the why of the tide so much as the when and where of it!
I had some nifty plots of not-very-sinusoidal looking tidal patterns in my book but I'm at home sick again (I made it into school this morning and gave up after a couple of hours) and can't scan them for you.
Edit: I've given it some thought and I do agree with Faldage: the tide you observe from day-to-day seems sinusoidal - but the overall picture, observed over many days, or a month, is not just a plain old sine curve, or even a superposition of just two frequency components, but much more complicated than that.
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> a fjord is a sunken river, into which the sea has pushed..
So is a ria.
Close to home for you Hev - the Hawkesbury/Nepean system ocupies a ria - a drowned river valley.
stales
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In reply to:
Tornadoes and other such things (like ocean circulation) rotate one way in the NH (= oceanographer-ese for Northenr Hemisphere) and t'other way in the SH. Easy weather application: Wind blows counterclockwsie around a low pressure system in the NH
Umm, what happens for us more-or-less equatorial types?
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what happens for us more-or-less equatorial types?
Well, the strength of the Coriolis effect depends on latitude, starting with zero Coriolis effect at the equator and reaching its maximum at the poles. Probably, in terms of large features like atmospheric pressure systems, this means the circular shape isn't very circular when the feature is near the equator. (This is party the reason for the doldrums near the equator, I believe.) As for tornadoes - I really don't know. I don't think they're able to form as easily at the equator since they are offspring of a pressure system. And they also don't travel very far (in global terms). I will see if I can find more info and PM you with it.
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I have noticed that Java doesn't seem to go in for wind much. A good stiff breeze before a major rainstorm but that's about it. Having said that, we did get quite a gale a couple of weeks ago with branches coming off trees and so on, but it's the first one I remember in coming up to 15 years here.
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Today's Chicago Tribune newspaper, on how are city fathers inflated the amount of parkland they supposedly will create under a controversial project:
When City of Chicago officials heralded the 19 acres of parkland to be creating ..., they were craftily including landscaped medians, sloped berms next to a garage and any patch of grass they could find. "A berm can have plants on it, and isn't that part of a park?" one of the project's architects reasoned.
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"A berm can have plants on it, and isn't that part of a park?" one of the project's architects reasoned
This is the same mind-set that decided catsup is a vegetable when served at a school lunchroom!
Sheeeeesh!
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... are what I get during allergy season.
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Yeahbut(r) that still doesn't explain the Poole Harbour phenomenen.
As I understand it, semi-diurnal means that you get the high high water, low high water, high low water, and low low water across the course of the tidal day (ie 24 hours ish). In Poole Harbour you still get the twice daily high tide eg at 7.00am and 7.00pm (approximate), but in each 12 hour period you will have 1st high, 1st low, 2nd high, 2nd low. The 2nd is high is your main high water. Basically, it comes in a bit, goes out a bit, comes in all the way and then goes out all the way, completely throwing out any rule of twelves! So, what would that be? Or is it just that all the curves and technicalities are getting me confused?
As far as I'm concerned, as long as I know what times they are, where and when the flow is strongest and which direction they're going in relative to my course so that I can make sure that I use them to maximum effect, I'm happy!
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the Poole Harbour phenomenon
If you dump a sinusoidal driving force into a chamber that has a natural resonance twice the frequency of the driving force it will oscillate at the higher frequency. Perhaps it is something like this that is happening. Where is this Poole Harbour, how big is it and how open?
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Poole Harbour:
http://makeashorterlink.com/?E1EA321C
It's a large natural harbour with a very small entrance. I seem to remember back in the mists of time that it's something like the 2nd or 3rd biggest natural harbour in the world.
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Love the map site. On second thought, I'd think that this was a pretty small body of water to have a natural frequency of twice a day. Bean? You're the most likely to have anything intelligent to say on this. Any ideas?
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Only just looked at this thread, golly gosh it is interesting! I am not a sailor or an expert, but I know that the double tide effect operates in the Solent and in Southampton Water. If you zoom out on the map of Poole Harbour you will see where these features are. I have understood that this occurs because as the water rises for high tide in the English Channel it does so first at the western end of the Channel and then gets progressively later as you move eastward up the Channel, so you get a high tide pushing into the Solent from the west as the tidal effect passes the western arm and then a second body of water from the east as it passes the eastern arm. If this is truly the cause of the double tide, however, I am surprised that it impacts on Poole harbour, and there may some other reason. When I was a very junior Civil Engineer, more years ago than...., I worked on a project to extend the capability of Poole sewage works. Up to that point they were discharging macerated sewage out to sea. If there were double tides.... well it doesn't bear thinking about really does it... dxb
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it does so first at the western end of the Channel and then gets progressively later as you move eastward
Now I'm confused. I know, I know. I'm often confused.
Shouldn't the tide move from east to west?
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Dear Faldage,
Well....yeah, I guess you're right, I didn't make a considered choice of direction there, I subconsiously assumed that because the Channel, the North Sea and the Baltic are just a little adjunct off the Atlantic, they would be fed from the European Atlantic coast tide. I am happy to accept that the effect works east to west, but the double tide is still the result - if the reason I was given is correct. I will try and check on which way the tide moves in the Channel - as said I am not an expert, or even knowledgable, on the theory!
dxb
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they would be fed from the European Atlantic coast tide
That's an interesting point. I hadn't thought of that. We already know that local effects can have huge overriding consequences. All this stuff is very impotant to me in my long term goal of unsuccessfully understanding the universe.
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my long term goal of unsuccessfully understanding the universe
A most optimitic goal. It's difficult enough to meet the goal of unsuccessfully understanding the universe.
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OK, sorry to take a while to reply. Some thoughts on tides and resonance: Yes, harbours that are enclosed can have a resonant frequency, and I'm sure that can modify the tidal dynamics. There's a formula to work that out, what I need is the length and width of the harbour. It might be tricky because it's a really funny shape which doesn't even approximate a rectangle. Give me some time on that one. (I don't feel like solving the differential equations again when I know the info is in a book on my desk at the university!) Regarding direction of the tide: Tides are actually very long-wavelength waves known as Kelvin waves. They travel with the coast on their right in the NH (which means on the left in the SH). Looks like this one should be travelling East to West. The best I can do on short notice for St. John's Harbour (which is practically rectangular and I just marked an assignment where the students figured out the period of one of the modes of vibration), much more so than Poole Harbour) is http://makeashorterlink.com/?H2F7213C, if anyone's interested. Here's a much better map, courtesy of the Port Authority: http://www.sjpa.com/images/Facilities/HarMap1.jpg
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Speaking of harbors.. here is a boat trip round NY upper harbor.. the slide show is about 350 slides, it covers about 10 hours.. of a commercial tourist attraction ride around Manhattan island. the url is to a home page, with a live web cam, or click on link to take the virtual tour.http://www.earthcam.com/usa/newyork/circleline/
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Well, this thread is ready to go on out to sea, and I've found a lovely ocean word I don't believe we have here:
spendrift
It's defined in Random House Word Menu:
spray swept by wind from waves during storm at sea...
and then an equally lovely term is given as a synonym:
spoondrift
...I can go to sleep on those two words, stormy though they may be. What do you call a word that sounds as though its one thing (e.g., spendrift and spoondrift sound laidback and easy), but is actually quite something else? Spoondrift just doesn't sound stormy at all to my ear.
Beach regards,
WordWave
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Dear faldage, High Tides along the south coast of the UK:This is all strictly non-technical and whether it will assist you in universal understanding I hesitate to predict! I don't think it helped me much - knowledge is one thing, understanding another. What I am told and what I read do not seem to agree. An amateur yachtsman has assured me, I think mistakenly, that the high tide along the south coast moves from west to east. The Atlantic high tide he tells me swells back around both sides of Ireland and around the north of Scotland, moving up the channel and down the North Sea (would this form a sort of mælstrom where they meet, I wonder?). When I look at tide tables for south coast ports, however, my interpretation is that the tide moves east to west along the Channel coast. I think I prefer to trust the tide tables and to avoid cruising on my friend’s yacht! It seems from the tables that there is a high tide approximately every 12 hours 20 minutes. The double tide effect at Poole Harbour causes a secondary peak that occurs about 4 hours after the main high tide. I don't know why it occurs, perhaps Bean can explain; it is generally lower than the main peak, but there appears to be variation in this, I guess depending on where you are in the spring/neap tide cycle. A similar effect is seen at Southampton due I believe to the Isle of Wight and the two arms of the Solent, but there the two peaks are mostly about the same height with a drop of only a few inches between them, so this has the effect of lengthening the duration of high water – obviously very desirable for a port. Again this effect seems more or less marked depending, I guess, on the spring/neap cycle. Where I have given conclusions rather than facts above they are based on my deductions arrived at from looking at the tide tables so could well be completely erroneous! Two interesting links: http://www.ukho.gov.uk/easytide.htmlhttp://www.alia.ie/sailing/tides.htmldxb
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This has been very interesting indeed! From a glance at the dimensions of Poole Harbour, I would at first guess that the situation is much, much more complicated than first appears. I Googled "double tides" and got this great link for a place in Scotland, which at least states that it's due to the what we call the bottom topography (which is what I suspected all along): http://www.rampantscotland.com/know/blknow31.htmI think to get a good, definitive answer to your question may take some hunting in research papers. Perhaps someone's done a model of the water level and currents in Poole Harbour for a thesis or something. Indeed, from the bit I've read in my book (an introductory oceanography book with merely a single chapter on tides) it would be quite complicated! And from looking at the map, with two sets of narrows and Brownsea island in the middle - I'd say it must be quite complicated - no simple rectangular box for this model! Edit: Oh! Oh! I've found something great, and not technical! Try http://www.weston.org.uk/tides.htm. (I am reading it right now, haven't finished it yet. Just wanted to post in case you were still on Board!)
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OK, dxb, here you go. Online, I found a reference to a book:
Author = Officer, Charles B.
Title = Physical Oceanography of Estuaries (and Associated Coastal Waters)
Publisher = John Wiley & Sons
Year = 1976
Pages = 465
ISBN = 0-471-65278-4
Apparently, it has a chapter which has a section dealing with tides at Solent, etc. So there you go! In a free moment maybe you or I will pick it up from a university library and have a gander at it!
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Hi y'all. I have moved these posts to the Spendrift thread. I'd hate to see such interesting material lost in cyberspace.
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crossthreading.
Bean: tides at Solent.
I think UK usage would be tides in the Solent.
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Bean, thanks for the links and the book ref. In my bookshop browsing I shall keep an eye open for it. Meanwhile there are all the links that have come out of this discussion to explore.
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I had an unpleasant experience with a "sinusoidal" tide. My brother forgot to mention he had used up all the shear pins that protected outboard motor when propeller got tangled in seaweed. My father and I were half a mile down the channel from the mooring place when some weed caused pin to shear, and we found there was no spare pin. I elected to swim back up the channel to the skiff at our mooring place. When I started, the tide was high, but halfway to my goal, it started to turn, and picked up speed quite rapidly, until I was going back down the channel. I had to swim to channel bank, and walk through horrible ooze filled with sharp broken sheel that cut my bare feet. If I had plotted my progress during the swim it would have made a sort of sinusoidal curve, I now recognize.
One of the most spectacular tides in the world is the one in the Bay of Fundy, which in spring can reach forty feet. Alas the few times I was able to visit the Tidal Bore it was comparatively tame. There is a rather long list of terms used to describe tides, too long, and too easy to forget to be worth posting.
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Yes, I know this thread is getting long, but I have one last thing for dxb on this subject. I was in the library today anyway and went to look at that book. It is basically a review of the scientific work in estuaries up to that date (already more than 25 years ago). I read the bit on the Solent, etc., and found it wasn't very helpful. I asked my supervisor what he thought and we looked at a map and worked it out. The Kelvin waves in the NH, as I said, travel with the coast at their right. If the English Channel is about 100 m deep, the the velocity of the Kelvin waves is about 100 km/h. If you look at a map and picture the tide propagating, first along the north coast of France from west to east. Then since the Channel near Dover is so narrow, the Kelvin wave "sees it" as closed altogether, and instead continues along the south coast of England, in an east-west direction. The distance between the closest point near the Isle of Wight and Cherbourg, France, if you measure along the coastline, is such that it takes about three hours for the tide to work its way around there (i. e. ~300 km). So if, say, it is high tide at Poole, the tide is on its way out at Cherbourg, and though they are some distance apart it is not so far that the tide going out at Cherbourg is "unnoticed" by the water at Poole. There are also probably strong topographical effects as well, and what you get is the tide "meeting itself" in the region between the Solent and Poole Harbour. Whew! What an odyssey. If you have any more questions, do PM me (and don't forget to turn your PMs on in that case). (I think others may not be as interested in this discussion as we are!)
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Thanks Bean, I shall sit down quietly with a map and a glass (scotch!) and think on that. As you say, any more by PM.
dxb
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