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.html
http://oceanworld.tamu.edu/text/students/waves/waves1.htm, and continue to successive pages.
http://www.weathernotebook.org/transcripts/2001/04/18.html

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.

An on-the-spot news account of this Chicago seiche: http://www.kacm.com/Tidalwave.htm

Information 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."

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.

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

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.

stales

Thank you, milum. Fascinating! I now know what I'm going to be doing all this afternoon.
[rushing off to find that book -e]

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.

stales

(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)

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!

DOWN UNDER: SOLVED

It'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."

Ha ha ha. Boil me in Kangaroo oil, We live in a land down under after all."

Is the operative word here "live"?

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!

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.

...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?

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

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..

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.

tides

What 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.html


The Only WO'N!

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!!!

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.

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.

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.

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.

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

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.

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.

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?

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

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?)

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!

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!

>>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!)

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.

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.

> 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

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?

Bingley

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.

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.

Bingley

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.