|
|
Joined: Jan 2001
Posts: 1,156
old hand
|
old hand
Joined: Jan 2001
Posts: 1,156 |
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.
|
|
|
|
|
Joined: Nov 2000
Posts: 866
old hand
|
|
old hand
Joined: Nov 2000
Posts: 866 |
> 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
|
|
|
|
|
Joined: Apr 2000
Posts: 3,065
Carpal Tunnel
|
|
Carpal Tunnel
Joined: Apr 2000
Posts: 3,065 |
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
Bingley
|
|
|
|
|
Joined: Jan 2001
Posts: 1,156
old hand
|
|
old hand
Joined: Jan 2001
Posts: 1,156 |
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.
|
|
|
|
|
Joined: Apr 2000
Posts: 3,065
Carpal Tunnel
|
|
Carpal Tunnel
Joined: Apr 2000
Posts: 3,065 |
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
Bingley
|
|
|
|
|
Joined: Aug 2001
Posts: 2,605
Carpal Tunnel
|
|
Carpal Tunnel
Joined: Aug 2001
Posts: 2,605 |
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.
|
|
|
|
|
Joined: Nov 2000
Posts: 3,439
Carpal Tunnel
|
|
Carpal Tunnel
Joined: Nov 2000
Posts: 3,439 |
"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!
|
|
|
|
|
Joined: Mar 2000
Posts: 6,511
Carpal Tunnel
|
|
Carpal Tunnel
Joined: Mar 2000
Posts: 6,511 |
... are what I get during allergy season.
|
|
|
|
|
Joined: Dec 2000
Posts: 144
member
|
|
member
Joined: Dec 2000
Posts: 144 |
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!
|
|
|
|
|
Joined: Dec 2000
Posts: 13,803
Carpal Tunnel
|
|
Carpal Tunnel
Joined: Dec 2000
Posts: 13,803 |
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?
|
|
|
|
Forums16
Topics13,913
Posts229,687
Members9,187
| |
Most Online3,341
Dec 9th, 2011
|
|
|
0 members (),
217
guests, and
3
robots. |
|
Key:
Admin,
Global Mod,
Mod
|
|
|
|
