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Candy
2004-May-17, 08:38 PM
I just found this on a theory of why the Earth wobbles (http://dailynews.att.net/cgi-bin/news?e=pub&dt=040517&cat=science&st=scienced82kd9g o0&src=ap). "The discovery provides scientists with another means to determine whether Earth is undergoing global warming". Check it out, I never knew GPS was used for tracking the movement of water, either.

swansont
2004-May-17, 10:45 PM
I just found this on a theory of why the Earth wobbles (http://dailynews.att.net/cgi-bin/news?e=pub&dt=040517&cat=science&st=scienced82kd9g o0&src=ap). "The discovery provides scientists with another means to determine whether Earth is undergoing global warming". Check it out, I never knew GPS was used for tracking the movement of water, either.


Well, I did, but then I work literally across the hall from folks who do this sort of stuff. More info here (http://maia.usno.navy.mil/eo/whatiseop.html)

Brady Yoon
2004-May-17, 11:48 PM
I thought it the Earth wobbled because of the gravitational competition between the Sun and the Moon.

Candy
2004-May-18, 12:43 AM
I thought it the Earth wobbled because of the gravitational competition between the Sun and the Moon. I think Swansont was talking about the GPS, but I could be wrong - as usual. :oops: I have googled to find more information from the Geophysical Research Letters, but I can't find anything. This is interesting, though! Water shifting making the Earth wooble. :-k

GarethB
2004-May-18, 02:51 AM
And now for the obvious question. If it's caused by water movement, does it wobble in a clockwise or anticlockwise direction? :D

Jpax2003
2004-May-18, 05:42 AM
I thought the earth wobbled because of precession, I must have been thinking of something else. How does GPS gather information about the ocean height? Does someone/something need to on the ocean surface to detect variances in the signal? I didn't think GPS sats scanned the earth like radar mapping. Or is it just derived from calculating orbital eccentricities cause by gravitational deviations on the earth by low flying sats?

BTW the opposite of clockwise is counter-clockwise, not anticlockwise.

Musashi
2004-May-18, 06:01 AM
I believe anticlockwise is valid as well.

Candy
2004-May-18, 06:05 AM
BTW the opposite of clockwise is counter-clockwise, not anticlockwise. That is what I thought to, until I googled it. Counterclockwise is Anticlockwise (http://thesaurus.maths.org/mmkb/entry.html?action=entryByConcept&id=398) at definition level 2 (sounds secretive): The opposite of clockwise; the way the Earth would be turning if you could look at it from above the North Pole.

tusenfem
2004-May-18, 07:45 AM
Hey Candy,
I think googling will not work, as you have to subscribe to GRL (which I have because of my profession).



I thought it the Earth wobbled because of the gravitational competition between the Sun and the Moon. I think Swansont was talking about the GPS, but I could be wrong - as usual. :oops: I have googled to find more information from the Geophysical Research Letters, but I can't find anything. This is interesting, though! Water shifting making the Earth wooble. :-k

As the abstracts are public domain, I think I can copy that here:



A fluid, mobile atmosphere and oceans surrounds the solid Earth and upon its land surface lays a continually changing distribution of ice, snow, and ground water. The changing distribution of mass associated with the motion of these surficial fluids changes the Earth's rotation by changing its inertia tensor and changes the Earth's shape by changing the load on the solid Earth. It has recently been demonstrated that large-scale changes of the Earth's shape, and hence of the mass load causing the Earth's shape to change, can be measured using the global network of GPS receivers. Here, the degree-2 mass load coefficients determined from GPS data are compared with those obtained from Earth orientation observations from which the effects of tides, winds, and currents have been removed. Good agreement is found between these two estimates of the degree-2 mass load, particularly at seasonal frequencies.

Well tht gives you some idea what they have done. To get the whole paper, go to the Geophysiscs library (or contact me).

Kaptain K
2004-May-18, 10:54 AM
The opposite of clockwise is withershins! 8)

Candy
2004-May-18, 02:04 PM
Well that gives you some idea what they have done. To get the whole paper, go to the Geophysiscs library (or contact me). Wow, your portion of the paper was grand. So what exactly does the paper mean? Does the Earth wobble because of water shifting? Fascinating. Will or when will this be set in stone? Or is it just a theory?

swansont
2004-May-18, 05:29 PM
Does the Earth wobble because of water shifting? Fascinating. Will or when will this be set in stone? Or is it just a theory?

There are lots of small effects that can't be predicted, since some of them depend on the weather. And who can predict the weather? :)

Jpax2003
2004-May-18, 07:02 PM
BTW the opposite of clockwise is counter-clockwise, not anticlockwise. That is what I thought to, until I googled it. Counterclockwise is Anticlockwise (http://thesaurus.maths.org/mmkb/entry.html?action=entryByConcept&id=398) at definition level 2 (sounds secretive): The opposite of clockwise; the way the Earth would be turning if you could look at it from above the North Pole. OK, I may have been wrong. But now I think the opposite of Clockwise is Digital. Or is the opposite of clockwise Lefty-loosey?

skrap1r0n
2004-May-18, 07:24 PM
And now for the obvious question. If it's caused by water movement, does it wobble in a clockwise or anticlockwise direction? :D

That would all depend on whether or not your in the northern or southern semisphere :lol:

(if he can say anticlockwise I can say semisphere :P )

tusenfem
2004-May-19, 08:41 AM
Well that gives you some idea what they have done. To get the whole paper, go to the Geophysiscs library (or contact me). Wow, your portion of the paper was grand. So what exactly does the paper mean? Does the Earth wobble because of water shifting? Fascinating. Will or when will this be set in stone? Or is it just a theory?

Glad you liked my addition to this thread.
I have not really read the paper (downloaded and read the abtract), but I can imagine that the presence of the non-uniform distribution of land and water do give rise to a torque on the earth's rotation. This will make it wobble, mmm, now I start to sound like good-ole Nancy :lol:
I don't have time right now to read it, as I am preparing for a trip, and have to finish my presentation and some work :cry:

Eroica
2004-May-19, 11:10 AM
The opposite of clockwise is withershins! 8)
And the opposite of withershins is deasil (deshil, deiseal etc) 8)

Jpax2003
2004-May-20, 05:17 AM
Well that gives you some idea what they have done. To get the whole paper, go to the Geophysiscs library (or contact me). Wow, your portion of the paper was grand. So what exactly does the paper mean? Does the Earth wobble because of water shifting? Fascinating. Will or when will this be set in stone? Or is it just a theory?

Glad you liked my addition to this thread.
I have not really read the paper (downloaded and read the abtract), but I can imagine that the presence of the non-uniform distribution of land and water do give rise to a torque on the earth's rotation. This will make it wobble, mmm, now I start to sound like good-ole Nancy :lol:
I don't have time right now to read it, as I am preparing for a trip, and have to finish my presentation and some work :cry:So the gravitic variations caused by the uneven distribution of mass near the earth's surface causes sweeping arms of the earth?

milli360
2004-May-20, 11:45 AM
The opposite of clockwise is withershins! 8)
Or, better, widdershins (http://www.bartleby.com/61/76/W0147600.html). :)

I thought the earth wobbled because of precession, I must have been thinking of something else.
Yes, there is more than one "wobble".

This wobble is the Eulerian free wobble. If you were to crang the Earth, it would ring like a bell. The vibration that would result is the free wobble, known as the Chandler Wobble after the guy who first detected it. It has a period of about 14 months.

The seasonal wobble, which these guys seem to have focussed on, is related but it is driven by the seasonal changes, and has a period of 12 months. The actual wobble is a beat of the two.

One of the big mysteries of geophysics is how the Chandler Wobble is maintained--its frequency signature suggests that it would have a halflife of about 50 or 60 years, but it has been going strong for over a hundred years. One of the co-authors of that paper, Richard Gross, announced four years ago that he had discovered the solution, in the meteorological effects.

The seasonal forcing has a narrow influcence and doesn't "leak" over into the Chandler frequency.

genebujold
2004-May-20, 01:19 PM
I just found this on a theory of why the Earth wobbles (http://dailynews.att.net/cgi-bin/news?e=pub&dt=040517&cat=science&st=scienced82kd9g o0&src=ap). "The discovery provides scientists with another means to determine whether Earth is undergoing global warming". Check it out, I never knew GPS was used for tracking the movement of water, either.

Good one! Yeah, it's the GPS water-tracking mod they put into orbit last year...

Isn't Reno where old retarded gamblers go to die (or spend their last paycheck, whichever comes first)?

I'm kidding folks... And I do know a thing or two about GPS.

The military uses a PLGR (Programmable Lightweight GPS Receiver). One of its modes is "survey," which requires the user to stand still for a couple of minutes while it averages the readings over time.

It's very accurate - but not to within 3/20 of an inch.

Nevertheless, the time cycle is fairly short (minute or two). If you were to drop a radiosonde into the ocean from a P3 Orien, and that radiosonde were equipped with a GPS that similarly averages signals, but over a much longer time span, say an hour or so, and reported that back to the plane (P3), then conceivably, yes - this accuracy might be possible.

However, local variations in tides (even the middle of the ocean has tides), the effect of underwater structures like seamounts and ridges in the ocean's currents, I would think would effect the average surface height by more than 3/20th of a inch.

And I'm quite sure local pressure variants effect it as well - the difference between standard atmospheric conditions (32.2 inches of mercury) and a tropical storm (28 inches of mercury) is enough pressure to cause water to rise/fall by .21304 inches - that's 2/10ths of an inch, or 4/20ths, which is an error larger than their accuracy of 3/20th of an inch.

In cities and towns they use one of two methods for surveying. One is differential GPS, but that's not adequate enough for the final measure. The name of the second one escapes me, but a friend of mine who used to do surveys says it givens them an accuracy of about the size of a silver dollar, and that's using equipment that's not being tossed up and down on the waves.

As a result, I'm leary of his claims of accuracy with respect to the measurements - there are so many factors that can throw it off, and in the absolute best of conditions, current GPS technology on the satellites themselves just isn't that precise, and amplifying technology located here on the ground isn't that precise, either.

About the only thing I can think of is that they might have anchored a floating GPS buoy in a harbor and used GPS equipment to compare the signal between it and a nearby land-mounted GPS receiver.

But I still question the accuracy of 3/20th of an inch!

genebujold
2004-May-20, 01:26 PM
The seasonal forcing has a narrow influcence and doesn't "leak" over into the Chandler frequency.

Sort of like shouting in an empty house maintains the sound energy level because the walls reflect the energy back while there's little in the room to dampen it?

milli360
2004-May-20, 01:57 PM
The seasonal forcing has a narrow influcence and doesn't "leak" over into the Chandler frequency.

Sort of like shouting in an empty house maintains the sound energy level because the walls reflect the energy back while there's little in the room to dampen it?
No, it's just that there is no slop-over. The 12-month signal is wider than the 14-month, but its not wide enough to excite the 14-month significantly. So, the 12-month signal is forced (by the "shouting") but it doesn't cause enough of the 14-month wobble to make a difference. The damping of the 14-month signal appears to have been strong enough to have caused it to die out, but it hasn't.

genebujold
2004-May-20, 03:06 PM
The seasonal forcing has a narrow influcence and doesn't "leak" over into the Chandler frequency.

Sort of like shouting in an empty house maintains the sound energy level because the walls reflect the energy back while there's little in the room to dampen it?
No, it's just that there is no slop-over. The 12-month signal is wider than the 14-month, but its not wide enough to excite the 14-month significantly. So, the 12-month signal is forced (by the "shouting") but it doesn't cause enough of the 14-month wobble to make a difference. The damping of the 14-month signal appears to have been strong enough to have caused it to die out, but it hasn't.

Resonance can be strengthened by off-frequency externals, provided their close enough to the original (or a multiple). Generally speaking, 20% is the limit, and your 14-month vs 12-month difference falls within the 20% rule.

milli360
2004-May-20, 03:41 PM
Resonance can be strengthened by off-frequency externals, provided their close enough to the original (or a multiple). Generally speaking, 20% is the limit, and your 14-month vs 12-month difference falls within the 20% rule.
20% of what? Harmonics can be excited, and they are 100% off. :)

In this case, the power spectrum shows too sharp of peaks at 12m and 14m for them to cross over. They don't overlap at all.

swansont
2004-May-21, 12:57 PM
The military uses a PLGR (Programmable Lightweight GPS Receiver). One of its modes is "survey," which requires the user to stand still for a couple of minutes while it averages the readings over time.

It's very accurate - but not to within 3/20 of an inch.

Nevertheless, the time cycle is fairly short (minute or two). If you were to drop a radiosonde into the ocean from a P3 Orien, and that radiosonde were equipped with a GPS that similarly averages signals, but over a much longer time span, say an hour or so, and reported that back to the plane (P3), then conceivably, yes - this accuracy might be possible.

However, local variations in tides (even the middle of the ocean has tides), the effect of underwater structures like seamounts and ridges in the ocean's currents, I would think would effect the average surface height by more than 3/20th of a inch.

And I'm quite sure local pressure variants effect it as well - the difference between standard atmospheric conditions (32.2 inches of mercury) and a tropical storm (28 inches of mercury) is enough pressure to cause water to rise/fall by .21304 inches - that's 2/10ths of an inch, or 4/20ths, which is an error larger than their accuracy of 3/20th of an inch.

In cities and towns they use one of two methods for surveying. One is differential GPS, but that's not adequate enough for the final measure. The name of the second one escapes me, but a friend of mine who used to do surveys says it givens them an accuracy of about the size of a silver dollar, and that's using equipment that's not being tossed up and down on the waves.

As a result, I'm leary of his claims of accuracy with respect to the measurements - there are so many factors that can throw it off, and in the absolute best of conditions, current GPS technology on the satellites themselves just isn't that precise, and amplifying technology located here on the ground isn't that precise, either.

About the only thing I can think of is that they might have anchored a floating GPS buoy in a harbor and used GPS equipment to compare the signal between it and a nearby land-mounted GPS receiver.

But I still question the accuracy of 3/20th of an inch!

(tried this once and it didn't "take." hmmm)

The other mode does carrier-wave measurements, and can be precise to less than a cm.

I haven't read the paper, but I'm pretty sure they are doing land-based measurements with calibrated receivers, not water-borne measurements on buoys. Measure the change in the oblateness of the earth (the J2 term) and from that deduce water movements.

Jpax2003
2004-May-23, 06:30 AM
Yes, there is more than one "wobble".

This wobble is the Eulerian free wobble. If you were to crang the Earth, it would ring like a bell. The vibration that would result is the free wobble, known as the Chandler Wobble after the guy who first detected it. It has a period of about 14 months.

The seasonal wobble, which these guys seem to have focussed on, is related but it is driven by the seasonal changes, and has a period of 12 months. The actual wobble is a beat of the two.

One of the big mysteries of geophysics is how the Chandler Wobble is maintained--its frequency signature suggests that it would have a halflife of about 50 or 60 years, but it has been going strong for over a hundred years. One of the co-authors of that paper, Richard Gross, announced four years ago that he had discovered the solution, in the meteorological effects.

The seasonal forcing has a narrow influcence and doesn't "leak" over into the Chandler frequency.Is this related in anyway to the work being done at www.elfrad.com ?

milli360
2004-May-23, 12:12 PM
This wobble is the Eulerian free wobble.Is this related in anyway to the work being done at www.elfrad.com ?
As near as I can tell, it has nothing to do with it. But I didn't click on the Indian Spring Herbs or Wild Foods For Survival links. :)

Candy
2004-May-24, 11:27 PM
Well that gives you some idea what they have done. To get the whole paper, go to the Geophysiscs library (or contact me). Wow, your portion of the paper was grand. So what exactly does the paper mean? Does the Earth wobble because of water shifting? Fascinating. Will or when will this be set in stone? Or is it just a theory?

Glad you liked my addition to this thread.
I have not really read the paper (downloaded and read the abtract), but I can imagine that the presence of the non-uniform distribution of land and water do give rise to a torque on the earth's rotation. This will make it wobble, mmm, now I start to sound like good-ole Nancy :lol:
I don't have time right now to read it, as I am preparing for a trip, and have to finish my presentation and some work :cry:

At you leisure, I would like a copy of the paper. Thank you. My email is candy.stair@att.net I really enjoy reading about this subject.

milli360
2004-May-25, 10:08 AM
I can imagine that the presence of the non-uniform distribution of land and water do give rise to a torque on the earth's rotation. This will make it wobble
Not necessarily. Isostasy basically balances things out, so that doesn't really have anything to do with it.