How come the Chandler wobble hasn’t dampened out?
03-Dec-1999
Cecil mentions that there are two leading theories as to why this occurs, one is seasonal variations and the other is planetary disturbances, such as earthquakes and the like.
My question is, does the Chandler effect (or something similar to it) occur in any of other planets? Are we able to notice such a thing if it does, or do our instruments not have enough accuracy to measure such a thing.
If it does occur in any, are we stuck with the same theories still (such as seasonal change)?
I ask because if a planet had it, such as mars which has no such seasonal variation (to my knowledge…which I admit is limited on this subject), would not one be able to gauge these two theories better?
… oh well… this is the easy way, I guess I’ll go try looking it up myself as well.
Oddly enough, Ted, this thread, started by yours truly, dropped off the bottom of the board just before you posted. Although the links and discussion contained therein don’t directly answer your question, the recently published hypothesis discussed (hypothesis = Chandler wobble is caused by ocean pressure fluctuations) suggests that the Chandler wobble might not occur on other planets. Although, perhaps, a heavy planet like Jupiter might have a dense enough atmosphere to cause pressure fluctuations of enough significance to make the planet wobble.
Oh, and let me do my best (if sadly lacking) Arnold Winkelried imitiation by 1) being the first one to welcome you to the Straight Dope, and 2) pointing out that the column you are referring to can be found on-line here.
I read the article but one thing does puzzle me about it:
I did not have an opportunity to read Gross’s actual paper and this excerpt for some reason seems to shed a bit of doubt in my mind.
For some reason it reads like Gross’s method is lacking. It reads to me as if he was able to account for only 2/3rd’s of the Chandler wobble and just pulled out one of the other hypotheses to account for the rest of it. I’m not saying he is wrong (I am certain he and others have a much greater knowledge of this than myself) but his answer seems to be incomplete by a 1/3rd.
Also, to create the regularity of the Chandler wobble, would the fluctuations in the atmospheric pressure need to be in a pattern that coincides with that of the ocean bottom pressure? If they are not wouldn’t there be less of an effect on the Chandler wobble?
Welcome to the SDMB, and thank you for posting your comment.
Please include a link to Cecil’s column if it’s on the straight dope web site.
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Cecil’s column can be found on-line at the link provided by zut.
The patterns wouldn’t have to coincide, but if they weren’t, there might be less of an effect. Dr. Gross has studied the wobble for twenty years, and is apparently dedicated to it. I haven’t seen his paper, but I’m pretty certain he would have accounted for all such effects.
There are two wobbles, one at 12 months, and one at 14 months. The 12 month wobble is forced by the seasonal variations, but the 14 month wobble is the Chandler wobble (see Cecil’s column), and it is the natural frequency of the earth. It’s as if the earth is a big tuning fork–if you hit it, it’ll ring at the Chandler wobble frequency, no matter how you hit it. However,after it has started ringing, if you hit it just right, you could stop it from ringing. Calculating the right relationship between the ocean-bottom pressure changes and the wobble was probably the hard part.
I’ve been reading a short summary of Gross’ discovery in Science magazine.
As they explain it, Gross has found an explanation for close to all the wobble.
They have a cute diagram which covers all the causes.
Melting of ice
Atmospheric loading
Groundwater
Winds
Sea level loading
Gravitational pull of sun and moon
Earthquakes
Continental drift
Ocean currents
Some of these seem more powerful then others, but it sort of makes sense that the slow, persistent work of the winds would keep that tuning fork humming.
As for the 1/3, 2/3 thing, as one geophysicst points out, “The oceans are mainly wind-driven, so you have the atmosphere driving the whole thing”
The article claims that being able to predict the wobble by measuring those forces that are its source will help in guidance of spacecraft. I had no idea the wobble was significant enough to cause any problems with tracking spacecraft!
More than a century after its discovery, a scientist has at last solved the puzzle of the “Chandler wobble.” In 1891 Seth Carlo Chandler determined that Earth’s poles move 6 meters (20 feet) during a 1.2-year cycle. Previous calculations have proven that, without an external force acting, the wobble would dampen after 68 years, yet movement continues. A wide variety of causes have been suggested, but none quite fit the data.
Now Richard S. Gross (Jet Propulsion Laboratory) attributes the 433–day polar deviation primarily to pressure fluctuations at the bottom of the ocean, closing the book on this mystery. His paper, to be published in the August 1st Geophysical Research Letters, concludes that variations in atmospheric pressure account for approximately one third of the source of the wobble, while ocean–bottom pressure fluctuations dominate. The mass of the oceans shift in response to changes in temperature, salinity, and atmospheric winds. This movement changes the pressure exerted on the Earth’s crust, causing a wobble. Gross applied numerical models of the ocean to data on the polar motion taken throughout a 10–year period to achieve his results.