Tracking Earth's Wobbles Down to the Size of a Cell Phone

http://www.agu.org/sci_soc/prrl/prrl0627.html

American Geophysical Union
26 June 2006
AGU Release No. 06-22
AGU Contact: Harvey Leifert
+1 (202) 777-7507


Tracking Earth's Wobbles Down to the Size of a Cell Phone

WASHINGTON - New technologies are enabling scientists to determine
precisely the extent and causes of Earth's short-term wobbling. Like a
spinning top, Earth wobbles as it rotates on its axis. In fact, it
displays many different wobbling motions, ranging in period from a few
minutes to billions of years. Some of these are well studied, like the
Chandler wobble of 433 days and the annual wobble, which together can
tilt Earth's axis up to 10 meters [30 feet] from its nominal center.

Earth's irregular, shorter term wobbles, lasting a week or so, have
been
more difficult to study, partly because these motions are usually
masked
by those of more prominent wobbles. Now, scientists in Belgium and
France have taken advantage of a quirk in the pattern of large-scale
motions and the advent of the Global Positioning System (GPS) to pin
down short-term wobbles that occurred from November 2005 through
February 2006.

During this period, the Chandler wobble and the annual wobble
essentially cancelled each other out, an event that occurs every 6.4
years, allowing the researchers to focus on the short-period wobbles.
Over these three and a half months, the pole position traced small
loops, ranging in size from that of a sheet of A4 [8-1/2x11 inch] paper
down to that of a cell phone, and it remained within a one meter [yard]
square during these four months.

S??bastien Lambert of the Royal Observatory of Belgium and
colleagues
there and at the Paris Observatory took advantage of the opportunity to
track short-term wobbles, using newly available GPS data that establish
the location of the poles precisely. They then sought to determine why
these motions occurred when they did.

In a paper scheduled to be published 1 July in Geophysical Research
Letters, they conclude that weather patterns in the northern hemisphere
played a significant role. Both the location of high- or low-pressure
centers--for example, over Asia or northern Europe--and the
relationship
of these weather systems to each other played a measurable role in
creating, or "exciting," small, short-term wobbles, they report.

The ocean also affects short-term wobbles, according to Lambert and his
colleagues. They were able to correlate oceanic and atmospheric
pressure
variations with the small observed wobbles during the study period.
Although these forces had been credited by previous researchers with
maintaining the large Chandler wobble, this was the first time that
scientists have been able to demonstrate that day-to-day changes in
atmospheric pressure produce a measurable effect on Earth's rotation.

The study was funded by the Belgian Science Policy Office, the Royal
Observatory of Belgium, and the Paris Observatory.

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FIGURE
A figure illustrating polar motion during the study period is available
at http://www.agu.org/sci_soc/prrl/figures/0622fig1.pdf. It is
adapted
from Figure 1 of the Lambert et al. paper, with milliarcseconds (mas)
in
the paper replaced by centimeters (cm). On Earth's surface, one
milliarcsecond equals about three centimeters [1.2 inches]. This figure
can easily be reproduced life-sized, in whole or in part, showing the
actual extent of the observed polar wobble.

******

[Note: Regarding the Chandler wobble, see AGU press release 02-21 of 17
July 2000:
http://www.agu.org/sci_soc/prrl/prrl0021.html]

------------------------------------------------------------------------

Notes for journalists:

Journalists (only) may obtain a pdf copy of this paper upon request to
Jonathan Lifland: . Please
provide your name, name of publication, phone, and email address. The
paper and this press release are not under embargo.

Title:

"Rapid variations in polar motion during the 2005-2006 winter season"

Authors:

S??bastien B. Lambert: Research Assistant, Royal Observatory of
Belgium,
Brussels, Belgium

Christian Bizouard: IERS Earth Orientation Parameter Center, Paris
Observatory, Paris, France

V??ronique M. Dehant: Head of Time, Earth Rotation, and Space
Geodesy
Section, Royal Observatory of Belgium, Brussels, Belgium

Citation:

Lambert, S. B., C. Bizouard, and V. Dehant, Rapid variations in polar
motion during the 2005-2006 winter season, Geophys. Res. Lett., 33,
L13303, doi:10.1029/2006GL026422.

Contact information for author:

S??bastien B. Lambert: +32 2 373 0312 or


[Note: Attending a meeting 27-28 June, may be reachable on mobile
phone:
+33 609 51 13 23]

Christian Bizouard: +33 1 40 51 23 35 or


V??ronique Dehant: +32 2 373 0266 or