NASA Study Solves Two Mysteries About Wobbling Earth

Posted: April 9, 2016 by tallbloke in Astrophysics, Clouds, solar system dynamics, weather

sun-earth-moon

Using satellite data on how water moves around Earth, NASA scientists have solved two mysteries about wobbles in the planet’s rotation — one new and one more than a century old. The research may help improve our knowledge of past and future climate.

Although a desktop globe always spins smoothly around the axis running through its north and south poles, a real planet wobbles. Earth’s spin axis drifts slowly around the poles; the farthest away it has wobbled since observations began is 37 feet (12 meters). These wobbles don’t affect our daily life, but they must be taken into account to get accurate results from GPS, Earth-observing satellites and observatories on the ground.

In a paper published today in Science Advances, Surendra Adhikari and Erik Ivins of NASA’s Jet Propulsion Laboratory, Pasadena, California, researched how the movement of water around the world contributes to Earth’s rotational wobbles. Earlier studies have pinpointed many connections between processes on Earth’s surface or interior and our planet’s wandering ways. For example, Earth’s mantle is still readjusting to the loss of ice on North America after the last ice age, and the reduced mass beneath that continent pulls the spin axis toward Canada at the rate of a few inches each year. But some motions are still puzzling.

A Sharp Turn to the East

Around the year 2000, Earth’s spin axis took an abrupt turn toward the east and is now drifting almost twice as fast as before, at a rate of almost 7 inches (17 centimeters) a year. “It’s no longer moving toward Hudson Bay, but instead toward the British Isles,” said Adhikari. “That’s a massive swing.” Adhikari and Ivins set out to explain this unexpected change.

Scientists have suggested that the loss of mass from Greenland and Antarctica’s rapidly melting ice sheet could be causing the eastward shift of the spin axis. The JPL scientists assessed this idea using observations from the NASA/German Aerospace Center Gravity Recovery and Climate Experiment (GRACE) satellites, which provide a monthly record of changes in mass around Earth. Those changes are largely caused by movements of water through everyday processes such as accumulating snowpack and groundwater depletion. They calculated how much mass was involved in water cycling between Earth’s land areas and its oceans from 2003 to 2015, and the extent to which the mass losses and gains pulled and pushed on the spin axis.

Adhikari and Ivins’ calculations showed that the changes in Greenland alone do not generate the gigantic amount of energy needed to pull the spin axis as far as it has shifted. In the Southern Hemisphere, ice mass loss from West Antarctica is pulling, and ice mass gain in East Antarctica is pushing, Earth’s spin axis in the same direction that Greenland is pulling it from the north, but the combined effect is still not enough to explain the speedup and new direction. Something east of Greenland has to be exerting an additional pull.

The researchers found the answer in Eurasia. “The bulk of the answer is a deficit of water in Eurasia: the Indian subcontinent and the Caspian Sea area,” Adhikari said.

The finding was a surprise. This region has lost water mass due to depletion of aquifers and drought, but the loss is nowhere near as great as the change in the ice sheets.

So why did the smaller loss have such a strong effect? The researchers say it’s because the spin axis is very sensitive to changes occurring around 45 degrees latitude, both north and south. “This is well explained in the theory of rotating objects,” Adhikari explained. “That’s why changes in the Indian subcontinent, for example, are so important.”

New Insight on an Old Wobble

In the process of solving this recent mystery, the researchers unexpectedly came up with a promising new solution to a very old problem, as well. One particular wobble in Earth’s rotation has perplexed scientists since observations began in 1899. Every six to 14 years, the spin axis wobbles about 20 to 60 inches (0.5 to 1.5 meters) either east or west of its general direction of drift. “Despite tremendous theoretical and modeling efforts, no plausible mechanism has been put forward that could explain this enigmatic oscillation,” Adhikari said.

Lining up a graph of the east-west wobble during the period when GRACE data were available against a graph of changes in continental water storage for the same period, the JPL scientists spotted a startling similarity between the two. Changes in polar ice appeared to have no relationship to the wobble — only changes in water on land. Dry years in Eurasia, for example, corresponded to eastward swings, while wet years corresponded to westward swings.

When the researchers input the GRACE observations on changes in land water mass from April 2002 to March 2015 into classic physics equations that predict pole positions, they found that the results matched the observed east-west wobble very closely. “This is much more than a simple correlation,” coauthor Ivins said. “We have isolated the cause.”

The discovery raises the possibility that the 115-year record of east-west wobbles in Earth’s spin axis may, in fact, be a remarkably good record of changes in land water storage. “That could tell us something about past climate — whether the intensity of drought or wetness has amplified over time, and in which locations,” said Adhikari.

“Historical records of polar motion are both globally comprehensive in their sensitivity and extraordinarily accurate,” said Ivins. “Our study shows that this legacy data set can be used to leverage vital information about changes in continental water storage and ice sheets over time.”

GRACE is a joint NASA mission with the German Aerospace Center (DLR) and the German Research Center for Geosciences (GFZ), in partnership with the University of Texas at Austin. For more information on the mission, visit:

http://grace.jpl.nasa.gov

http://www.csr.utexas.edu/grace

Comments
  1. oldbrew says:

    No surprise that this story has been hi-jacked by warmists…

    ‘Global warming is making the Earth tilt on its axis – and shrinking India is pushing the North Pole towards London’
    http://www.independent.co.uk/environment/climate-change/global-warming-is-making-the-earth-tilt-on-its-axis-and-shrinking-india-is-pushing-the-north-pole-a6975611.html

    Didn’t the Independent once market itself as a serious news outlet?

  2. Oldmank says:

    From oldbrew’s link: “Since observations began, the North Pole has been drifting southwards towards Hudson Bay, Canada, at a rate of 10 centimetres a year. This is thought to stem from the collapse of the giant Laurentide Ice Sheet in North America thousands of years ago.

    But since the early part of this century the direction of the axis’ has shifted in a different direction and is now moving about 17 centrimetres east a year.”

    All this shifting; maybe that’s why polar bears go about on all-fours.

    Seriously, so then what they have been thinking all along for so long is manifestly wrong. The earth can re-adjust its axial orientation at short notice.

  3. p.g.sharrow says:

    I see FACTS, that the position of the center of rotation is moving. And FICTION,Theory, that the movement of water is the cause, maybe, couldbe, mightbe, etc. The only cause that is not pointed to is Continental Drift, The one thing that contains enough mass to effect the kind changes seen. The mass of the Hydrosphere is a VERY thin veneer on this huge, semi molten, Iron ball that is covered with a slag crust of Oxides..pg

  4. ivan says:

    P.G. They can’t get global warming in if they consider anything like Continental Drift and if there is nothing about global warming then the research funds dry up.

  5. Oldmank says:

    There are other issues that don’t figure in the last couple of k yrs but that figure prominently since the last ice age. Like submergence.

    https://www.thevintagenews.com/2016/03/19/sonar-equipment-used-map-2012-olympic-water-areas-finds-something-extraordinary/?src=fba&type=wca&page=tvn

    The Med is a prime area for that.

  6. p.g.sharrow says:

    @Ivan, you noticed that funding gimmy too. Lol…;-) pg

  7. husq says:

    The Papyrus Harris speaks of a colossal catastrophe of fire and water when “the North becomes the South. The Earth turned round on itself”
    The priets of Luxor “Twice in past ages the Sun used to rise in a different quarter from where it rises now and twice it was wont to set in the
    east instead of the west”

    Plato wrote about this in Politicus: “In certain periods, the universe has its present rotating movement and in other periods it turns in the opposite direction… Of all the changes that take place in the sky, this reversal is the biggest and the most complete.”

    Astonishingly what the elders are saying is global warming is not the whole story…

    http://www.thebigwobble.org/2014/12/their-sky-has-changed-inuit-elders.html

  8. Oldmank says:

    @ husq: Plato was more clear about earth axial shifting ” Plato: “now this has the form of a myth but really signifies a declination of the bodies of the heavens—”. For an observer on earth that is what one sees.

    Husq says “Astonishingly what the elders are saying is global warming is not the whole story…”. Lonnie Thompson noted increased rate of melting of the Quelccaya ice cap now nearly seventy years ago. That is an equatorial region, not polar.

    https://tallbloke.wordpress.com/2014/12/24/dodwells-surprising-study-of-the-obliquity-of-the-ecliptic/

  9. Russ Wood says:

    In the 70’s, Alan Eckert wrote a disaster novel “The HAB Theory”, using some current science to extrapolate an ‘overturn’ of the Earth’s axes. ( https://en.wikipedia.org/wiki/The_HAB_Theory )
    I wonder just what IS happening? Fact or fiction?

  10. jdmcl says:

    I wonder why NASA ignored the elephant that is the ENSO. It supposedly sloshes huge amounts of water around the Pacific, piling it up near south east Asia during La Nina events but flattening out the ocean during El Nino. It’s also the determinant of rainfall for much of the world.
    The report on the NASA webpage uses time periods that are far too coarse and says nothing about the wobble prior to year 2000, which means that it’s not helpful for testing any hypothesis.

  11. dscott says:

    I doubt the answer to their mystery is the location of water mass on earth, the change in water mass specific to a location is a result not a cause of earth’s wobble. It is well known that the distribution of water and land mass (bulge) at the equator is determined by the Earth’s rotation, not the other way around. They have it bass ackwards.

    The fact is the obliquity of Earth is declining so it’s not a mystery that the change in obliquity affects the spin and the wobble itself. Earth’s rotation rate measured in L.O.D. changes which in turn changes the axis point of the rotation. For an exaggerated example spin a top or gyroscope and observe the wobble as the rpm slows or if you forcibly change the tilt. Remember that the gyroscopic effect of a spinning object is to “resist” any change in orientation of the object in space and that resistance is going to manifest itself in wobble, orientation, and rotational spin rates as those forces find a new balance point. The Earth’s obliquity is a major source of influence because it is being affected by outside objects such as the Moon, the Sun and other planets and maybe even the galactic plane itself.

  12. Paul Vaughan says:

    Some links so we can look back on this in the future — at least they’re maybe helping clue climate scientists in to the necessity for climate change narratives to be consistent with the EOP (earth orientation parameter) record:

    http://www.scientificamerican.com/article/earth-is-tipping-because-of-climate-change1/

    http://www.nasa.gov/feature/nasa-study-solves-two-mysteries-about-wobbling-earth

    The actual paper — it’s actually not paywalled:

    Adhikari & Ivins (2016). Climate-driven polar motion: 2003-2015.
    http://advances.sciencemag.org/content/advances/2/4/e1501693.full.pdf

    I’ll have to look into this more carefully (no time for it today) after noticing what they’re doing in figure 1 (ASSUMPTION OF LINEARITY like wtf???):

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