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A typical desktop globe is designed to be a geometric sphere
and turn smoothly as you rotate it. Our current planet is much less perfect
– both in shape and in rotation.
The Earth is not a perfect sphere. When he turns on himself
axis – an imaginary line that crosses the North and South poles – it
drifts and wobbles. These movements of the axis of rotation are called scientifically
"polar movement." Measures for the 20e show of the century
as the axis of rotation drifts about 4 inches (10 centimeters) a year. Above
Of course for a century, it's more than 10 meters.
Use observational data and model-based data
20 wholee century, NASA scientists have identified for the first time
three categorized processes responsible for this drift – contemporary
loss of mass mainly in Greenland, glacial rebound and mantle convection.
"The traditional explanation is this unique process,
Glacial rebound, is responsible for this movement of the axis of rotation of the Earth. But
recently, many researchers have speculated that other processes might have
potentially significant effects on him too, "said the first author Surendra
Adhikari from NASA's Jet Propulsion Laboratory in Pasadena, California. "We have assembled
models for a suite of processes considered important for driving
the movement of the axis of rotation. We identified not one but three sets of processes
that are crucial – and the melting of the global cryosphere (especially Greenland)
during the 20the century is one. "
In general, the redistribution of mass on and in the Earth
– such as changes in terrain, ice caps, oceans and mantle flows – affect the
the rotation of the planet. As temperatures rose throughout the 20e
century, the ice mass of Greenland decreased. In fact, a total of about 7,500
gigatons – the weight of over 20 million Empire State Buildings – from Greenland
the ice melted in the ocean during this period. That makes Greenland one of the
the main mass contributors being transferred to the oceans, causing sea level
to climb and, therefore, a drift in the axis of rotation of the Earth.
While ice melting occurs in other places (such as
Antarctica), the location of Greenland makes it a larger contributor
movement.
"There is a
geometric effect only if you have a mass that is 45 degrees from the North Pole
– which is Greenland – or
the South Pole (like the Patagonian glaciers), it will have a greater impact on
move the axis of rotation of the Earth rather than a mass that is right next to the pole, "said
co-author Eric Ivins, also from JPL.
Previous studies have identified ice bounce as key
contributing to the long-term polar movement. And what is the glacial rebound? During the
last ice age, heavy glaciers depressed the Earth's surface, much like a mattress
depresses when you sit on it. As the ice melts or is removed, the earth slowly
returns to its original position. In the new study, which relied heavily on
a statistical analysis of this rebound, scientists understood that glacial
the rebound is probably responsible for only a third of the polar drift
in the 20e century.
The authors argue that mantle convection is the final
third. Coat convection is responsible for the movement of tectonic plates on
Earth's surface. It's basically the circulation of material in the coat
caused by the heat of the Earth's core. Ivins describes it as similar to a pot of
soup placed on the stove. Like the pot, or mantle, heats, the pieces of the soup
start to go up and down, basically
forming a pattern of vertical circulation – just like rocks moving across the Earth
coat.
With these three major contributors identified, scientists
can distinguish the mass changes and polar motion caused by the Earth in the long run
processes over which we have little control of those caused by climate change.
They now know that if the loss of ice in Greenland accelerates, it is likely that the polar movement
will be too.
The paper in Earth and Planetary Science Letters is entitled "What drives the polar movement of the 20th century?" In addition to JPL, the German research center for geosciences, Potsdam, is one of its co-establishments; the University of Oslo, Norway; Technical University of Denmark, Kongens Lyngby; the Geological Survey of Denmark and Greenland, Copenhagen, Denmark; and the University of Bremen, Germany.
An interactive simulation of how several processes contribute to Earth's rotational axis oscillations is available at the following address:
https://vesl.jpl.nasa.gov/sea-level/polar-motion/
News Media Contact
Smith's Spirit
Jet Propulsion Laboratory, Pasadena, California.
818.354.4269
[email protected]
2018-219
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