Космологија

Plate tectonics may control reversals in the Earth's magnetic field

The Earth's magnetic field has reversed many times at an irregular rate throughout its history. Long periods without reversal have been interspersed with eras of frequent reversals. What is the reason for these reversals and their irregularity? Researchers from CNRS and the Institut de Physique du Globe(1) have shed new light on the issue by demonstrating that, over the last 300 million years, reversal frequency has depended on the distribution of tectonic plates on the surface of the globe. This result does not imply that terrestrial plates themselves trigger the switch over of the magnetic field. Instead, it establishes that although the reversal phenomenon takes place, in fine, within the Earth's liquid core, it is nevertheless sensitive to what happens outside the core and more specifically in the Earth's mantle. This work is published on 16 October 2011 in Geophysical Research Letters.

The Earth's magnetic field is produced by the flow of liquid iron within its core, three thousand kilometers below our feet. What made researchers think of a link between plate tectonics and the magnetic field? The discovery that convective liquid iron flows play a role in magnetic reversals: experiments and modeling work carried out over the last five years have in fact shown that a reversal occurs when the movements of molten metal are no longer symmetric with respect to the equatorial plane. This “symmetry breaking” could take place progressively, starting in an area located at the core-mantle boundary (the mantle separates the Earth's liquid core from its crust), before spreading to the whole core (made of molten iron).

Extending this research, the authors of the article asked themselves whether some trace of initial symmetry breakings behind the geomagnetic reversals that have marked the Earth's history, could be found in the only records of large-scale geological shifts in our possession, in other words the movements of continents (or plate tectonics). Some 200 million years ago, Pangaea, the name given to the supercontinent that encompassed almost all of the Earth's land masses, began to break up into a multitude of smaller pieces that have shaped the Earth as we know it today. By assessing the surface area of continents situated in the Northern hemisphere and those in the Southern hemisphere, the researchers were able to calculate a degree of asymmetry (with respect to the equator) in the distribution of the continents during that period.

In conclusion, the degree of asymmetry has varied at the same rhythm as the magnetic reversal rate (number of reversals per million years). The two curves have evolved in parallel to such an extent that they can almost be superimposed. In other words, the further the centre of gravity of the continents moved away from the equator, the faster the rate of reversals (up to eight per million years for a maximum degree of asymmetry).

What does this suggest about the mechanism behind geomagnetic reversals? The scientists envisage two scenarios. In the first, terrestrial plates could be directly responsible for variations in the frequency of reversals: after plunging into the Earth's crust at subduction zones, the plates could descend until they reach the core, where they could modify the flow of iron. In the second, the movements of the plates may only reflect the mixing of the material taking place in the mantle and particularly at its base. In both cases, the movements of rocks outside the core would cause flow asymmetry in the liquid core and determine reversal frequency.
Notes:

1 - Laboratoire de Physique Statistique of ENS (Ecole Normale Supérieure/CNRS/UPMC/Université Paris Diderot) and the Institut de Physique du Globe de Paris (CNRS/IPGP/Université Paris Diderot)
References:

Plate Tectonics May Control Geomagnetic Reversal Frequency. F. Pétrélis, J. Besse, J.-P. Valet. Geophysical Research Letters, 16 October 2011.

http://www2.cnrs.fr/en/1923.htm

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There are many unanswered questions: Why do the portals form every 8 minutes? How do magnetic fields inside the cylinder twist and coil? "We're doing some heavy thinking about this at the Workshop," says Sibeck. 

Meanwhile, high above your head, a new portal is opening, connecting your planet to the sun.

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http://science1.nasa.gov/science-news/science-at-nasa/2008/30oct_ftes/

Соларниот сателит на НАСА, снимил голема експлозија на Сонцето која се случила во огромната група пеги означени како АР 1944

Во прашање е најголемата група сончеви пеги која ја прикажува оваа огромна соларна експлозија.

Оваа група пеги која моментално се наоѓаат на средината на Сонцето кога тоа се набљудува од Земјата, е една од најголемите кои се забележани во последните десет години.

Експертите предвидуваат дека оваа соларна експлозија ќе започна геомагнетна бура во магнетното поле на Земјата кога бранот соларна плазма ќе дојде до земјата во наредните неколку денови. [1]

Sun Unleashes 1st Major Solar Flare of 2014

Tuesday's big flare was an X1.2-class solar event on the scale used to classify sun storms. It occurred at 1:32 p.m. EST (1832 GMT) and came just hours after an M7.2-class flare. Space weather officials at the the Space Weather Prediction Center overseen by NOAA are expecting the flare to spark geomagnetic storms in Earth's magnetic field when a wave of super-hot solar plasma associated with the flare - known as a coronal mass ejection - reaches Earth in the next few days.

[Photos: The Biggest Solar Flares of 2014]

"This is the first significant flare of 2014, and follows on the heels of mid-level flare earlier in the day," NASA spokeswoman Karen Fox of the agency's Goddard Space Flight Center in Greenbelt, Md., wrote in a statement. "Each flare was centered over a different area of a large sunspot group currently situated at the center of the sun, about half way through its 14-day journey across the front of the disk along with the rotation of the sun."

X-class solar flares are the most powerful solar storms on the sun. Mid-level storms are dubbed M-class events and can supercharge Earth's northern lights displays, with weaker C-class flares rounding out the top three.

When aimed directly at Earth, the strongest X-class solar flares can pose a risk to astronauts in orbit and interrupt communications and navigation satellite operations.  [1]

By late Thursday, the comet showed signs that it was still alive and well, or so it seemed.

“It now looks like some chunk of ISON’s nucleus has indeed made it through the solar corona, and re-emerged,” Battams said in an interview with CNN’s Amanda Barnett on Friday. “It’s throwing off dust and (probably) gas, but we don’t know how long it can sustain that.”

He maintained that it would take a few days of observations to get a feel for how ISON made out on its one-way ticket to perihelion.

“Now it has emerged and started to brighten, we need to observe it for a few days to get a feel for its behavior,” Battams noted.

With that being said, today it is clearer that ISON did in fact not survive its ordeal with the sun.

It is evident that the sun’s ferocity was more than the comet could handle, receiving a fatal blow from its perihelion. What is left from the once great and powerful is just a headless dusty ghost of a comet.

When NASA’s Solar Dynamics Observatory caught the last glimpse of ISON fading behind the sun, it was hours before the space agency’s SOHO spacecraft picked it up on the other side. Apart from appearing to survive the encounter, the comet also seemed to make a hairpin turn around the sun, appearing to brighten up and forming a fan-shaped tail.

The reemergence of the comet left many feeling optimistic that ISON would live to fight another day. But by Sunday, Dec 1, experts were painting a pretty clear picture of what really happened. Instead of forming a new zombie-like state, the comet had actually disintegrated and left in its wake just the glowing ghostly remains of a once frozen ball of gas, dust and debris. New satellite imagery does indeed show the comet’s remains are fading fast as it continues its recession from the sun.

“I think for the most part it’s dead,” C. Alex Young, the associate director for science in the heliophysics division at NASA’s Goddard Space Flight Center in Greenbelt, Md, told Kenneth Chang of the NY Times. “The folks are finally pretty confident that’s the case.”

“I really don’t think there’s a whole lot left,” added Battams. “I’m very disappointed for the public, because we’re not going to see this beautiful object in the Northern Hemisphere skies.”

Enthusiastic astronomers were hoping for a spectacular showing of ISON post-perihelion. But it now looks as if there will be no flashy sky show for millions of backyard space enthusiasts.

Experienced astronomers might be able to capture some of the fading ghostly remains in the pre-dawn sky in the coming days and weeks, but there willbe no chance of a naked-eye encounter, according to a statement on spaceweather.com

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http://www.redorbit.com/news/space/1113016710/ison-does-not-survive-perihelion-now-ghost-comet-120213/