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Posts: 131433
Date:
Geomagnetic field reversal
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Title: What happens when the geomagnetic field reverses?
Authors: Joseph F. Lemaire, Fred Singer

During geomagnetic field reversals the radiation belt high-energy proton populations become depleted. Their energy spectra become softer, with the trapped particles of highest energies being lost first, and eventually recovering after a field reversal. The radiation belts rebuild in a dynamical way with the energy spectra flattening on the average during the course of many millennia, but without ever reaching complete steady state equilibrium between successive geomagnetic storm events determined by southward turnings of the IMF orientation. Considering that the entry of galactic cosmic rays and the solar energetic particles with energies above a given threshold are strongly controlled by the intensity of the northward component of the interplanetary magnetic field, we speculate that at earlier epochs when the geomagnetic dipole was reversed, the entry of these energetic particles into the geomagnetic field was facilitated when the interplanetary magnetic field was directed northward. Unlike in other complementary work where intensive numerical simulations have been used, our demonstration is based on a simple analytical extension of Stormer's theory. The access of GCR and SEP beyond geomagnetic cut-off latitudes is enhanced during epochs when the Earth's magnetic dipole is reduced, as already demonstrated earlier.

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Posts: 131433
Date:
North Magnetic Pole
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Sir James Clark Ross (15 April 1800 - 3 April 1862), was a British naval officer and explorer. He explored the Arctic with his uncle Sir John Ross and Sir William Parry, and later led his own expedition to Antarctica.
He located the position of the North Magnetic Pole on 1 June 1831 on the Boothia Peninsula in the far north of Canada.

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Magnetic Pole Shifts 1590-2010



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Posts: 131433
Date:
Magnetic South Pole
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Journey Under Way to Track the Magnetic South Pole

Two scientists from New Zealand will travel to Antarctica on December 28 in a quest to continue a 100-year-long record of Earth's magnetic field: a record begun by British explorer Robert Scott at the start of his ill-fated expedition to the geographic south pole
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Posts: 131433
Date:
Magnetic Pole Reversal
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Magnetic Pole Reversal Happens All The (Geologic) Time

Scientists understand that Earth's magnetic field has flipped its polarity many times over the millennia. In other words, if you were alive about 800,000 years ago, and facing what we call north with a magnetic compass in your hand, the needle would point to 'south.' This is because a magnetic compass is calibrated based on Earth's poles. The N-S markings of a compass would be 180 degrees wrong if the polarity of today's magnetic field were reversed. Many doomsday theorists have tried to take this natural geological occurrence and suggest it could lead to Earth's destruction. But would there be any dramatic effects? The answer, from the geologic and fossil records we have from hundreds of past magnetic polarity reversals, seems to be 'no.'
Reversals are the rule, not the exception. Earth has settled in the last 20 million years into a pattern of a pole reversal about every 200,000 to 300,000 years, although it has been more than twice that long since the last reversal. A reversal happens over hundreds or thousands of years, and it is not exactly a clean back flip. Magnetic fields morph and push and pull at one another, with multiple poles emerging at odd latitudes throughout the process. Scientists estimate reversals have happened at least hundreds of times over the past three billion years. And while reversals have happened more frequently in "recent" years, when dinosaurs walked Earth a reversal was more likely to happen only about every one million years.

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Posts: 131433
Date:
RE: Magnetic Pole
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The north magnetic pole (NMP), also known as the dip pole, is the point on Earth where the planet's magnetic field points straight down into the ground. Scottish explorer James Clark Ross first located the NMP in 1831 on the Boothia Peninsula in what is now northern Canada, and with the planting of a flag claimed it for Great Britain.
But the NMP drifts from year to year as geophysical processes within Earth change. For more than 150 years after Ross's measurement its movement was gradual, generally less than 15 kilometres per year. But then, in the 1990s, it picked up speed in a big way, bolting north-northwest into the Arctic Ocean at more than 55 kilometres per year. If it keeps going it could pass the geographic north pole in a decade or so and carry on toward Siberia. But why?

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Some 16 million years ago, north became south in a matter of years. Such fast flips are impossible, according to models of the Earth's core, but this is now the second time that evidence has been found.
The magnetic poles swap every 300,000 years, a process that normally takes up to 5000 years. In 1995 an ancient lava flow with an unusual magnetic pattern was discovered in Oregon. It suggested that the field at the time was moving by 6 degrees a day - at least 10,000 times faster than usual.

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Posts: 131433
Date:
Magnetic Field Reversal
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Pourquoi le champ magnétique terrestre s'est-il inversé au cours de l'histoire de la Terre, pointant alternativement vers le nord ou le sud géographique ? Si l'on sait que l'explication réside dans les mouvements qui animent le noyau liquide de la Terre, les mécanismes en jeux restent mal compris. Dans une publication qui vient de paraître dans Physical Review Letters des chercheurs du Laboratoire de physique statistique (ENS, CNRS) et de l'Institut de Physique du Globe de Paris (INSU-CNRS, Paris Diderot) proposent que les renversements se produisent lorsque des fluctuations brisent la symétrie de l'écoulement dans le noyau liquide et qu'un couplage fort entre deux modes du champ magnétique (bipolaire et quadripolaire) se produit.

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Posts: 131433
Date:
Earth's magnetic field
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Earth's magnetic field, which shields our planet from particles streaming outward from the Sun, often develops two holes that allow the largest leaks, according to researchers sponsored by NASA and the National Science Foundation.

"The discovery overturns a long-standing belief about how and when most of the solar particles penetrate Earth's magnetic field, and could be used to predict when solar storms will be severe. Based on these results, we expect more severe storms during the upcoming solar cycle" - Vassilis Angelopoulos of the University of California, Los Angeles, Principal Investigator for NASA's THEMIS mission (Time History of Events and Macroscale Interactions during Substorms). THEMIS was used to discover the size of the leak.

Earth's magnetic field acts as a shield against the bombardment of particles continuously streaming from the sun. Because the solar particles (ions and electrons) are electrically charged, they feel magnetic forces and most are deflected by our planet's magnetic field. However, our magnetic field is a leaky shield and the number of particles breaching this shield depends on the orientation of the sun's magnetic field. It had been thought that when the sun's magnetic field is aligned with that of the Earth, the door is shut and that few if any solar particles enter Earth's magnetic shield. The door was thought to open up when the solar magnetic field direction points opposite to Earth's field, leading to more solar particles inside the shield.
Surprisingly, recent observations by the THEMIS spacecraft fleet demonstrate that the opposite is true.

"Twenty times more solar particles cross the Earth's leaky magnetic shield when the sun's magnetic field is aligned with that of the Earth compared to when the two magnetic fields are oppositely directed" - Marit Oieroset of the University of California, Berkeley, lead author of one of two papers on this research, published May 2008 in Geophysical Research Letters.

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Posts: 131433
Date:
Earth’s magnetic-field flipping
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Geophysicists in the US are proposing a new magnetic field generated in the Earths core, the existence of which could help us understand why our planets magnetic moment has flipped several times in the past.
By measuring ancient field patterns frozen into the volcanic rocks of West Eifel in Germany and Tahiti in French Polynesia, Kenneth Hoffman of California Polytechnic University and Brad Singer of the University of WisconsinMadison have recorded the first data to suggest that the Earths dipolar magnetic field is accompanied by a second magnetic field with a distinct origin in the Earths core.

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Posts: 131433
Date:
RE: Magnetic Pole
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Ancient lava flows are guiding a better understanding of what generates and controls the Earth's magnetic field - and what may drive it to occasionally reverse direction.

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