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Blobrana


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RE: Magnetic Pole
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Something beneath the surface is changing Earth's protective magnetic field, which may leave satellites and other space assets vulnerable to high-energy radiation.
The gradual weakening of the overall magnetic field can take hundreds and even thousands of years. But smaller, more rapid fluctuations within months may leave satellites unprotected and catch scientists off guard, new research finds.
A new model uses satellite data from the past nine years to show how sudden fluid motions within the Earth's core can alter the magnetic envelope around our planet. This represents the first time that researchers have been able to detect such rapid magnetic field changes taking place over just a few months.

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Blobrana


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Magnetic field vortices
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UC Davis researchers studying cores of sediment collected 40 years ago have found evidence for magnetic field vortices in the Earth's core beneath the South Pole. The results contrast with earlier studies at lower latitudes, and could lead to a better understanding of processes in the core.
The results came from a seabed sediment core collected by the U.S. Navy in the Antarctic Ross Sea in 1968 as part of Operation Deep Freeze. Samples from the core, covering almost 2.5 million years of the Earth's history, were stored at the Antarctic Marine Geology Research Facility in Tallahassee, Fla., before being re-discovered by Ken Verosub, professor of geology at UC Davis, who brought them back to Davis for magnetic analysis.
Exposed rock on land is weathered into fine grains that are washed out to sea and settle to the bottom. If the grains are magnetic, they will tend to align themselves with the Earth's magnetic field as they settle through the water column.

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Blobrana


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Magnetic Field Reversals
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Compasses could start pointing south soon — as in mere thousands of years — according to new simulations of Earth's internal magnetic field.
Mathematical models indicate that the more tidily the undulations in Earth's magnetic field align with the equator, the more prone the field is to reversing its polarity.
Such a reversal would involve a fading out in the magnetic field and then a restarting, causing compass needles to swing south.

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Blobrana


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A new analysis of computer simulations of Earth's magnetic field suggests that its behaviour was different early in Earth's history, resulting in greater stability and fewer reversals of the magnetic field. The findings by researchers at the University of California, Santa Cruz, are helping to reconcile the geologic record of magnetic field reversals with the current understanding of how the Earth's core generates the planet's magnetic field.

Robert Coe and Gary Glatzmaier, both professors of Earth sciences at UCSC, combine studies of the paleomagnetic records preserved in rocks with complex computer models of the "geodynamo" that generates the magnetic field. Working together, they are gaining new insights into the effects on the magnetic field of processes occurring deep within the Earth.

Coe will presented their findings last week at the Fall Meeting of the American Geophysical Union in San Francisco (session GP23B, talk #8, on Tuesday, December 6, at 3:25 p.m.)
The magnetic field arises as a result of interactions in the Earth's iron-rich core, which consists of a solid inner core and a fluid outer core. The flow of heat from the core drives fluid motions in the outer core that produce an electric current and generate the magnetic field.
On human timescales, the magnetic field reliably aligns compass needles, helps animals navigate, and deflects some of the Sun's radiation. But on geologic timescales, it is far from stable--weakening, strengthening, and sometimes even reversing itself. A reversal of the magnetic field would cause the needles on compasses to point south instead of north.
In the last 15 million years (a relatively brief interval in Earth's history), the magnetic field has reversed roughly four to five times every million years. But records from the ocean floor indicate that reversal rates have been much lower at various times in the past. In fact, during a period that began 120 million years ago, there are no records of any magnetic reversals for nearly 35 million years.

The geodynamo simulations show that the shape of the magnetic field may be an important factor controlling reversal rates. The symmetry and stability of the simulated field varies depending on the pattern of heat flow imposed at the core-mantle boundary. When the field is symmetrical in Northern and Southern Hemispheres, the simulations show frequent reversals. Conversely, when the field is strongly antisymmetric, with the Northern and Southern Hemispheres displaying opposite features, it reverses infrequently or not at all.
This finding is consistent with studies by other researchers of the paleomagnetic record of Earth's magnetic field during the 35 million years with no reversals, indicating that it was much more antisymmetric then than it is today.
The simulation that produced the most antisymmetric and most stable field is one with an inner core only one-quarter of its current size. Scientists believe that as the core cools, iron crystallises out of the fluid outer core onto the solid inner core, causing the inner core to grow slowly over time. Thus, this simulation mimics conditions deep in Earth's past and predicts that reversals would have occurred much less frequently then than now. A survey of the sparse literature on the magnetic field 2 billion and more years ago suggests that this may well have been the case.

"The data are consistent with simulations showing that field symmetry influences reversal rate" - Robert Coe .

The Earth's magnetic field has been weakening for 2,000 years, and that trend continues today, leading some to worry that it may be heading for a reversal. Although the idea of an impending magnetic field reversal has captured the imaginations of writers and television producers, Coe said he thinks that a reversal would be unlikely to produce a catastrophic effect. Furthermore, reversals take thousands of years, and the field has decreased many times in the past and not reversed.

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Blobrana


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Magnetic Pole
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Earth's north magnetic pole is drifting away from North America and toward Siberia .
After some 400 years of relative stability, Earth's North Magnetic Pole has moved nearly 1,100 kilometres out into the Arctic Ocean during the last century.

The shift could mean auroras might be more visible in more southerly areas of Siberia and Europe.

The magnetic poles are part of the magnetic field generated by liquid iron in Earth's core and are different from the geographic poles, the surface points marking the axis of the planet's rotation.
Surprisingly rapid movement of the magnetic pole doesn't necessarily mean that our planet is going through a large-scale change that would result in the reversal of the Earth's magnetic field
Scientists have long known that magnetic poles migrate and in rare cases, swap places. Exactly why this happens is a mystery.

"This may be part of a normal oscillation and it will eventually migrate back toward Canada. There is a lot of variability in its movement" - Joseph Stoner, a paleomagnetist at Oregon State University, College of Oceanic and Atmospheric Sciences.

Previous studies have shown that the strength of the Earth's magnetic shield has decreased 10 percent over the past 150 years. During the same period, the north magnetic pole wandered about 685 miles out into the Arctic, according to a new analysis by Stoner.
Calculations of the North Magnetic Pole's location from historical records goes back only about 400 years, while polar observations trace back to John Ross in 1838 at the west coast of Boothia Peninsula. To track its history beyond that, scientists have to dig into the Earth to look for clues.
The rate of the magnetic pole's movement has increased in the last century compared to fairly steady movement in the previous four centuries.

If north magnetic pole shifts into Siberia, the Northern Lights, which occur when charged particles streaming away from the sun interact with different gases in Earth's atmosphere, may become stronger there. Radiation influx is associated with the magnetic field, and charged particles streaming down through the atmosphere can affect airplane flights and telecommunications.

The north magnetic pole was first discovered in 1831 and when it was revisited in 1904, explorers found that the pole had moved 31 miles.
For centuries, navigators using compasses had to learn to deal with the difference between magnetic and geographic north. A compass needle points to the north magnetic pole, not the geographic North Pole. For example, a compass reading of north in Oregon is about 17 degrees east of geographic north.

"There is a lot of variability in the polar motion, but it isn't something that occurs often. There appears to be a 'jerk' of the magnetic field that takes place every 500 years or so. The bottom line is that geomagnetic changes can be a lot more abrupt than we ever thought"- Joseph Stoner.

Stoner and his colleagues have examined the sediment record from several Arctic lakes. These sediments – magnetic particles called magnetite – record the Earth's magnetic field at the time they were deposited. Using carbon dating and other technologies – including layer counting – the scientists can determine approximately when the sediments were deposited and track changes in the magnetic field.

They found that the north magnetic field shifted significantly in the last thousand years. It generally migrated between northern Canada and Siberia, but it sometimes moved in other directions, too.
The Earth last went through a magnetic reversal some 780,000 years ago. These episodic reversals, in which south becomes north and vice versa, take thousands of years and are the result of complex changes in the Earth's outer core. Liquid iron within the core generates the magnetic field that blankets the planet.

In their research, funded by the National Science Foundation, Stoner and his colleagues took core samples from several lakes, but focused on Sawtooth Lake and Murray Lake on Ellesmere Island in the Canadian Arctic. These lakes, about 40 to 80 meters deep, are covered by 2-3 meters of ice. The researchers drill through the ice, extend their corer down through the water, and retrieve sediment cores about five meters deep from the bottom of the lakes. The 5-meter core samples provide sediments deposited up to about 5,000 years ago. Below that is bedrock, scoured clean by ice about 7,000 to 8,000 years ago.

"The conditions there give us nice age control. One of the problems with tracking the movement of the North Magnetic Pole has been tying the changes in the magnetic field to time. There just hasn't been very good time constraint. But these sediments provide a reliable and reasonably tight timeline, having consistently been laid down at the rate of about one millimetre a year in annual layers. We're trying to get the chronology down to a decadal scale or better"- Joseph Stoner.

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