Pole Shifts and Magnetic reversal

[Blu]

OK, I posted this link on the Spirituality message board. But it's too good to not have it's own post. You really have to check this out, awesome graphics and very informative page .

Considering that ships, planes and Boy Scouts steer by it, Earth's magnetic field is less reliable than you'd think. Rocks in an ancient lava flow in Oregon suggest that for a brief erratic span about 16 million years ago magnetic north shifted as much as 6 degrees per day. After little more than a week, a compass needle would have pointed toward Mexico City.
The lava catches Earth's magnetic field in the act of reversing itself. Magnetic north heads south, and -- over about 1,000 years -- the field does a complete flip-flop. While the Oregon data is controversial, Earth scientists agree that the geological evidence as a whole -- the "paleomagnetic" record -- proves such reversals happened many times over the past billion years.

"Some reversals occurred within a few 10,000 years of each other," says Los Alamos scientist Gary Glatzmaier, "and there are other periods where no reversals occurred for tens of millions of years." How do these flip-flops happen, and why at such irregular intervals? The geological data, invaluable to show what happened, registers only a mute shrug when it comes to the deeper questions.

For that matter, why is it that instead of quietly fading away, as magnetic fields do when left to their own devices, Earth's magnetic field is still going strong after billions of years? Einstein is said to have considered it one of the most important unsolved problems in physics. With a year of computing on Pittsburgh's CRAY C90, 2,000 hours of processing, Glatzmaier and collaborator Paul Roberts of UCLA took a big step toward some answers. Their numerical model of the electromagnetic, fluid dynamical processes of Earth's interior reproduced key features of the magnetic field over more than 40,000 years of simulated time. To top it off, the computer-generated field reversed itself.

"We weren't expecting it," says Roberts, "and were delighted. This gives us confidence we've built a credible bridge between theory and the paleomagnetic data." Their surprising results, reported as a cover story in Nature (Sept. 21, 1995), provide an inner-Earth view of geomagnetic phenomena that have not been observed or anticipated by theory. Furthermore, the Glatzmaier-Roberts model offers, for the first time, a coherent explanation of magnetic field reversal.


Journey to the Center of the Earth
Roughly speaking, Earth is like a chocolate-covered cherry -- layered, with liquid beneath the surface and a solid inner core. Beneath the planet's relatively thin crust is a thick, solid layer called the mantle. Between the mantle and the inner core is a fluid layer, the outer core. According to generally accepted theory -- the dynamo theory -- interactions between the churning, twisting flow of molten material in the outer core and the magnetic field generate electrical current that, in turn, creates new magnetic energy that sustains the field. "The typical lifetime of a magnetic field like Earth's," says Glatzmaier, "is several tens of thousands of years. The fact that it's existed for billions of years means something must be regenerating it all the time."
How do we know if the dynamo theory is right? To the consternation of our desire to understand what's happening inside the planet we live on, Jules Verne's Journey to the Center of the Earth is still fiction. There's no way to penetrate 4,000 miles to Earth's center, nor to monitor fluid motions or magnetism in the outer core.

The Glatzmaier-Roberts computational model may be the next best thing to a guided tour of inner Earth. While other models have given good clues that theory is on track, they have been limited by a two-dimensional approach that required simplifying assumptions. Roberts and Glatzmaier set out to implement a fully three-dimensional model, based on a computer program Glatzmaier developed over many years, that would allow the complex feedbacks between fluid motion and the magnetic field to evolve on their own -- in other words, to be solved "self consistently."

Simulated three-dimensional structure of Earth's magnetic field, with inward (blue) and outward (yellow) directed field lines. Field lines extend two Earth radii from the core. The location of the core-mantle boundary is evident where the structure becomes complex.
Their objectives, in retrospect, were modest. "Mainly," says Roberts, "we wanted to get a geomagnetic field that would maintain itself longer than the decay time. No one's ever done that in a self-consistent manner." After nearly a year running almost daily, as allocated computing time was about to expire, the model produced its Eureka moment.

By itself, the reversal is strong confirmation of the model, and other details -- magnitude and structure of the field -- also agree well with surface features of Earth's field. The simulation also offers precious insight into the dynamics that sustain the magnetic field and generate reversals. Contrary to what anyone guessed till now, the model shows that in the inner core the magnetic field has an opposite polarity from the outer core, and this stabilizes the field against a tendency to reverse more frequently.

"No one even dreamed about this," says Glatzmaier. "That's the nice thing about a supercomputer. You can just let it do its thing, solve these equations over and over -- a large set of variables affecting each other with nonlinear feedback, very hard to figure out. It's a beautiful problem for a supercomputer, and it's really exciting to see this structure and dynamics that no one imagined."

Reversal of Earth's Magnetic Field
Earth's magnetic field evolving for about 9,000 years before, during and after the simulated reversal. The outer circle indicates the fluid outer core boundary; the inner circle, the solid inner core. The left hemisphere shows magnetic field contours directed clockwise (green) and counterclockwise (yellow). The right hemisphere shows contours directed westward (blue) and eastward (red), out of and into the plane of the paper.

The left hemisphere shows that the field penetrating the inner core is opposed in polarity to the outer core, a feature completely unanticipated by theory. "The outer core polarity," explains Glatzmaier, "is continually trying to invade the inner core. Only when the whole field almost decays away, however [middle], does it finally have a chance to diffuse in. Once it does, the opposite polarity gets established. The inner core polarity is the stabilizing force, like an anchor, the slowest thing that can change."


Animation
1.62 MB
At about 36,000 years into the simulation the magnetic field reversed its dipole polarity over a period of only 1200 years. The image below is from an animated sequence showing how the field's structure changed.

Click on the image to the left to download the animation (1.62 MB).




--------------------------------------------------------------------------------
Researchers: Gary Glatzmaier, Los Alamos National Laboratory.
Paul Roberts, University of California-Los Angeles.
Hardware: Cray C90
Software: User-developed code.
Keywords: magnetic field reversal, lava, paleomagnetic record, geomagnetic phenomena, dynamo theory, outer core, inner core, polarity, Earth.

Related Material on the Web:
"Will Compasses Point South?" New York Times 13 July 2004.
Los Alamos National Laboratory
Generation and Evolution of the Earth's Magnetic Field further information on the research by Gary Glatzmaier
Geodynamo -- The first self-consistent 3D numercial simulation of the "geodynamo".
Projects in Scientific Computing, PSC's annual research report.
PSC Scientific Visualisation Animations and Images

References, Acknowledgements & Credits
www.psc.edu/science/Glatzmaier/glatzmaier.html

[Blu]

To really appreciate this article you have to go to the page and see the graphics.




On January 6, 1997, the sun burped, in a manner of speaking, and a billion-ton bubble of hot gas came blasting toward Earth at about a million miles an hour. Four days later, pushing a pileup of solar magnetic field called a magnetic cloud, the bubble rammed the nose of Earth's magnetic field, and while most of us were blissfully unaware, the resulting magnetic storm put on a show for space physicists.


This POLAR satellite view of the Arctic shows an ultraviolet image of electromagnetic radiation from the auroral oval during the January 1997 magnetic storm. Image provided courtesy of Marshall Space Flight Center.
Download larger version (277KB) of this image.
A satellite orbiting 350 miles above the Earth recorded an electrical burst 10,000 times normal intensity, and the high levels lasted a week. On January 11, the dense trailing edge of the bubble delivered a parting shot to the magnetosphere — the outer boundary of Earth's magnetism, and the energy dissipation in the auroras over the North and South Poles climbed to 1,400 gigawatts, nearly double U.S. power-generating capacity.

It was an impressive display of space weather, and it demonstrated how these gusts of solar wind — the stream of charged particles from the sun — can play havoc with our information age infrastructure. On January 11, loss of radio contact grounded a plane trying to take off from Halley Bay Station, Anarctica, and a $200 million communications satellite, Telstar 401, fell silent, forcing network broadcasts to switch to another satellite.

Severe magnetic storms have occurred before. A March 1989 storm blacked out Hydro Quebec, a Canadian utility, and the drain on generating capacity threatened to knock out the northeast U.S. power grid. January 1997 was the first time, however, that a fleet of observational satellites was in place to capture data from such an event, and by January 17, less than a week after the solar bubble passed, Chuck Goodrich and colleagues at the University of Maryland Space and Plasma Physics Group (SPP) were using this data in an unprecedented computational study.

"This event had intense scientific interest and news coverage," says Goodrich. "NASA asked us to simulate it, and thanks to PSC we were able to provide video animations on very short notice." Running on four processors of the CRAY C90 at Pittsburgh Supercomputing Center, Goodrich and his SPP colleagues, John Lyon of Dartmouth, Dennis Papadopoulos and Mike Wiltberger used their 3D magneto-hydrodynamics software to simulate the entire storm, from the arrival of the shock front preceding the bubble through the next day and a half, over 45 hours of storm time. "In space science," says Goodrich, "this was a simulation project of unprecedented proportion." Within a week, they had results: seven gigabytes of data, and visualizations that offer a global view of a geomagnetic storm unobtainable any other way.



Earth's Magnetosphere
The top image shows the "relaxed" magnetosphere three hours prior to the onset of the January 10, 1997 magnetic storm, solar wind arriving from the left. The bottom image shows the magnetosphere three hours later. The translucent surface represents the shape and extent of Earth's magnetic field. The colormap indicates plasma density and shows the sunward shock wave around the Earth.
Click on the images to download a larger version.
The Big Picture
First observed in the early 1970s, these eruptions of solar gas occur as often as once a day and the frequency may increase as the year 2000 peak of the 11-year solar cycle approaches. Even the most severe solar gusts present no known health hazard, since Earth's magnetosphere serves as a protective barrier, deflecting the mass flow. But some of the flow energy transmits through the magnetosphere and shows up as bursts of electromagnetism in the ionosphere, hence the Northern and Southern lights, and the potential to seriously disrupt our power supply and communications systems.

The advance guard for detecting blasts of solar wind headed our way was two satellites, SOHO and WIND, that hover about 600,000 miles out on the sunward side of Earth — revolving around the point in space where the Earth's gravity and the sun's are equal. Earth-orbit satellities closer in gather data on near-Earth effects.

While the information from these satellites is invaluable, it represents pinpoints in a huge volume. "You often don't know how what happens here relates to what happens over there," says Goodrich. "You may have readings from several points at the same time, but you don't know what happens in between." With supercomputing, the SPP group connects the dots and produces a big picture view.

"The basic question in magnetospheric physics," says Goodrich, "is how energy from the plasma flow past the Earth penetrates the magnetosphere and gets absorbed in the inner atmosphere. Until recently, we knew observational effects, but we didn't know the basic physics behind them. We have theories, but it's been impossible to check them. Simulations help us understand the detailed physics."

The SPP numerical model simulates a solar storm impacting the magnetosphere and transferring energy through it to Earth's ionosphere. SPP used data from WIND and SOHO for the flow and magnetic field of the January 1997 incoming gust of solar wind. A set of magneto-hydrodynamic equations then takes over and calculates effects throughout the magnetospheric volume, represented as a grid in the stretched-out spherical shape of the magnetosphere. Earth's ionosphere is a lower boundary of the model volume, from which the simulation maps electrical current and velocity through the ionosphere. "From that model," says Goodrich, "we can predict ground currents and magnetometer measurements on Earth, and what's floating onto the electric power lines."

The Unforeseen Effect of Plasma Density



These frames from the SPP visualization show plasma density (indicated by color) in the plane of Earth's equator in the early hours of January 11, when the dense trailing edge of the solar bubble strikes the leading-edge of Earth's magnetosphere. The black circle represents geosynchronous orbit, with satellite positions indicated. Earth is magnified by a factor of two for clarity.
Click on the images to download a larger (200KB) version.
The results of the SPP simulations of the January 1997 storm agree well in key details with Earth-orbit satellite data, confirming basic accuracy of the model. The simulation shows bursts of released energy in the ionosphere happening close in time to when such bursts were recorded at near-Earth satellites. Similarly, the simulation shows energy entering the ionosphere in the same place shown in ultraviolet images from POLAR, a satellite orbiting above the Arctic.

The simulation shows the first significant energy transfer — called a magnetic substorm — occurring on January 10 after a southward turn in orientation of the solar wind magnetic field. Physicists have postulated — and studies have confirmed — that energy transfer happens predominantly when this occurs, since southward orientation of the solar field is opposite to the northward orientation of Earth's magnetosphere. The opposed polarities, in theory, allow the magnetic field lines to connect and energy to flow across the connections.

The simulations confirm this view, and offer added insight. When the magnetic cloud in front of the gas bubble arrived, it brought with it an abrupt southward shift and an increase in the strength of the solar magnetic field, initiating a prolonged substorm. Late on January 10 through early January 11, the field direction turned gradually northward, closing off the energy transfer.

The simulation showed, however, that within the period of southward orientation the rise and fall of ionospheric activity correlated with solar wind density. This was a new finding. "Prior studies of substorm triggering," says Goodrich, "focused on the northward turning of the magnetic field." The simulation shows lack of intense activity for almost two hours after the magnetic cloud arrives. Although it brought a strong southward shift of the magnetic field, the plasma density was unusually low. Subsequent bursts of energy transfer correspond to arrival of denser gas behind the magnetic cloud.

Goodrich and his colleagues surmise that prior studies may not have reflected the extreme southward field orientation that persisted during the January 10 magnetic cloud: "We suspect that the large amount of coupling between the solar wind and the magnetosphere during the southward phase of the cloud allowed a significant fraction of solar wind kinetic energy to enter the magnetosphere." The SPP group plans to investigate this hypothesis in future work.

The January storm was not the biggest of its kind, notes Goodrich, but its significance lies in being the first intense magnetic storm followed in its entirety, from the sun to the ionosphere. "This is the first one we've been able to track as a full event," says Goodrich, "and the animations had a big impact. Space physics deals with invisible fields and particles, and an image carries great weight. Without centers like PSC, we wouldn't be able to do this."

Excerpt from the video animation of CME impact on our magnetosphere (4.2MB). The full animation can be found at the University of Maryland, Space and Plasma Physics Group Website.



www.psc.edu/science/Goodrich/goodrich.html

[Blu]

I wish I had known Science was this cool a long time ago!
A Seismic Adventure
There's a giant crystal buried deep within the Earth, at the very center, more than 3,000 miles down. It may sound like the latest fantasy adventure game or a new Indiana Jones movie, but it happens to be what scientists discovered in 1995 with a sophisticated computer model of Earth's inner core. This remarkable finding, which offers plausible solutions to some perplexing geophysical puzzles, is transforming what Earth scientists think about the most remote part of our planet.
"To understand what's deep in the Earth is a great challenge," says geophysicist Lars Stixrude. "Drill holes go down only 12 kilometers, about 0.2 percent of the Earth's radius. Most of the planet is totally inaccessible to direct observation." What scientists have pieced together comes primarily from seismic data. When shock waves from earthquakes ripple through the planet, they are detected by sensitive instruments at many locations on the surface. The record of these vibrations reveals variations in their path and speed to scientists who can then draw inferences about the planet's inner structure. This work has added much knowledge over the last ten years, including a puzzling observation: Seismic waves travel faster north-south than east-west, about four seconds faster pole-to-pole than through the equator.

This finding, confirmed only within the past two years, quickly led to the conclusion that Earth's solid-iron inner core is "anisotropic" -- it has a directional quality, a texture similar to the grain in wood, that allows sound waves to go faster when they travel in a certain direction. What, exactly, is the nature of this inner-core texture? To this question, the seismic data responds with sphinx-like silence. "The problem," says Ronald Cohen of the Carnegie Institution of Washington, "is then we're stymied. We know there's some kind of structure, the data tells us that, but we don't know what it is. If we knew the sound velocities in iron at the pressure and temperature of the inner core, we could get somewhere." To remedy this lack of information, Stixrude and Cohen turned to the CRAY C90 at Pittsburgh Supercomputing Center.

Earth's layered structure -- a relatively thin crust of mobile plates, a solid mantle with gradual overturning movement, and the outer and inner core of molten and solid iron.

Getting to the Core
Don't believe Jules Verne. The center of the Earth is not a nice place to visit, unless you like hanging out in a blast furnace. The outer core of the Earth, about two-thirds of the way to the center, is molten iron. Deeper yet, at the inner core, the pressure is so great -- 3.5 million times surface pressure -- that iron solidifies, even though the temperature is believed to exceed 11,000 degrees Fahrenheit, hotter than the surface of the sun.
Despite rapid advances in high-pressure laboratory techniques, it's not yet possible to duplicate these conditions experimentally, and until Stixrude and Cohen's work, scientists could at best make educated guesses about iron's atom-to-atom architecture -- its crystal structure -- at the extremes that prevail in the inner core. Using a quantum-based approach called density-functional theory, Stixrude and Cohen set out to do better than an educated guess. With recent improvements in numerical techniques, density-functional theory had predicted iron's properties at low pressure with high accuracy, leading the researchers to believe that with supercomputing they could, in effect, reach 3,000 miles down into the inner core and pull out what they needed.

Three crystal structures of iron. Yellow lines show bonds between iron atoms.

Rethinking Inner Earth
On Earth's surface, iron comes in three flavors, standard crystalline forms known to scientists as body-centered cubic (bcc), face-centered cubic (fcc) and hexagonal close-packed (hcp). Working with these three structures as their only input, Stixrude and Cohen carried out an extensive study -- more than 200 separate calculations over two years -- to determine iron's quantum-mechanical properties over a range of high pressures. "Without access to the C90," says Stixrude, "this work would have taken so long it wouldn't have been done."

Prevalent opinion before these calculations held that iron's crystal structure in the inner core was bcc. To the contrary, the calculations showed, bcc iron is unstable at high pressure and not likely to exist in the inner core. For the other two candidates, fcc and hcp, Stixrude and Cohen found that both can exist at high pressure and both would be directional (anisotropic) in how they transmit sound. Hcp iron, however, gives a better fit with the seismic data. All this was new information, but even more surprising was this: To fit the observed anisotropy, the grain-like texture of the inner core had to be much more pronounced than previously thought.

"Hexagonal crystals have a unique directionality," says Stixrude, "which must be aligned and oriented with Earth's spin axis for every crystal in the inner core." This led Stixrude and Cohen to try a computational experiment. If all the crystals must point in the same direction, why not one big crystal? The results, published in Science, offer the simplest, most convincing explanation yet put forward for the observed seismic data and have stirred new thinking about the inner core.

Could an iron ball 1,500 miles across be a single crystal? Unheard of until this work, the idea has prompted realization that the temperature-pressure extremes of the inner core offer ideal conditions for crystal growth. Several high-pressure laboratories have experiments planned to test these results. A strongly oriented inner core could also explain anomalies of Earth's magnetic field, such as tilted field lines near the equator. "To do these esoteric quantum calculations," says Stixrude, "solutions which you can get only with a supercomputer, and get results you can compare directly with messy observations of nature and help explain them -- this has been very exciting."


Researchers: Ronald Cohen and Lars Stixrude, Carnegie Institution of Washington.

www.psc.edu/science/Cohen_Stix/cohen_stix.html