Posts Tagged ‘Magnetic field

Planetary Poles and Magnetic Fields

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Dr Meghan Gray chats about magnetic fields and the Earth’s changeable poles.

Written by physicsgg

May 13, 2019 at 6:40 pm

Posted in GEOLOGY

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Earth’s magnetic field could flip within a human lifetime

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The ‘north pole’ — that is, the direction of magnetic north — was reversed a million years ago. This map shows how, starting about 789,000 years ago, the north pole wandered around Antarctica for several thousand years before flipping 786,000 years ago to the orientation we know today, with the pole somewhere in the Arctic.

The ‘north pole’ — that is, the direction of magnetic north — was reversed a million years ago. This map shows how, starting about 789,000 years ago, the north pole wandered around Antarctica for several thousand years before flipping 786,000 years ago to the orientation we know today, with the pole somewhere in the Arctic.

By Robert Sanders
BERKELEY — Imagine the world waking up one morning to discover that all compasses pointed south instead of north.

It’s not as bizarre as it sounds. Earth’s magnetic field has flipped – though not overnight – many times throughout the planet’s history. Its dipole magnetic field, like that of a bar magnet, remains about the same intensity for thousands to millions of years, but for incompletely known reasons it occasionally weakens and, presumably over a few thousand years, reverses direction.

Now, a new study by a team of scientists from Italy, France, Columbia University and the University of California, Berkeley, demonstrates that the last magnetic reversal 786,000 years ago actually happened very quickly, in less than 100 years – roughly a human lifetime.

“It’s amazing how rapidly we see that reversal,” said UC Berkeley graduate student Courtney Sprain. “The paleomagnetic data are very well done. This is one of the best records we have so far of what happens during a reversal and how quickly these reversals can happen.”

Sprain and Paul Renne, director of the Berkeley Geochronology Center and a UC Berkeley professor-in- residence of earth and planetary science, are coauthors of the study, which will be published in the November issue of Geophysical Journal International and is now available online. Read the rest of this entry »

Written by physicsgg

October 16, 2014 at 11:25 am

Posted in GEOLOGY

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Earth’s magnetic shield behaves like a sieve

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When the Earth’s magnetic field and the interplanetary magnetic field are aligned, for example in a northward orientation as indicated by the white arrow in this figure, Kelvin–Helmholtz waves are generated at low (equatorial) latitudes. (Courtesy: ESA/AOES Medialab)

The Earth’s magnetic field is more permeable than previously thought, according to researchers analysing data from the European Space Agency’s Cluster mission. The findings have implications for modelling the dangers posed by space weather and could also help us better understand the magnetic environments around Jupiter and Saturn.
The Cluster mission, launched in 2000, comprises four identical satellites flying in a tetrahedral formation in close proximity to Earth. With highly elliptical orbits, the satellites are able to sweep in and out of the Earth’s magnetic environment, building up a 3D picture of interactions between the solar wind and our planet. The solar wind is a stream of charged particles from the outer layers of the Sun blowing into the solar system. The Earth’s magnetic field is thought to form a protective barrier against it.
It is well known, however, that if the magnetic field of the incoming solar wind has the opposite orientation to the Earth’s magnetic field, then the field lines can break and join up again in a process known as “magnetic reconnection”. This process allows the plasma from the solar wind to breach the boundary of the Earth’s magnetic field – the magnetopause – where it can then potentially reach our planet…..
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Written by physicsgg

November 5, 2012 at 5:16 pm

Posted in SPACE

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New chemical bonds possible in extreme magnetic fields

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Could helium molecules form in very high magnetic fields? (Courtesy: NASA)

In the extreme magnetic fields of white dwarves and neutron stars, a third type of chemical bonding can occur. That is the finding of theoretical chemists in Norway, who have used computer simulations to show that as-yet-unseen molecules could form in magnetic fields much higher than those created here on Earth.
High-school chemistry students are taught that there are two types of chemical bond – ionic bonds, in which one atom donates an electron to another atom; and covalent bonds, in which the electrons are shared. In fact, real chemical bonds usually fall somewhere in between.
When two atoms come together, their atomic orbitals combine to form molecular orbitals. For each two atomic orbitals combined, two molecular orbitals are formed. One of these is lower in energy than either atomic orbital and is called the bonding orbital. The other “anti-bonding” orbital is higher in energy than either atomic orbital. Whether or not the atoms will actually bond is determined by whether the total energy of the electrons in the molecular orbitals is lower than the total energy of the electrons in the original atomic orbitals. If it is, bond formation will be energetically favoured and the bond will be formed.

Bonding and anti-bonding

The Pauli exclusion principle forbids a single orbital from holding more than two electrons (it can hold two if they have opposite spins). If the atomic orbital of each atom contained just one electron, both can go into the bonding orbital when the orbitals combine. Both electrons are therefore lowered in energy and the bond formation is energetically favoured. But if the atomic orbitals contained two electrons each, two of the four electrons would have to go into the anti-bonding molecular orbital. Overall, therefore, two electrons would have their energy lowered by bond formation, while two electrons would have their energy raised.
Under normal circumstances, the anti-bonding orbital is always raised in energy farther above the energy of the higher-energy atomic orbital than the bonding orbital is lowered below the energy of the lower-energy atomic orbital. This means that a chemical bond with both its bonding and its anti-bonding orbitals full would always have a higher energy than the atomic orbitals from which it would be formed. Such a bond would therefore not form. This is why noble-gas atoms, which have full outer atomic orbitals, almost never form molecules on Earth.
But now Kai Lange and colleagues at the University of Oslo have used a computer program developed by their group called LONDON to show this is not always true elsewhere. LONDON creates mathematical models of molecular orbitals under the influence of magnetic fields of about 105 T. This is much stronger than the 30–40 T fields that can be made in laboratories and that have little effect on chemical bonds.

Changing the rules

Large fields could be relevant to those studying astronomical objects such as white dwarves – where magnetic fields can reach 105 T – and neutron stars, where fields could be as high as 1010 T. Under such conditions, the team has shown that the rules of bonding change. In particular, the anti-bonding orbital is lowered in energy when a diatomic molecule is subjected to a strong perpendicular magnetic field. Molecules with full bonding and anti-bonding orbitals, such as diatomic helium, can still be energetically favoured.
Team leader Trygve Helgaker explains the sophistication of LONDON enabled the group to perform calculations that others have found impossible. “We can do accurate calculations with all orientations of the molecule to the magnetic field,” he says. “People have done the same kinds of electronic-structure calculations before, but I believe their calculations were limited to the situation where the field is parallel to the molecular axis.”
The research is published in Science; in an accompanying commentary, Peter Schmelcher of the Institute for Laser Physics at the University of Hamburg, Germany, said “Atoms, molecules and condensed-matter systems exposed to strong magnetic fields represent a fascinating topic, and this work has added a key bonding mechanism.” Interestingly, while he accepts the fields present around a white dwarf will be unachievable in a laboratory in the foreseeable future, he sees an alternative way the group’s models might be tested experimentally. Rydberg atoms are highly excited atoms that can be the size of the dot of an “i”. Because the bond length between Rydberg atoms is so great, the Coulomb interaction is much smaller, and Schmelcher believes it might therefore be possible to use them to produce magnetic fields of comparable strength.
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Written by physicsgg

July 21, 2012 at 7:53 am

Posted in ATOMIC PHYSICS, Chemistry

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Dynamic Earth

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Watch as this NASA animation shows the sun blasting out a giant explosion of magnetic energy called a coronal mass ejection and the Earth being shielded from this by its powerful magnetic field. The sun also continuously showers the Earth with light and radiation energy. Much of this solar energy is deflected by the Earth’s atmosphere or reflected back into space by clouds, ice and snow. What gets through becomes the energy that drives the Earth system, powering a remarkable planetary engine — the climate.

The unevenness of this solar heating, the cycles of day and night, and our seasons are part of what cause wind currents to circulate around the word. These winds drive surface ocean currents and in this animation you can view these currents flowing off the coast of Florida.

This animation connects for the first time a series of computer models. The view of the sun and the Earth’s magnetic field comes from the Luhmann-Friesen magnetic field model and two models that incorporated data from a real coronal mass ejection from the sun on December 2006.

NASA’s Community Coordinated Modeling Center (CCMC) at Goddard Space Flight Center, a multi-agency partnership that provides information on space weather to the international research community, generated these two models. The ENLIL model is a time-dependent 3-D magnetohydrodynamic model of the heliosphere and shows changes in the particles flows and magnetic fields.
The BATS-R-US model is also a magnetohydrodynamic model of plasma from solar wind moving through the Earth’s magnetic dipole field. It uses measurements of solar wind density, velocity, temperature and magnetic field by NASA’s Advanced Composition Explorer (ACE) satellite, which launched in August of 1997 and the Solar Terrestrial Relations Observatory (STEREO), two satellites that view the structure and evolution of solar storms.

The view of the Earth’s atmosphere comes from the Modern-Era Retrospective Analysis for Research and Applications (MERRA), a computer model that uses data from the Goddard Earth Observing System Data Assimilation System Version 5 (GEOS-5) and incorporates information gathered from ground stations, operational satellites and NASA’s Earth-observing fleet of satellites. The model for the ocean is the Estimating the Circulation and Climate of the Ocean, Phase II (ECCO2), a joint project of the Massachusetts Institute of Technology in Cambridge, Mass. and NASA’s Jet Propulsion Laboratory in Pasadena, Ca.

Written by physicsgg

June 20, 2012 at 6:26 am


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Scientists Chart High-Precision Map of Milky Way’s Magnetic Fields

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The sky map of the Faraday effect caused by the magnetic fields of the Milky Way. Red and blue colors indicate regions of the sky where the magnetic field points toward and away from the observer, respectively. The band of the Milky Way (the plane of the Galactic disk) extends horizontally in this panoramic view. The center of the Milky Way lies in the middle of the image. The North celestial pole is at the top left and the South Pole is at the bottom right. (Image Credit: Max Planck Institute for Astrophysics)

Scientists at the Naval Research Laboratory are part of an international team that has pooled their radio observations into a database, producing the highest precision map to date of the magnetic field within our own Milky Way galaxy.
The team, led by the Max Planck Institute for Astrophysics (MPA), used the database they created and were able to apply information theory techniques to produce the map, explains NRL’s Dr. Tracy Clarke, a member of the research team. “The key to applying these new techniques is that this project brings together over 30 researchers with 26 different projects and more than 41,000 measurements across the sky. The resulting database is equivalent to peppering the entire sky with sources separated by an angular distance of two full moons.” This incredible volume of data results in a new, unique all-sky map that gives scientists the ability to measure the magnetic field structure of the Milky Way in unparalleled detail.

The map shows scientists a quantity known as Faraday depth, a concept that depends on magnetic fields along a specific line of sight. The research team created the map by combining the more than 41,000 individual measurements using a unique image reconstruction technique. The researchers at MPA are specialists in the new discipline of information field theory. Dr. Tracy Clarke, working in NRL’s Remote Sensing Division, is part of the team of international radio astronomers who provided the radio observations for the database. The new, high-precision map not only shows the Galactic magnetic field’s structure on large scales, it also reveals small-scale features that help scientists better understand turbulence in the Galactic gas…..
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Written by physicsgg

February 3, 2012 at 5:50 pm

World record: The strongest magnetic fields created

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On June 22, 2011, the Helmholtz-Zentrum Dresden-Rossendorf set a new world record for magnetic fields with 91.4 teslas. To reach this record, Sergei Zherlitsyn and his colleagues at the High Magnetic Field Laboratory Dresden (HLD) developed a coil weighing about 200 kilograms in which electric current create the giant magnetic field – for a period of a few milliseconds. The coil survived the experiment unscathed.

“With this record, we’re not really that interested in reaching top field values, but instead in using it for research in materials science,” explains Joachim Wosnitza, the HLD’s Director. The scientists are actually proud of being the first user lab worldwide to make such high magnetic fields available for research. The more powerful a magnetic field is, the more precisely the scientists can examine those substances which are used for innovative electronic components or for so-called superconductors which conduct electricity without any resistance. Such high magnetic fields are generated by passing an  through a copper coil….. Read the rest of this entry »

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June 28, 2011 at 8:11 pm


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Can humans sense the Earth’s magnetism?

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For migratory birds and sea turtles, the ability to sense the Earth’s magnetic field is crucial to navigating the long-distance voyages these animals undertake during migration. Humans, however, are widely assumed not to have an innate magnetic sense. Research published in Nature Communications this week by faculty at the University of Massachusetts Medical School shows that a protein expressed in the human retina can sense magnetic fields when implanted into Drosophila, reopening an area of sensory biology in humans for further exploration.

In many , the light-sensitive chemical reactions involving the flavoprotein cryptochrome (CRY) are thought to play an important role in the ability to sense the Earth’s magnetic field. In the case of , previous studies from the Reppert laboratory have shown that the cryptochrome protein found in these flies can function as a light-dependent .

To test whether the human cryptochrome 2 protein (hCRY2) has a similar magnetic sensory ability, Steven Reppert, MD, the Higgins Family Professor of Neuroscience and chair and professor of neurobiology, graduate student Lauren Foley, and Robert Gegear, PhD, a post doctoral fellow in the Reppert lab now an assistant professor of biology and biotechnology at Worcester Polytechnic Institute, created a transgenic Drosophila model lacking its native cryptochrome protein but expressing hCRY2 instead. Using a behavioral system Reppert’s group previously developed, they showed that these transgenic flies were able to sense and respond to an electric-coil-generated magnetic field and do so in a light-dependent manner.

These findings demonstrate that hCRY2 has the molecular capability to function in a magnetic sensing system and may pave the way for further investigation into human magnetoreception. “Additional research on magneto sensitivity in humans at the behavioral level, with particular emphasis on the influence of magnetic field on visual function, rather than non-visual navigation, would be informative,” wrote Reppert and his colleagues in the study.

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Written by physicsgg

June 22, 2011 at 7:48 am

Posted in BIOLOGY

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