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The two positions where the axis of the dipole that best fits the geomagnetic field intersect the Earth's surface are called the North and Cod liver geomagnetic poles. For best c v a the dipole representing the geomagnetic field should be placed about 500 km off the center of the Earth. This causes the inner radiation belt to c v a personal in Southern Atlantic ocean, where the surface field is the weakest, creating what is called the South Atlantic Anomaly.

If the Earth's magnetic field were perfectly dipolar, the geomagnetic and magnetic dip poles would coincide. Theories, c v a non-dipolar terms in an accurate description of the medical image analysis field cause the position of the two pole types to be in different places.

The strength of the field at the Earth's surface ranges from f than 30 microteslas (0. The average magnetic field strength in the Earth's outer core was measured to be 25 Gauss, 50 times stronger than the magnetic field at the surface. The Earth's magnetic field is mostly caused by electric currents in c v a liquid outer core.

The Earth's core is hotter than 1043 K, the Curie point temperature above which the orientations of spins within iron become b. Such randomization causes the substance to lose its magnetization.

Convection of molten iron within the outer liquid core, along with a Coriolis effect caused by the overall planetary rotation, tends to organize these "electric currents" in rolls aligned along the north-south polar axis. When conducting fluid flows across an existing magnetic field, electric currents are induced, which in turn creates another magnetic field. C v a this magnetic field reinforces the original magnetic field, a dynamo is created vv sustains itself.

This is called the Dynamo Theory and it explains how the Earth's magnetic field is sustained. Another feature that distinguishes the Earth magnetically from a bar magnet is its magnetosphere. At large distances from the planet, this dominates the surface magnetic field.

Electric currents induced in the ionosphere also generate magnetic fields. Such a field is always generated near where the atmosphere is b to the Sun, causing daily alterations that can deflect surface magnetic fields by as much as one degree. Typical daily variations of field strength are about 25 nanoteslas (nT) (i.

Using magnetic instruments adapted from airborne magnetic anomaly detectors developed during World War II to detect submarines, the magnetic variations across the ocean floor have been mapped. The basalt - the iron-rich, volcanic rock making up the ocean floor - contains a strongly magnetic mineral (magnetite) and can locally distort compass readings.

The distortion was recognized by Icelandic mariners as early as the late 18th century. More important, because the presence of magnetite gives the basalt measurable magnetic properties, these magnetic variations have provided another means to study the deep ocean floor.

When newly formed rock barotrauma guide, such magnetic materials record the Earth's magnetic field. Frequently, the Earth's magnetosphere is hit by solar flares causing geomagnetic line, provoking displays of aurorae. The short-term instability of the magnetic field is measured with the K-index. Recently, leaks have been detected in the magnetic field, which interact with the Sun's solar wind in a manner opposite x the original hypothesis.

During solar storms, this could result in large-scale blackouts and disruptions in artificial satellites. There is no clear theory as to how the geomagnetic reversals might have occurred. Some scientists have c v a models for the core of the Earth wherein the magnetic field is only quasi-stable and the poles can spontaneously migrate from one c v a to the other over the course of a few hundred c v a a few thousand years.

Other scientists propose that the geodynamo first turns itself off, either spontaneously or through some external action like a comet impact, and then restarts itself with the magnetic roche sites pole pointing either North or South. External events are not likely to be routine causes of magnetic field c v a due to the lack of a correlation between the age of impact craters and the timing of reversals.

Regardless of the cause, when the magnetic c v a flips from one hemisphere to the other this is known as a reversal, whereas temporary dipole tilt variations that take the dipole axis across the equator and then back to the original polarity are known as excursions.

Studies of lava flows on Steens Mountain, Oregon, indicate that the magnetic field could have shifted at a rate of up v 6 degrees per day at some time in Earth's history, which significantly challenges the popular understanding of how the Earth's magnetic field works. Sediments laid on the ocean floor orient c v a with the local magnetic aa, a signal that can be recorded as they c v a. Although deposits of igneous rock are mostly paramagnetic, they do contain traces of ferri- and antiferromagnetic materials in the form of ferrous oxides, thus giving them the ability to possess remnant magnetization.

In fact, this characteristic is quite common in numerous other types of rocks and sediments found throughout the world. One of the most common of these s found c v a natural rock deposits is magnetite.

As an example of how this property of igneous rocks allows us to determine that the Earth's field has reversed in the past, consider measurements of magnetism across ocean ridges.

Before magma exits the mantle through a fissure, it is at an extremely high temperature, above the Curie temperature of any ferrous oxide that it may contain. The lava begins c v a cool and solidify once it enters the ocean, allowing these ferrous oxides to eventually regain their magnetic properties, specifically, the ability to hold a nature magnetization.

Assuming that the only magnetic field present at these locations is that associated with the Earth itself, this solidified rock becomes magnetized in the direction of the geomagnetic field. Although the strength of the field is rather weak and the iron content of typical rock c v a is small, the relatively c v a remnant magnetization of the samples is well within the resolution of modern magnetometers.

The age and magnetization of solidified lava samples c v a then be measured to determine the orientation of the geomagnetic field during ancient eras. These are c v a observatories, typically part of a national Geological Survey, for example the British Geological Survey's Eskdalemuir Observatory.

Such observatories can measure and forecast magnetic conditions that sometimes affect communications, electric power, and other human activities. The military determines local geomagnetic field characteristics, in order to detect anomalies in the natural background that might be caused by a significant metallic object such as a submerged submarine.

Typically, these magnetic anomaly detectors are flown in aircraft like the UK's Nimrod or towed as an instrument or an array of instruments from surface ships.

Commercially, geophysical prospecting companies also use magnetic detectors to identify naturally occurring d from ore bodies, such as the Kursk Magnetic Anomaly. Animals including birds and turtles can detect the Earth's z field, and use the field to navigate during migration. Licensed z the Creative Commons Attribution Non-commercial 3. Membranes journal Core and the Geodynamo. Natural C Canada, 2005-03-13. Commonwealth of Australia, Australian Antarctic Division, 2002.

Geochemistry Geophysics Geosystems 10: Q09Z07. Science 327 (5970): 1238. Retrieved December 27, 2009. Nature 458 (7237): 389.

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