Earth's magnetic field | Wikipedia audio article
Channel: wikipedia tts
Date: 2019-03-17

This is an audio version of the Wikipedia Article:
https://en.wikipedia.org/wiki/Earth%27s_magnetic_field


00:01:55 1 Significance
00:03:29 2 Characteristics
00:03:39 2.1 Description
00:04:20 2.1.1 Intensity
00:04:35 2.1.2 Inclination
00:05:18 2.1.3 Declination
00:05:59 2.2 Geographical variation
00:06:36 2.3 Dipolar approximation
00:06:52 2.4 Magnetic poles
00:07:43 3 Magnetosphere
00:09:40 4 Time dependence
00:12:49 4.1 Short-term variations
00:12:58 4.2 Secular variation
00:13:58 4.3 Magnetic field reversals
00:15:24 4.4 Earliest appearance
00:18:21 4.5 Future
00:18:42 5 Physical origin
00:20:11 5.1 Earth's core and the geodynamo
00:20:20 5.2 Numerical models
00:25:15 5.3 Currents in the ionosphere and magnetosphere
00:26:20 6 Measurement and analysis
00:26:58 6.1 Detection
00:27:07 6.2 Crustal magnetic anomalies
00:28:49 6.3 Statistical models
00:29:50 6.3.1 Spherical harmonics
00:30:12 6.3.2 Radial dependence
00:32:10 6.3.3 Global models
00:33:40 7 Biomagnetism
00:35:40 8 See also
00:36:39 9 References



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SUMMARY
=======
Earth's magnetic field, also known as the geomagnetic field, is the magnetic field that extends from the Earth's interior out into space, where it interacts with the solar wind, a stream of charged particles emanating from the Sun. The magnetic field is generated by electric currents due to the motion of convection currents of molten iron in the Earth's outer core: these convection currents are caused by heat escaping from the core, a natural process called a geodynamo. The magnitude of the Earth's magnetic field  at its surface ranges from 25 to 65 microteslas (0.25 to 0.65 gauss). As an approximation, it is represented by a field of a magnetic dipole currently tilted at an angle of about 11 degrees with respect to Earth's rotational axis, as if there were a bar magnet placed at that angle at the center of the Earth. The North geomagnetic pole, currently located near Greenland in the northern hemisphere, is actually the south pole of the Earth's magnetic field, and conversely.
While the North and South magnetic poles are usually located near the geographic poles, they slowly and continuously move over geological time scales, but sufficiently slowly for ordinary compasses to remain useful for navigation. However, at irregular intervals averaging several hundred thousand years, the Earth's field reverses and the North and South Magnetic Poles respectively, abruptly switch places. These reversals of the geomagnetic poles leave a record in rocks that are of value to paleomagnetists in calculating geomagnetic fields in the past. Such information in turn is helpful in studying the motions of continents and ocean floors in the process of plate tectonics.
The magnetosphere is the region above the ionosphere that is defined by the extent of the Earth's magnetic field in space. It extends several tens of thousands of kilometers into space, protecting the Earth from the charged particles of the solar wind and cosmic rays that would otherwise strip away the upper atmosphere, including the ozone layer that protects the Earth from harmful ultraviolet radiation.