Magnetosphere

Earth, like planets, Sun and even galaxies is surrounded by a large magnetic field. For Earth, this is the so-called magnetosphere. Magnetosphere is a vast comet-tail shaped area beginning at Earth Sun side and extending beyond Earth. It is the space manifestation of Earth's magnetic field, the one which acts upon compass' needle. Earth's magnetic field is a gigantic dipole magnet axis of which is slightly different from Earth's axis; this difference yields magnetic poles being located at different places than geographical ones. Earth magnetic lines extend into surrounding space

It is the solar wind which is shaping Earth's magnetosphere: sunwards the solar wind compresses Earth's magnetic field; on the opposite side it shapes it comet-tail. Solar wind is a ions plasma emanating from Sun and carrying with it the latter's magnetic field. Sunwards, solar wind hits magnetosphere at the bow shock. It is the place where Earth's magnetic field abruptly deflects solar particles and magnetic field. This compressed part of the magnetosphere extends to about 6-10 Earth radii from Earth. The encounter between the solar wind and Earth's magnetic field is generating sonic booms! Two polar cusps along magnetosphere axis allow solar wind to reach upper part of the atmosphere. Magnetosphere's comet-tail side extends up to 1,000 Earth radii. Some solar particles which somehow managed to reach there form the "plasma sheet". The so-called neutral sheet stays at the middle of it. It is where northern and southern part of the Earth's magnetic field cancel. Plasma sheet is too a coating of sort for magnetosphere's tail. Each side of plasma sheet are found tail lobes. Boundary between magnetosphere and interplanetary medium is called the magnetopause

Related to Earth protective shield are too an Earth atmosphere's part and the famous Van Allen belts. Ionosphere is Earth's atmospheric layer populated by charged particles. A part of these particles leaks into the plasmasphere which is a spherical zone more directly part of magnetosphere. In plasmasphere are found Van Allen belts. Van Allen belts are tori of charged particles: inner belt is made of high-energy protons resulting from upper atmosphere being knocked by cosmic rays as outer belt is high-energy electrons yielded by cosmic rays and magnetosphere acceleration

Strong Events Inside the Van Allen Belts
A fortuitous bounce of activity inside the Van Allen belts during that the new solar satellites STEREO entered there has shown that radio-frequency waves called 'whistlers' in the belts, which are accelerating the electrons found there, up to 99 percent of the speed of light, are doing that in just a tenth of a second, and not spans of minutes or tens of hours like previously thought

Magnetosphere is a dynamic medium in connection with solar wind especially with solar eruptions. These may lead to magnetosphere's outer part being punctured magnetotail side, solar wind and magnetic lines enter there and break Earth magnetic lines. Ensuing mixed solar-Earth magnetic lines flow into tail, compressing plasmasheet from both sides. Earth parts of magnetic lines eventually reconnect. Earthside lines violently snap back Earth (this is a so-called "reconnection" process); they carry solar wind particles with them; these funnel into polar cusps down to upper atmosphere and yield the famous auroras or Northern Lights through an 'auroral oval'. Sudden, powerful brightening, and increased dynamism of Northern Lights are called 'substorms', as their mechanism is still ill-known. In any case, they originate into the magnetosphere's tail, from where an increase in the solar particles snaps back into the northern regions of Earth. On magnetosphere's tail side a solar plasma bubble is expelled from magnetosphere. Solar events and auroras may work too directly from magnetosphere Sun's side: solar and terrestrial lines connect yielding so-called "cracks" which are punctures in Earth magnetic shield. Solar wind enters puncture and follows magnetic lines to polar cusps there too yielding Northern Lights. Recent findings showed that cracks may last up to 9 hours
On the other hand, major solar events in fall 2003 showed how powerful solar streams may further affect the Earth environment as the plasmasphere was blown out, through the poles, to the magnetopause, as a new radiation belt formed at its place. It lasted more than five weeks before being drained away or absorbed by Earth's atmosphere

Ion Plumes in the Ionosphere, a By-Product of Geo-Magnetic Storms
The ionosphere, when a coronal mass ejection (CME) strikes the Earth's magnetic field, is the place where 'ion plumes' may linger, scientists recently discovered, with effects on GPS, transmissions, airline navigation and radio communications. Such plumes are ionized air (air with an excess electron density) at high altitudes, moving at speed of 2200 mph -1 km/s- (1400 km/h, 1 km/s), as they might originate at the point where the effect of the CME hit is felt near the magnetic equator, over Africa that is. As such plumes form in the ionosphere, they may leak back too into space

As far as the origins of the Earth's magnetic field are concerned, they are thought to be due to the interaction between the two varieties of Earth's core: a liquid core exists around a solid inner core and both acts like a dynamo. Earth's magnetic field is a living system. Its axis e.g. is varying and as a result magnetic poles are drifting: north magnetic pole is drifting from Canada to Siberia. Another major change the magnetic field endures is reversals: it flips, north pole becoming south and vice versa. These reversals occur about each 300,000 years. Last occurred 780,000 years ago. Reversals do not occur suddenly but they take a few thousand years to complete. During this evolving phase, the magnetic field does not show its dipole bar magnet classical aspect anymore: its it tangled and complicated instead, magnetic poles may be located anywhere on Earth's surface, and there may be more of them than the usual two. Reversals modify magnetosphere but do not make it disappear however and it still protects Earth. Earth's magnetic field has been monitored to have weakened by 10 per cent since the 19th century. This decline has to be put in perspective however as the field today is about twice as strong as normal. It is thought too that this decline would better be the sign that the magnetic field is at the onset of a so-called "excursion" which sees the field swiftly reverse and back over a period of about 400 years

Themis sees More About the Geomagnetic Substorms and Auroras
The Themis mission, which is dedicated to study auroras, has recently shown that geomagnetic substorms and auroras might well be triggered by 'magnetic ropes' directly connecting the Sun to the upper part of the Earth's magnetosphere, the 'magnetopause', at about 40,000 miles (64,000 km) above Earth. Such direct links seem to occur all time, forming and unraveling in a just some minutes, providing however enough time thus, to a brief but significant conduit between the Sun and the Earth. Another solar trick is that the solar wind sometimes affected with knots of magnetism. When such knots reaches the bow shock of the magnetosphere, an explosion occurs, which boosts the temperature of the solar wind particles by ten-fold up to as high as 10 million degrees. Such so-called 'hot flow anomalies' (HFAs) don't play however a significant role into the geomagnetic storms as they are too infrequent

The Plasmasphere, the Major Contributor to the Magnetosphere During Superstorms!
Recent studies in 2008 showed that the protons in the plasmasphere have the most efficient effect unto the magnetosphere state during solar superstorms, with it squashed and pressurized by the solar wind and forming a long tail called the plasmaspheric plume where the protons are further energized by the solar wind. When the particles re-enter the magnetosphere, they are the main contributors to it then