MAGNETOSPHERE: WHAT ISIT?
The magnetosphere is the region of theterrestrial environment where the geomagnetic field exerts the dominatinginfluence. In the absence of an interplanetary plasma, the Earth's dipole fieldwould extend infinitely in all directions. However, the geomagnetic fieldproduces an obstacle to the solar wind and the resulting interaction produces acavity around which most of the plasma flows. In space, the region above theionosphere is called the magnetoshere.
SHAPE OF THEMAGNETOSPHERE
The extent of the magnetosphere isrelated to changes in the solar wind density and velocity, and to variations inthe strength and orientation of the IMF. The surface where the compressedgeomagnetic field force balances the force of the solar wind plasma is calledthe magnetopause. As the solar wind is blasted on the Earth, it compresses thesunward side of the magnetosphere, and drags it out on the night side into atail called the magnetotail upto 1000 Earth radii. The bulk of the solar wind plasma is diverted around themagnetosphere and does not approach the earth any closer than the magnetopause.The magnetopause occurs approximately 10 Earth radii (10Re) on the sunward sideand magnetotail extends well beyond the Moon's orbit (60 Re) on the oppositeside. The magnetosphere assumes the shape of a bullet, blunt on the sunward sideand extended like a cylinder for a long distance in the anti-sunward direction.
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| The solar wind travels at supersonic speeds ininterplanetary space. When it reaches the magnetosphere, a bow shock or a shockwave (nose at about 15 Re) develops in front of the magnetopause. The regionbetween the magnetopause and the bow shock is called the magnetosheathconsisting of disordered field, mixed with irregularly distributed plasma.
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| Note that the shape of the magnetopause can be determined by requiring that the magnetic pressure just inside of the magnetopause balances the magnetosheath plasma pressure made up of both gas and dynamic pressures. When the dynamic pressure of the solar wind increases, the magnetopause moves closer to the Earth until the geomagnetic field is sufficiently intense to withstand the increased force of the solar wind. Likewise, a decrease in solar wind pressure leads to an expansion of the magnetosphere. |
The ionized gases in the magnetosphere take partin gigantic magnetospheric circulation called convection where the plasma overthe polar regions is swept away from the sun while the plasma outside theauroral zone (i.e. at lower altitudes) is swept toward the sun. At latitudesbelow about 60o, and at lower altitudes, no such convection is seen. Here theplasma corotates with the Earth.
The geomagnetic field at times can be disturbedby the occurrence of magnetic storm. The magnetic storm can involve a largenumber of substorms which can cause a small reduction in the geomagnetic fieldstrength over most of the Earth's surface due to an enhancement of the ringcurrent by the injection of energetic tail plasma. The most visible and wellknown products of substorms are the bright, active and extensive auroras.
If you need moreinformation about the magnetosphere, check out these cool links
 | http://ssdoo.gsfc.nasa.gov/education/lectures/magnetosphere.html#intro |
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