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The Eart3

# The Eart3 - (gamma Thus where R M and B M are the...

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The Earth's Magnetosphere This gives an equation from which we can find the magnetic field strength at the boundary: From the magnetic field strength at the boundary we can calculate how far out the stand-off point will be from the earth, since we know that a dipole field falls off as distance-cubed (B prop. to 1/R 3 ). There is one complication, that the Earth's field is compressed by the solar wind flow and so we do not get a dipole fall-off as 1/R 3 , but rather a faster fall off of B from the earth, followed by a sudden drop to the value in interplanetary space (the IMF) at the magnetopause: The field magnitude at the boundary is actually twice what it would be without the compression, and so we are at a position where the dipole field would, without compression, be 27 nT

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Unformatted text preview: (gamma). Thus: where R M and B M are the distance (radial) to, and magnetic field at, the Magnetopause, and R e and B E the distance to and magnetic field at, the earth's surface at the same latituh's surface at the same latitude. For an equatorial position (i.e. [psi]=0), B E is the equatorial field strength. Putting in the relevant values gives a stand-off distance on this simple calculation of about 11R E . In general we have: A further complication is that the flow of solar wind is supersonic, and so there is a shock wave produced (the "bow shock") in front of the magnetopause, and a region of shocked flow between them:...
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The Eart3 - (gamma Thus where R M and B M are the...

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