The Magnetopause
The Magnetopause

The outer boundary of the magnetosphere is called the magnetopause. It is the valve which controls what gets in and out. As the shocked solar wind in the magnetosheath rushes past the magnetopause boundary it causes the plasma in the outer magnetosphere to try to move along with it, by either wave viscosity or magnetic reconnection. Wave viscocity is similar to the way a wind blowing over water generates waves that cause the water to move. Magnetic reconnection is how the interplanetary and Earth's magnetic fields can connect across the magnetopause boundary. The reconnected magnetic field lines communicate the motion of the plasma hundreds of thousands of kilometres away in the shocked solar wind into and through the magnetosphere to just a hundred kilometres above the Earth's surface, pulling along the plasma there. This is like how a kite line communicates the motion of a kite in the wind down to the ground, pulling along the kite flyer if she or he is not strong enough! Not only does plasma move along with the magnetic field lines but its ionised particles also move freely up and down them. In this way, the reconnected magnetic field also allows solar wind particles to enter the magnetosphere more directly, mainly through the cusp region.

AMPTE ATS-6 Interball
Polar GOES ISEE 1 and 2

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