Magnetosphere particle motion

As discussed further below, that extent depends very much on the direction of the Interplanetary Magnetic Field, in particular on its southward or northward slant.

Furthermore, Birkeland currents and heat flow are also channeled by such lines — easy along them, blocked in perpendicular directions.

Indeed, field lines in the magnetosphere have been likened to the grain in a log of wood[citation needed], which defines an "easy" direction along which it easily gives way.

Thus magnetic fields (like the Earth's) can profoundly affect particle motion in them, but need no energy input to maintain their effect.

[citation needed] However, as noted before, the total energy of a particle in a "purely magnetic" field remains constant.

Magnetic mirroring makes possible the "trapping" in the dipole-like field lines near Earth of particles in the radiation belt and in the ring current.

On all such lines the field is much stronger at their ends near Earth, compared to its strength when it crosses the equatorial plane.

Only particles whose motion is very close to parallel to the field line, with near-zero μ, avoid mirroring—and these are quickly absorbed by the atmosphere and lost.

[citation needed] In addition to gyrating around their guiding field lines and bouncing back and forth between mirror points, trapped particles also drift slowly around Earth, switching guiding field lines but staying at approximately the same distance (another adiabatic invariant is involved, "the second invariant").

The gyration around the guiding field line is therefore not a perfect circle, but curves a little more tightly on the side closer to the Earth, where the larger B gives a smaller Rg.

[citation needed] In the 1980s, a "plasma fountain" of hydrogen, helium, and oxygen ions was discovered flowing from the Earth's North Pole.

A sketch of Earth's magnetic field representing the source of Earth's magnetic field as a magnet The North Pole of Earth is near the top of the diagram, the South Pole near the bottom. Notice that the South Pole of that magnet is deep in Earth's interior below Earth's North Magnetic Pole . Earth's magnetic field is produced in the outer liquid part of its core due to a dynamo that produce electrical currents there.
A simulation of a charged particle being deflected from the Earth by the magnetosphere.
Schematic view of the different current systems which shape the Earth's magnetosphere
A simulated charged particle, its trajectory determined primarily by the Earth's magnetosphere.
The Earth's " plasma fountain ", showing oxygen, helium, and hydrogen ions which gush into space from regions near the Earth's poles. The faint yellow area shown above the north pole represents gas lost from Earth into space; the green area is the aurora borealis -or plasma energy pouring back into the atmosphere. [ 2 ]