Particle Motion in the Magnetosphere

Particle Motion in the Magnetosphere


Electrons and ions gyrate about a field line in oposite directions. The period of gyration depends on the magnetic field strength and the mass of the particle. The stronger the magnetic field is, the smaller the gyro-period is; and the heavier the particle is, the bigger the gyro-period is. For magnetic field strengths typical of the inner magnetosphere, the electron gyro-period is of the order of 1.E-4 - 1.E-3 seconds while the heavier protons have gyro-periods of the order of 0.1 - 1 seconds.

Electron and Proton Gyro Periods [plot]


The bounce motion back and forth along a field line between the mirror points depends on the kinetic energy of the particles. The faster a particle is the smaller the bounce period is. Electorns of 1 KeV in energy at L=10 have bounce period of ~ 1 second which is ~40 times smaller than the bounce period of a proton with the same energy.

Electron Bounce Period [plot] Proton Bounce Period [plot]


Partricles perform a slow longitudinal drift around the Earth. Electrons drift eastward while ions drift westward. The drift period depends on the enrgy of the particle and their pitch angle. A 10 keV particle with a 45 degree pitch angle will need ~12 hours to drift around the Earth.

Particle Drift Period [plot]