Charged Particle Motion in Earth's Magnetosphere

Particle Sources and Energy Levels

Auroral displays are caused by energetic particles flowing along magnetic field lines from deep in the magnetotail to the upper atmosphere. Most of these particles are electrons, but protons and other ions may also be present.

Animations courtesy the COMET and HAO programs at UCAR/NCAR.

Auroral particles are one of the many categories of energetic particles that bombard the Earth. These include extremely high-energy fluxes of particles in the GeV or MeV range, such as cosmic rays, high-energy radiation belt particles, and solar energetic particles. Auroral particles originating in the magnetospheric plasma sheet are generally in the 1 to10 keV energy range, but can sometimes be as high as 100 keV. Less energetic particles (in the 100s of electron-volts) such as solar wind entering the magnetosphere in the dayside cusp regions near the magnetic poles, also impact the upper atmosphere.

Categories of energetic particles.

  Cosmic Rays Solar Energetic Particles Radiation Belt Particles Auroral Particles Solar Wind Particles
mostly protons
electrons and protons
electrons and protons
electrons and protons
interstellar space
the Sun
Energy Ranges (eV)
109 - 1018+
107 - 109
106 - 107
103 - 105

Various types of particle radiation from space penetrate to different levels in Earth's atmosphereThe depth to which particles penetrate the atmosphere depends on their energy; the more energetic they are, the deeper they travel. Cosmic rays can reach the troposphere or even the surface of the Earth; solar energetic particles and radiation belt particles can reach the stratosphere and mesosphere; and auroral particles reach the lower thermosphere, usually around 100 kilometers. Auroral particles entering the atmosphere are far more numerous than the others, which is why auroral displays are seen.

Last modified August 29, 2005 by Randy Russell.

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