Wave acceleration of electrons in the Van Allen radiation belts

The Van Allen radiation belts are regions of space encircling the Earth where energetic particles from the solar wind are trapped by Earth's magnetic field. The high energies of these particles — millions of electron volts — make the belts a hazard to spacecraft. A better understanding of the mechanisms that accelerate particles to such high energies will make it easier to predict periods of enhanced risk for satellites, and a recent rare event provided an opportunity to test current models. The ‘Halloween’ solar storms of 2003 disrupted GPS and communications satellites, short-wave radio signals and power grids and caused red auroras as far south as Florida. In space, the outer of the two radiation belts was depleted, then reformed closer to Earth. Electromagnetic waves were seen to be the dominant process involved in accelerating electrons back up to speed, not the radial diffusion that had previously been suspected.