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Keywords:

  • chorus;
  • distribution;
  • plasmapsheric hiss;
  • radiation belts;
  • ray tracing;
  • wave normal

Arcing from pole to pole, the Van Allen radiation belts are formed from a large number of protons or electrons trapped high above the Earth, the high-energy particles locked in paths dictated by the terrestrial magnetic field. Separating the outer electron Van Allen belt from the inner belt is the so-called slot region, a safe zone with reduced radiation levels. Not a necessary feature of the radiation belts, the safe zone is formed when low-frequency radio waves known as plasmaspheric hiss kick the high-energy electrons out of their trapped orbits. Understanding the safe zone depends on sorting out the hiss waves' basic properties, including their spatial and frequency distributions, and their typical direction of propagation—not an easy task, as indicated by decades of conflicting observations.