Charged particles within the Earth's radiation belts travel in spiral trajectories along geomagnetic field lines.
The strength of the magnetic field increases as the particles approach the Earth; because charge flows perpendicular to magnetic field lines, the component of the particles' velocity parallel to the magnetic field decreases.
Usually, this causes particles to reverse direction and spiral back along the field lines, continuing until they reach the opposite hemisphere, where they reverse again. These trapped particles can be deflected by certain electromagnetic waves (whistlers) into the Earth's dense atmosphere (below 100 kilometers (60 miles)), where they cannot escape back to the magnetosphere.
Noting that whistlers can be generated by ground-based transmission signals in the very low frequency range (VLF, used for military communications), Sauvaud et al. use satellite observations to investigate how a VLF transmitter located in Australia (labeled NWC) affects the population of inner radiation belt electrons first above it and then along the electron drift path around the Earth.
They find that about 300 times more high-energy electrons are lost by the inner radiation belt to the atmosphere during NWC transmission periods than during nontransmission periods, suggesting that human systems can control radiation belt dynamics.
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