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  • Communications Effects of Space Weather
  • VLF, LF, MF propagation

VLF, LF, MF propagation

  • Propagation of these frequencies is controlled by the lower regions of the ionosphere - mostly the D and the E layers although sometimes the F layer at night). Propagation is therefore subject to variations of the ionosphere some determined by the sun and space weather. Solar flares and their effects on the D region is one such influence. The intense flux of X-rays during a major flare increases the ionisation of the D region changing its ability to reflect in these bands. For the lowest frequencies - VLF - propagation of the signal occurs as the conducting earth and the ionosphere act as a waveguide. Flares usually have a very rapid onset - measured in minutes - and this results in sharp changes in the amplitude and phase of signals as the waveguide height changes.

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