... Geomagnetic field lines can guide energetic electrons and protons from magnetosphere or magnetosheath down to Earth's atmosphere . Precipitating particles loose their energy via collisions with the neutral particles and ionize them at approximately the same altitude range than solar UV radiation when creating the ionosphere . In addition, some of the atmospheric constituents are excited to higher energy levels: this can lead to emission of auroral light. ... ISPEC page on aurora . ...