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Artificial modification of the ionosphere by injecting high-power HF radio waves — a process often known as “heating” — produces a great number of phenomena. Of particular interest at Lancaster has been the optical emission, known as the "artificial aurora" which can be produced. To explain the intensity of the emission, it is necessary to understand how a sufficient number of electrons with energies high enough to stimulate the optical emission from atomic oxygen can be produced. If the electrons are simply the more energetic ones from a thermal (i.e. Maxwellian) velocity distribution then an apparently unrealistic electron temperature is required to account for the observations. This suggests that an acceleration mechanism which produces high-energy electrons with a non-thermal distribution may be responsible. It is thought that the source of the energetic electrons might be inside “striations” (field-aligned irregularities in the electron density which are enhanced during heating). Modelling of the electron temperature distribution within these striations has been carried out to compare with observations made by incoherent scatter using the EISCAT radar.

Figure: Electron temperature enhancements during heating as observed by EISCAT.

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