Atmospheric excitation and ionization by ions in strong auroral and man-made electric fields

Ions gyrating in crossed electric (E) and magnetic (B) fields may acquire an energy of 2mE2B2. In electric fields found near auroras, ions acquire sufficient energy to excite and sometimes also to ionize molecules. On the assumption that the subsequent emission contributes significantly to the glow outside of discrete auroral forms, cross-sections for excitation of atmospheric species by low energy ions (1–30 eV) are found. When these cross-sections become known, the electric field may be estimated from ground-based measurements of this glow. At the greater field strengths (≳ 250 mV/m) ionization of the air and also excitation of helium to the 23S state may occur. The ionization may be sufficient to sustain the ionosphere near the aurora. An experiment to test the theory is proposed in which Ba+ (a heavy ion) is injected into the auroral ionosphere. The need for cross-sections for excitation and ionization by ions is evident to understand the physics of strong electric fields in the ionosphere and vice versa, field and photometric measurements in the auroral atmosphere may provide useful guide-lines in designing laboratory experiments. The application of strong (by natural standards) electric fields to the upper atmosphere from rockets or orbiting vehicles and study of the resultant glows should be of value in understanding not only aspects of the aurora but also of the electrodynamics of the thermosphere.