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A population of protons with energy of some tens of keV, called the ring current, is found near the equatorial region of the magnetosphere at several earth radii. During the main phase of geomagnetic storms the ring current shifts toward lower L values into the region of the plasmapause, which is characterized by steep gradients in the plasma density. This interaction together with an anisotropic pitch angle distribution leads to ring current instability and the growth of ion cyclotron wave turbulence. As wave energy is dissipated in the ambient electron gas by Landau damping, the plasmapause electron temperature is raised to a few electron volts, and a substantial temperature gradient is created with respect to the ionosphere. The energy transferred to the ionosphere by pitch angle scattering in the low collision frequency region and by heat conduction in the collision‐dominated regime raises the ionospheric electron temperature to several thousand degrees. Therefore an appreciable number of electrons in the high‐energy tail of the Maxwellian distribution, i.e., electrons with energy greater than 2 eV, exist in the F region of the ionosphere at about 400 km, where atomic oxygen is the dominant neutral gas constituent. Two eV is the threshold for excitation of oxygen atoms to the metastable ¹D level, and these O(¹D) atoms emit 6300‐Å radiation, the signature of stable auroral red (SAR) arcs. Although the energy input rate required to produce electron temperatures sufficient to cause average SAR arcs is less than 0.1 erg cm−2 s−1, the energy radiated in the red line is only about 0.003 erg cm−2 s−1. Thus an SAR arc is an optical manifestation of a slow release of energy from the magnetosphere during a geomagnetic storm. Energetically it is small in comparison with high‐latitude auroral processes.

This textbook focuses on the physics and chemistry of the Earth's upper atmosphere, which is bounded at the bottom by a pressure level at which most of the incoming ionizing radiation has been absorbed, and bounded at the top by the level at which the escape of gas becomes important. The plan of the book is to identify the multitude of processes that operate in the upper atmosphere, and to relate them to observed phenomena by detailed mathematical and physical descriptions of the governing processes. Basic information from many disciplines such as radiation physics and chemistry, fluid dynamics, optics, and spectroscopy is skilfully marshalled to give a coherent account of the upper atmosphere. This book is outstanding as an introduction to the primary literature and current problems for students of physics or chemistry. The text is supported by numerous diagrams, bibliography and index.

The relationship between auroral electron fluxes and spectroscopic emission features in aurora is quantitatively explored. The model computations focus on the prominent auroral radiations of atomic oxygen at 6300 Å and 5577 Å and a vibrational band of ionized molecular nitrogen at 4278 Å. The emission rate ratios, 6300/4278, 5577/4278, and 6300/5577, together with the absolute emission rate of the 4278‐Å radiation, may be used to infer a characteristic energy of the precipitating electron flux. This characteristic energy and the 4278‐Å intensity then determine the total electron flux and the energy deposition rate. Computational results are presented in easily used curves, and the assumptions made in the model calculations are discussed in the text. At the present time it appears that the ratio 6300/4278 is the most reliable and informative of the set.

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