The Optical Aurora

The aim of this book is to describe and discuss the aurora as an optical phenomenon, one which can be observed by the naked eye as well as with more sensitive optical detectors. It continues the tradition of study ing that impressive and imaginative play of nature, the northern lights, seen and discussed by the Greek philosphers as early as the sixth century B.c. Today the study of the optical aurora is only one of many ways of acquiring information about a major phenomenon: the ejection of plasma from the sun, the interaction of this plasma with the geomagnetic field and the injection of fast particles into the earth's atmosphere. of the optical aurora is justified by the Hence, the separate treatment particular scientific approach: detection and interpretation of electro magnetic radiation, approximately in the 1000-100000 A region, produc ed through interaction between the auroral particles and the earth's atmosphere. Other techniques, such as radio observations, X-ray observations, direct particle detections from rockets and satellites, studies of magnetic storms, and measurements of the magnetic field and plasma properties in the magnetosphere, are as important or more important than the classical way of studying the optical aurora. Nevertheless, it was felt worthwhile to treat the optical aurora in a separate book, perhaps mainly because today one author cannot master the whole subject with sufficient competence. This book is thus one volume in a series of books giving a more complete picture of physics and chemistry in space.

Inhalt
1 The Occurrence and Cause of Auroras: a Short Introduction.- 1.1 Local Auroral Forms.- 1.2 Auroral Morphology.- 1.3 Particle Behaviour: Reflection, Absorption and Scattering.- References.- 2 The Electron Aurora: Main Characteristics and Luminosity.- 2.1 Introduction.- 2.2 N2+ Emission and Ionization.- 2.3 Theoretical Height Distribution of the First Negative N2+ Bands.- 2.4 Height Distribution of Other Emissions.- 2.5 Electron Energies Inferred from Height Distribution of Auroral Luminosity.- 2.6 Geometry and Motion of the Electron Aurora.- 2.7 Latitude Variations in Auroral Heights.- References.- 3 The Proton Aurora.- 3.1 Introduction.- 3.2 Theory of Hydrogen Line Emission.- 3.3 Observations on Hydrogen Lines.- References.- 4 The Optical Spectrum of Aurora.- 4.1 Description.- 4.2 Local Variations in the Spectrum.- 4.3 Latitudinal and Zonal Variations.- References.- 5 Physics of the Optical Emissions.- 5.1 Excitation.- 5.2 Deactivation.- 5.3 Interpretation of the Spectrum.- 5.4 The Lifetime of Metastable Oxygen Atoms.- 5.5 Helium Emissions.- 5.6 Sunlit Aurora.- Appendix (References to Data on Cross-Sections).- References.- 6 Temperature Determinations from Auroral Emissions.- 6.1 Introduction.- 6.2 Doppler Temperatures.- 6.3 Rotational Temperatures.- 6.4 Conclusions and Prospects.- References.- 7 Pulsing Aurora.- 7.1 Introduction.- 7.2 Pulsating Aurora.- 7.3 Flaming Aurora.- 7.4 Flickering Aurora.- 7.5 Streaming Aurora and Horizontal Waves.- 7.6 Correlation with Pulsations in the Magnetic Field and Telluric Currents.- 7.7 Correlation with Pulsations in X-Rays.- 7.8 Morphology of Pulsating Aurora.- References.- 8 Optical Aurora and Radio Observations.- 8.1 Introduction.- 8.2 Radio Absorption.- 8.3 E-Layer Ionization.- 8.4 Radio Auroras.- 8.5 VLF Radio Emissions and Radio Noise.- 8.6 Polar Cap Absorption (PCA) Events.- References.- 9 Auroral X-Rays.- 9.1 Production of X-Rays in Aurora.- 9.2 Observations.- References.