The Optical Aurora

ISBN-13: 9783642462719 / Angielski / Miękka / 2012 / 200 str.

A. Omholt

Opis

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."

Spis treści

1 The Occurrence and Cause of Auroras: a Short Introduction.- 1.1 Local Auroral Forms.- 1.1.1 Geometry.- 1.1.2 Intensity.- 1.1.3 The Local Auroral Display.- 1.2 Auroral Morphology.- 1.2.1 Magnetic Guiding of Auroral Particles; Coordinate Systems.- 1.2.2 Worldwide Auroral Morphology.- 1.2.3 Mid-Latitude Red Arcs.- 1.2.4 Polar Glow and Mantle Auroras.- 1.3 Particle Behaviour: Reflection, Absorption and Scattering.- 1.3.1 Mirror Effects.- 1.3.2 Absorption and Scattering of Particles in the Atmosphere.- 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.- 3.2.1 Auroral Protons, the Solar Wind and the Magnetosphere.- 3.2.2 The Proton Beam in the Atmosphere: Charge Exchange.- 3.2.3 The Proton Beam in the Atmosphere Diffusion.- 3.2.4 Excitation of the Hydrogen Lines.- 3.2.5 The Relation Between Hydrogen Lines and the First Negative N2+ Bands.- 3.2.6 The Hydrogen Line Profiles.- 3.2.7 Height Distribution of the Hydrogen Emissions.- 3.3 Observations on Hydrogen Lines.- 3.3.1 Techniques.- 3.3.2 The Intensity Ratio Between the Hydrogen Lines and the First Negative N2+ Bands.- 3.3.3 Absolute Intensities and Balmer Decrement.- 3.3.4 Geometry of Proton Aurora.- 3.3.5 Morphology of Proton Aurora.- 3.3.6 The Doppler Profiles.- References.- 4 The Optical Spectrum of Aurora.- 4.1 Description.- 4.1.1 Introduction.- 4.1.2 The Auroral Spectrum.- 4.1.3 Forbidden Atomic Emissions.- 4.1.4 Permitted Atomic Emissions.- 4.1.5 Molecular Emissions.- 4.1.6 The Intensity Distribution in the Spectrum.- 4.2 Local Variations in the Spectrum.- 4.2.1 Introduction.- 4.2.2 The I(5577)/I(1 neg)Ratio.- 4.2.3 Other Forbidden Emissions.- 4.2.4 Permitted Atomic Lines.- 4.2.5 Permitted Molecular Bands.- 4.3 Latitudinal and Zonal Variations.- References.- 5 Physics of the Optical Emissions.- 5.1 Excitation.- 5.1.1 Fast Particle Impact.- 5.1.2 Thermal Collisions.- 5.1.3 Excitation by Thermal Electrons.- 5.1.4 Discharge Mechanisms and Heating by Electric Fields.- 5.2 Deactivation.- 5.3 Interpretation of the Spectrum.- 5.3.1 Atomic Lines.- 5.3.2 The Intensity Distribution within Molecular Band Systems.- 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.- 7.2.1 Definition.- 7.2.2 Observations.- 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.