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The subject of geomagnetic micropulsations has developed extremely rapidly and it is difficult to know when is an appropriate time to pause and assess the sum total of our knowledge-both observational and theoretical. There has in recent years been a tremendous increase in both the quantity and quality of data and also many theoretical ad vances in our understanding of the phenomenon. Undoubtedly there will be further progress in both areas but it seems worthwhile now to review both our knowledge and our ignorance. This book was essen tially completed by the end of April 1969 and tries to give a summary of the subject up to that time. The Earth is enclosed in the magnetosphere, a hollow carved out of the solar wind by the Earth's magnetic field. Above the ionosphere there is a very tenuous thermal plasma of partially ionized hydrogen in diffusive equilibrium with magnetic and gravitational forces, and ener getic protons and electrons that constitute the trapped Van Allen ra diation belts. Throughout this anisotropic and inhomogeneous plasma, natural and man-made electromagnetic energy propagates in a wide variety of modes and frequency bands. This book is concerned with that class of natural signals called geomagnetic micropulsations-short period (usually of the order of seconds or minutes) fluctuations of the Earth's magnetic field.
Sommario
1 The Earth's Magnetic Field.- 1.1 Introduction.- 1.2 Transient Magnetic Variations.- 1.3 The Magnetosphere.- 1.4 Conjugacy.- References.- 2 The Morphology of Geomagnetic Micropulsations.- 2.1 Introduction.- 2.2 Classification of Micropulsations.- 2.3 Continuous Pulsations (Pc 1).- 2.4 Continuous Pulsations (Pc 2/3, Pc 4, and Pc 5).- 2.5 Pulsations with Irregular Forms.- References.- 3 Magneto-Hydrodynamic Waves.- 3.1 Alfvén Waves.- 3.2 The Equations of Small Hydromagnetic Oscillations.- 3.3 The Dispersion Relation.- 3.4 Theories of Pc Oscillations.- 3.5 Transmission of Hydromagnetic Waves Through the Ionosphere and Magnetosphere.- References.- 4 Theories of the Origin of Pc 1 Pulsations.- 4.1 Introduction.- 4.2 The Structure of the Frequency Spectrum of Pc 1's.- 4.3 The Cyclotron Instability Process and the Generation of Pc 1's.- 4.4 Sub Classes of Pc 1's-Non Linear Theories.- 4.5 Propagation of Pc 1's to Lower Latitudes.- References.- 5 Theories of Pc 2-5 and Pi Oscillations.- 5.1 Introduction.- 5.2 Toroidal Oscillations.- 5.3 The Excitation Mechanism of Pc 5's.- 5.4 Theories of Pi's.- References.- 6 Micropulsations and the Diagnostics of the Magnetosphere.- 6.1 Introduction.- 6.2 Relationship Between Micropulsations, The Solar Wind and the Dimensions of the Magnetosphere.- 6.3 Plasma Densities in the Magnetosphere Determined from Micropulsation Measurements.- 6.4 Micropulsations Observed in the Magnetosphere.- References.
