Solar System Magnetic Fields

In September 1984 a Summer School on Solar System Plasmas was held at Imperial College with the support of the Science and Engineering Research Council. An excellent group of lecturers was assembled to give a series of basic talks on the various aspects of the subject, aimed at Ph. D. students or researchers from related areas wanting to learn about the plasma physics of the solar system. The students were so appreciative of the lectures that it was decided to write them up as the present book. Traditionally, different areas of solar system science, such as solar and magnetospheric physics, have been studied by separate communities with little contact. However, it has become clear that many common themes cut right across these distinct topics, such as magnetohydrodynamic instabilities and waves, magnetic reconnect ion , convection, dynamo activity and particle acceleration. The plasma parameters may well be quite different in the Sun's atmosphere, a cometary tailor Jupiter's magnetosphere, but many of the basic processes are similar and it is by studying them in different environments that we come to understand them more deeply. Furthermore, direct in situ measurements of plasma properties at one point in the solar wind or the magnetosphere complement the more global view by remote sensing of a similar phenomenon at the Sun.

1 Introduction to Solar Activity.- 1.1 Some Basic Properties of the Sun.- 1.2 Basic Equations of Magnetohydrodynamic.- 1.2.1 Magnetohydrostatics.- 1.2.2 Waves.- 1.2.3 Instabilities.- 1.3 Sunspots.- 1.4 Prominences.- 1.4.1 Prominence Formation.- 1.4.2 Magnetostatic Support.- 1.5 The Corona.- 1.5.1 Models of the Corona.- 1.5.2 Coronal Heating.- 1.6 Solar Flares.- 1.7 Conclusion.- References.- 2 An Introduction to Magnetospheric MHD.- 2.1 Introduction.- 2.2 Why is There a Magnetosphere?.- 2.3 The Open Magnetosphere Morphology.- 2.4 Momentum Transfer.- 2.5 Magnetospheric Substorms.- 2.6 Magnetohydrodynamic Waves.- References.- 3 Magnetohydrodynamic Waves.- 3.1 Structuring and Stratification.- 3.2 Waves in a Magnetically Structured Atmosphere.- 3.3 Waves in a Uniform Medium.- 3.3.1 The Alfvén Wave.- 3.3.2 Magnetoacoustic Waves.- 3.4 Waves in Discretely Structured Media.- 3.4.1 Incompressible Medium.- 3.4.2 Compressible Medium.- 3.5 Oscillations in a Low ?-Gas.- 3.5.1 Slab Inhomogeneities.- 3.5.2 Cylindrical Inhomogeneities.- 3.5.3 Impulsively Generated Fast Waves.- 3.6 Damped Alfvén Waves.- 3.7 Waves in Stratified Atmospheres.- 3.7.1 Sound Waves.- 3.7.2 The Influence of a Horizontal Magnetic Field.- 3.8 Slender Flux Tubes.- 3.8.1 The Slender Flux Tube Equations: Sausage Modes.- 3.8.2 Pulse Propagation.- 3.8.3 Kink Modes.- 3.8.4 Instabilities in Tubes.- References.- 4 MHD Instabilities.- 4.1 Equilibrium Solutions.- 4.1.1 Introduction.- 4.1.2 Energetics.- 4.1.3 The Lorentz Force.- 4.1.4 Magnetohydrostatic (MHS) Equilibria.- 4.1.5 Cylindrically Symmetric Magnetic Fields.- 4.1.6 2-Dimensional Magnetic Fields.- 4.2 Physical Description of MHD Instabilities.- 4.3 Linearised MHD Equations.- 4.4 Normal Modes Method.- 4.5 Energy (or Variational) Method.- 4.6 The Rayleigh-Taylor Instability.- 4.6.1 Normal Modes — Two Fluids.- 4.6.2 Normal Modes — Continuous Fluid.- 4.6.3 Simple Energy Method — Two Fluids.- 4.6.4 Energy Method — Continuous Fluids.- 4.6.5 MHD Incompressible Rayleigh-Taylor Instability.- 4.7 The Sharp Pinch — Normal Modes.- 4.7.1 Inner Solution r < a.- 4.7.2 Outer Solution r > a.- 4.7.3 Matching Conditions at r = a.- 4.8 General Cylindrical Pinch — Energy Method.- 4.8.1 Minimisation of ?2W.- 4.8.2 Suydam’s Criterion — A Necessary Condition.- 4.9 Necessary and Sufficient Conditions — Newcomb’s Analysis.- 4.10 Resistive Instabilities — Tearing Modes.- 4.10.1 Introduction.- 4.10.2 The Analysis of FKR.- 4.11 Applications of MHD Instabilities.- 4.11.1 Introduction.- 4.11.2 Ideal Kink Instability of Coronal Loops.- 4.11.3 Two-Ribbon Flares.- References.- 5 Magnetic Reconnect.- 5.1 Introduction.- 5.2 Reconnection: What It Is and What It Does.- 5.3 Fluid (MHD) Models of Reconnection.- 5.4 The Single-Particle Approach in a Collision-Free Plasma.- References.- 6 Magnetoconvection.- 6.1 Small Flux Tubes.- 6.2 Convection in a Strong Magnetic Field.- 6.3 Structure of the Large-Scale Magnetic Field.- References.- 7 Aspects of Dynamo Theory.- 7.1 The Homopolar Disc Dynamo.- 7.2 The Stretch-Twist-Fold Dynamo.- 7.3 Behaviour of the Dipole Moment in a Confined System.- 7.4 The Pros and Cons of Dynamo Action.- 7.5 Flux Expulsion and Topological Pumping.- 7.6 Mean-Field Electrodynamics.- 7.7 Some Properties of the Pseudo-Tensors ?ij and ?ijk.- 7.8 The Solar Dynamo.- 7.9 Magnetic Buoyancy as an Equilibration Mechanism.- References.- 8 Solar Wind and the Earth’s Bow Shock.- 8.1 The Solar Wind as a Fluid.- 8.1.1 Fluid Models of the Solar Wind.- 8.1.2 Solar Wind Magnetic Fields.- 8.1.3 Mass and Angular Momentum Loss.- 8.1.4 Refinements of Fluid Models.- 8.2 The Solar Wind as a Plasma.- 8.2.1 Why a Plasma Description is Needed.- 8.2.2 Solar Wind Protons.- 8.2.3 Minor Ions in the Solar Wind.- 8.2.4 Waves in the Solar Wind.- 8.3 The Earth’s Bow Shock.- 8.3.1 Why a Shock is Needed.- 8.3.2 General Shock Considerations.- 8.3.3 Macroscopic Fields at Collisionless Shocks.- 8.3.4 Particle Dynamics at Collisionless Shocks — Electrons.- 8.3.5 Particle Dynamics at Collisionless Shocks — Ions.- 8.3.6 The Global Structure of the Earth’s Bow Shock and Foreshock.- 8.4 Conclusion.- References.- 9 Planetary Magnetospheres.- 9.1 Comparative Theory of Magnetospheres.- 9.1.1 Obstacles in a Flowing Plasma.- 9.1.2 Plasma Sources.- 9.1.3 Magnetospheric Flows.- 9.2 Planetary Magnetospheres.- 9.2.1 Mercury.- 9.2.2 Venus.- 9.2.3 Earth.- 9.2.4 Mars.- 9.2.5 Jupiter.- 9.2.6 Saturn.- 9.2.7 Uranus.- 9.2.8 Neptune and Pluto.- 9.3 Conclusions.- References.- 10 Comets.- 10.1 Introduction to Comet Structure.- 10.2 Interaction between the Solar Wind and the Comet.- 10.3 Production of Neutral Gas.- 10.3.1 Vaporisation.- 10.3.2 Neutral Gas Density.- 10.4 Ionisation.- 10.4.1 Ionisation Processes.- 10.4.2 Size of the Coma.- 10.5 Ion Pick-Up.- 10.5.1 Ion Pick-Up Trajectories.- 10.5.2 Stability of the Distribution.- 10.6 Principal Plasma Regimes.- 10.6.1 Main Regions.- 10.6.2 The Contact Surface.- 10.6.3 Bow Shock.- 10.7 Magnetohydrodynamic Flow at a Comet.- 10.7.1 Numerical Solution of the MHD Equations.- 10.7.2 Validity of the MHD Approach.- 10.8 Special Features of the Morphology.- 10.8.1 Rays, Tail Streamers.- 10.8.2 Disconnection Events.- 10.8.3 Dusty Plasmas.- 10.9 Conclusion.- References.