Solar Flares

I. Introduction.- II. The Low-Temperature Flare.- 2.1. Flare Observations in the H? Line.- 2.1.1. The Flare Importance.- 2.1.2. Flares in Relation to Magnetic Fields.- A. Flare Positions Relative to Sunspots and Plages.- B. Flare Positions in the Magnetic Field.- C. Flare-Associated Changes in the Magnetic Field.- C.l. Old-Type Measurements.- C.2. High-Resolution Measurements.- C.3. Mathematical Models of Coronal Magnetic Fields.- C.4. Other Methods.- C.5. Summary.- 2.1.3. Motions in Flares.- A. Slow Ascent.- B. Rise and Fall.- C. High-Speed Ejections.- D. Rotation Effects.- E. Expansion of Flare Ribbons.- F. Fast Expansion.- G. In-Fall Motions.- 2.2. Flare Spectra.- 2.2.1. Characteristic Features of the Flare Spectrum.- 2.2.2. Method of Analysis of Hydrogen Lines.- 2.2.3. Line Broadening.- 2.2.4. Electron Density.- A. Electron Density in Disc Flares.- B. Electron Density in Limb Flares.- 2.2.5. The Optical Thickness.- 2.2.6. Electron Temperature.- 2.2.7. The Filamentary Structure of Flares.- 2.2.8. Hydrogen Density.- 2.2.9. Line Asymmetry.- 2.2.10. Differences between Prominences and Limb Flares.- 2.2.11. Continuous Emission.- A. Synchrotron Radiation.- B. Particle Penetration to Low Atmospheric Layers.- C. Heating of Upper Photosphere.- D. White-Light Flare Wave.- 2.3. Models of Chromospheric Flares.- 2.3.1. Models of Energy Transfer from the Corona.- A. Brown’s Model.- B. Model by Shmeleva and Syrovatsky.- C. Models Including both Conduction and Particle Heating.- D. Models by Canfield and Athay.- 2.3.2. Model by Machado and Linsky.- A. The Photospheric Flare.- B. The Chromospheric Flare.- III. The High-Temperature Flare.- 3.1. Thermal Phenomena.- 3.1.1. Coronal Condensations.- 3.1.2. Soft X-Ray Emission.- A. Soft X-Ray Bursts.- B. X-Ray Flares.- C. Indirect Observations of Solar X-Rays.- 3.1.3. Flare Spectrum in the X-Ray Region.- A. The Continuous Emission.- B. The Line Emission.- 3.1.4. Temperature in the X-Ray Flare.- A. Temperature and Emission Measure.- B. Line Excitation.- C. Flare Cooling.- 3.1.5. Electron Density in the X-Ray Flare.- 3.1.6. Gradual Microwave Bursts.- 3.2. Non-Thermal Phenomena.- 3.2.1. Hard X-Ray Bursts.- A. Characteristic Properties of the Hard X-Ray Bursts.- B. Evidence on the Non-Thermal Nature of the Hard X-Ray Bursts.- C. Theoretical Interpretation of the Hard X-Ray Bursts.- D. Models of Impulsive and Continuous Acceleration.- E. Thin-Target and Thick-Target Emission.- 3.2.2. EUV Bursts.- 3.2.3. Impulsive Microwave Bursts.- A. Characteristic Properties.- B. Interpretation of the Impulsive Microwave Bursts.- C. Controversy with the Theory of Hard X-Ray Bursts.- 3.2.4. Type IV Bursts.- A. Type IVmA Bursts.- B. Type IVmB Bursts.- C. Type IVdm Bursts and Radio Pulsations.- D. Type IV Burst Spectrum.- 3.2.5. Type II Bursts.- 3.2.6. Type III Bursts.- A. Type III Burst Occurrence.- B. Properties of Type III Bursts.- C. Interpretation of Type III Bursts.- D. Type U Bursts.- E. Type V Bursts.- IV. Flare-Associated Optical Phenomena.- 4.1. Pre-Flare Filament Activation.- 4.2. Surges and Sprays.- 4.2.1. Surges.- 4.2.2. Sprays.- 4.3. Flare Waves.- 4.3.1. The Wave Fronts.- 4.3.2. Disparitions Brusques.- 4.4. Loop Prominences.- V. Particle Emission from Solar Flares.- 5.1. Solar Protons.- 5.1.1. Cosmic-Ray and Proton Flares.- A. Characteristics of the Flare on the Sun.- B. Characteristics of the Active Region.- C. Complexes of Activity.- D. Time Variations in the Proton Flare Occurrence.- 5.1.2. Satellite-Sensed Events.- 5.1.3. The Energy Spectrum.- A. The Propagation Effects.- B. The Storage Effects.- C. The Size of an Event.- 5.2. Heavier Nuclei.- 5.3. Solar Electrons.- 5.3.1. Non-Relativistic Electrons.- A. The Event Occurrence and the Associated Flares.- B. Proton-Electron and Pure Electron Events.- C. Time of Acceleration.- 5.3.2. Relativistic Electrons.- 5.4. Nuclear Reactions in Flares.- 5.4.1. Accelerated Isotopes of Hydrogen and Helium.- 5.4.2. Neutrons.- 5.4.3. ?-Rays.- 5.5. Particle Clouds and Interplanetary Shock Waves.- 5.5.1. Characteristic Properties of Interplanetary Shocks.- 5.5.2. Shock-Wave-Associated Variations in the Particle Flux.- 5.5.3. Increased Helium Content behind Interplanetary Shock Waves.- VI. Flare Models.- 6.1. Basic Properties of Flares.- 6.2. Synthesis of a Flare.- A. Pre-Flare Phase.- B. Quasi-Thermal Flare.- C. Impulsive Flare.- D. Electron Flare.- E. Proton Flare.- F. Problems.- 6.3. The Energy Source.- 6.4. The Energy Storage.- 6.4.1. Alfvén Waves as the Source of Flares.- 6.4.2. Models with a Passive Role for the Magnetic Field.- A. Elliot’s Model.- B. Schatzman’s Model.- C. Carmichael’s Model.- D. Pneuman’s Model.- E. Model by Sen and White.- 6.4.3. Models with an Active Role for the Magnetic Field.- A. Model by Gold and Hoyle.- B. Model by Alfvén and Carlqvist.- C. Sheared Fields.- D. Force-Free Flare Build-up.- E. Current Sheets.- 6.5. The Energy Release.- 6.5.1. Models without a Current Sheet.- A. Piddington’s Model.- B. Elliot’s Model.- C. Kahler and Kreplin’s Model.- D. Evaporating Flare Models.- E. Alfvén and Carlqvist’s Model.- 6.5.2. Current Sheet Models.- A. Priest and Heyvaerts’ Model.- B. Sturrock’s Model.- C. Similarities with Magnetospheric Substorms.- D. Pustilnik’s Model.- 6.5.3. Syrovatsky’s Model.- A. The Pre-Flare Activation.- B. The Thermal Phase.- C. The impulsive Phase.- D. Deficiencies of Syrovatsky’s Theory.- 6.6. The Particle Acceleration.- 6.6.1. Current Interruption.- 6.6.2. Fermi Mechanism.- 6.6.3. Stochastic Acceleration.- References.- Index of Subjects.