Introduction 1
1 Magnetic Reconnection 5
1.1 What is magnetic reconnection？ 5
1.1.1 Neutral points of a magnetic field 5
1.1.2 Reconnection in vacuum 7
1.1.3 Reconnection in plasma 8
1.1.4 Three stages in the reconnection process 11
1.2 Acceleration in current layers，why and how？ 13
1.2.1 The origin of particle acceleration 13
1.2.2 Acceleration in a neutral current layer 15
1.3 Practice：Exercises and Answers 19
2 Reconnection in a Strong Magnetic Field 21
2.1 Small perturbations near a neutral line 21
2.1.1 Historical comments 21
2.1.2 Reconnection in a strong magnetic field 22
2.1.3 A linearized problem in ideal MHD 26
2.1.4 Converging waves and the cumulative effect 28
2.2 Large perturbations near the neutral line 30
2.2.1 Magnetic field line deformations 31
2.2.2 Plasma density variations 34
2.3 Dynamic dissipation of magnetic field 34
2.3.1 Conditions of appearance 34
2.3.2 The physical meaning of dynamic dissipation 37
2.4 Nonstationary analytical models of RCL 38
2.4.1 Self-similar 2D MHD solutions 38
2.4.2 Magnetic collapse at the zeroth point 41
2.4.3 From collisional to collisionless reconnection 45
3 Evidence of Reconnection in Solar Flares 47
3.1 The role of magnetic fields 47
3.1.1 Basic questions 47
3.1.2 Concept of magnetic reconnection 48
3.1.3 Some results of observations 50
3.2 Three-dimensional reconnection in flares 51
3.2.1 Topological model of an active region 51
3.2.2 Topological portrait of an active region 55
3.2.3 Features of the flare topological model 57
3.2.4 The S-like morphology and eruptive activity 60
3.3 A current layer as the source of energy 63
3.3.1 Pre-flare accumulation of energy 63
3.3.2 Flare energy release 64
3.3.3 The RCL as a Partof an electric circuit 66
3.4 Reconnection in action 68
3.4.1 Solar flares of the Syrovatsky type 68
3.4.2 Sakao-type flares 69
3.4.3 New topological models 73
3.4.4 Reconnection between active regions 75
4 The Bastille Day 2000 Flare 77
4.1 Main observational properties 77
4.1.1 General characteristics of the flare 77
4.1.2 Overlay HXR images on magnetograms 79
4.1.3 Questions of interpretaion 82
4.1.4 Motion of the HXR kernels 83
4.1.5 Magnetic field evolution 84
4.1.6 The HXR kernels and field evolution 85
4.2 Simplified topological model 87
4.2.1 Photospheric field model.Topological portrait 87
4.2.2 Coronal field model.Separators 88
4.2.3 Chromospheric ribbons and kernels 89
4.2.4 Reconnected magnetic flux.Electric field 93
4.2.5 Discussion of topological model 96
5 Electric Currents Related to Reconnection 99
5.1 Magnetic reconnection in the corona 99
5.1.1 Plane reconnection model as a starting point 99
5.1.2 Three-component reconnection 105
5.2 Photospheric shear and coronal reconnection 107
5.2.1 Accumulation of magnetic energy 107
5.2.2 Flare energy release and CMEs 109
5.2.3 Flare and HXR footpoints 110
5.3 Shear flows and photospheric reconnection 114
5.4 Motions of the HXR footpoints in flares 117
5.4.1 The footpoint motions in some flares 117
5.4.2 Statistics of the footpoint motions 118
5.4.3 The FP motions orthogonal to the SNL 119
5.4.4 The FP motions along the SNL 120
5.4.5 Discussion of statistical results 123
5.5 Open issues and some conclusions 125
6 Models of Reconnecting Current Layers 129
6.1 Magnetically neutral current layers 129
6.1.1 The simplest MHD model 129
6.1.2 The current layer by Syrovatskii 131
6.1.3 Simple scaling laws 134
6.2 Magnetically non-neutral RCL 136
6.2.1 Transversal magnetic fields 136
6.2.2 The longitudinal magnetic field 137
6.3 Basic physics of the SHTCL 139
6.3.1 A general formulation of the problem 139
6.3.2 Problem in the strong field approximation 141
6.3.3 Basic local parameters of the SHTCL 142
6.3.4 The general solution of the problem 143
6.3.5 Plasma turbulence inside the SHTCL 145
6.3.6 Formulae for the basic parameters of the SHTCL 146
6.4 Open issues of reconnection in flares 149
6.5 Practice：Exercises and Answers 151
7 Reconnection and Collapsing Traps in Solar Flares 153
7.1 SHTCL in solar flares 153
7.1.1 Why are flares so different but similar？ 153
7.1.2 Super-hot plasma production 157
7.1.3 On the particle acceleration in a SHTCL 160
7.2 Coronal HXR sources in flares 160
7.2.1 General properties and observational problems 160
7.2.2 Upward motion of coronal HXR sources 162
7.2.3 Data on average upward velocity 163
7.3 The collapsing trap effect in solar flares 168
7.3.1 Fast electrons in coronal HXR sources 168
7.3.2 Fast plasma outflows and shocks 168
7.3.3 Particle acceleration in collapsing trap 171
7.3.4 The upward motion of coronal HXR sources 174
7.3.5 Trap without a shock wave 176
7.4 Acceleration mechanisms in traps 177
7.4.1 Fast and slow reconnection 177
7.4.2 The first-order Fermi-type acceleration 179
7.4.3 The betatron acceleration in a collapsing trap 180
7.4.4 The betatron acceleration in a shockless trap 183
7.5 Final remarks 184
7.6 Practice：Exercises and Answers 185
8 Solar-type Flares in Laboratory and Space 193
8.1 Solar flares in laboratory 193
8.1.1 Turbulent heating in toroidal devices 193
8.1.2 Current-driven turbulence in current layers 195
8.1.3 Parameters of a current layer with CDT 197
8.1.4 The SHTCL with anomalous heat conduction 198
8.2 Magnetospheric Physics Problems 200
8.2.1 Reconnection in the Earth Magnetosphere 200
8.2.2 MHD simulations of space weather 201
8.3 Flares in accretion disk coronae 202
8.3.1 Introductory comments 202
8.3.2 Models of the star magnetosphere 203
8.3.3 Power of energy release in the disk coronae 207
8.4 The giant flares 208
9 Particle Acceleration in Current Layers 211
9.1 Magnetically non-neutral RCLs 211
9.1.1 An introduction in the problem 211
9.1.2 Dimensionless parameters and equations 212
9.1.3 An iterative solution of the problem 214
9.1.4 The maximum energy of an accelerated particle 217
9.1.5 The non-adiabatic thickness of current layer 218
9.2 Regular versus chaotic acceleration 219
9.2.1 Reasons for chaos 220
9.2.2 The stabilizing effect of the longitudinal field 222
9.2.3 Characteristic times of processes 223
9.2.4 Dynamics of accelerated electrons in solar flares 224
9.2.5 Particle simulations of collisionless reconnection 225
9.3 Ion acceleration in current layers 226
9.3.1 Ions are much heavier than electrons 226
9.3.2 Electrically non-neutral current layers 227
9.3.3 Maximum particle energy and acceleration rates 229
9.4 How are solar particles accelerated？ 232
9.4.1 Place of acceleration 232
9.4.2 Time of acceleration 234
9.5 Cosmic ray problem 236
10 Structural Instability of Reconnecting Current Layers 237
10.1 Some properties of current layers 237
10.1.1 Current layer splitting 237
10.1.2 Evolutionarity of reconnecting current layers 239
10.1.3 Magnetic field near the current layer 240
10.1.4 Reconnecting current layer flows 241
10.1.5 Additional simplifying assumptions 242
10.2 Small perturbations outside the RCL 244
10.2.1 Basic assumptions 244
10.2.2 Propagation of perturbations normal to a RCL 244
10.2.3 The inclined propagation of perturbations 246
10.3 Perturbations inside the RCL 250
10.3.1 Linearized dissipative MHD equations 250
10.3.2 Boundary conditions 251
10.3.3 Dimensionless equations and small parameters 253
10.3.4 Solution of the linearized equations 255
10.4 Solution on the boundary of the RCL 258
10.5 The criterion of evolutionarity 260
10.5.1 One-dimensional boundary conditions 260
10.5.2 Solutions of the boundary equations 261
10.5.3 Evolutionarity and splitting of current layers 265
10.6 Practice：Exercises and Answers 266
11 Tearing Instability of Reconnecting Current Layers 269
11.1 The origin of the tearing instability 269
11.1.1 Two necessary conditions 269
11.1.2 Historical comments 270
11.2 The simplest problem and its solution 272
11.2.1 The model and equations for small disturbances 272
11.2.2 The external non-dissipative region 274
11.2.3 The internal dissipative region 276
11.2.4 Matching of the solutions and the dispersion relation 277
11.3 Physical interpretation of the instability 279
11.3.1 Acting forces of the tearing instability 279
11.3.2 Dispersion equation for tearing instability 281
11.4 The stabilizing effect of transversal field 282
11.5 Compressibility and a longitudinal field 285
11.5.1 Neutral current layers 285
11.5.2 Non-neutral current layers 287
11.6 The kinetic approach 288
11.6.1 The tearing instability of neutral layer 288
11.6.2 Stabilization by the transversal field 292
11.6.3 The tearing instability of the geomagnetic tail 293
12 Magnetic Reconnection and Turbulence 297
12.1 Reconnection and magnetic helicity 297
12.1.1 General properties of complex MHD systems 297
12.1.2 Two types of MHD turbulence 299
12.1.3 Helical scaling in MHD turbulence 301
12.1.4 Large-scale solar dynamo 302
12.2 Coronal heating and flares 304
12.2.1 Coronal heating in solar active regions 304
12.2.2 Helicity and reconnection in solar flares 305
12.3 Stochastic acceleration in solar flares 307
12.3.1 Stochastic acceleration of electrons 307
12.3.2 Acceleration of protons and heavy ions 309
12.3.3 Acceleration of 3He and 4He in solar flares 310
12.3.4 Electron-dominated solar flares 311
12.4 Mechanisms of coronal heating 313
12.4.1 Heating of the quiet solar corona 313
12.4.2 Coronal heating in active regions 315
12.5 Practice：Exercises and Answers 317
13 Reconnection in Weakly-Ionized Plasma 319
13.1 Early observations and classical models 319
13.2 Model of reconnecting current layer 321
13.2.1 Simplest balance equations 321
13.2.2 Solution of the balance equations 322
13.2.3 Characteristics of the reconnecting current layer 323
13.3 Reconnection in solar prominences 325
13.4 Element fractionation by reconnection 328
13.5 The photospheric dynamo 329
13.5.1 Current generation mechanisms 329
13.5.2 Physics of thin magnetic flux tubes 330
13.5.3 FIP fractionation theory 332
13.6 Practice：Exercises and Answers 334
14 Magnetic Reconnection of Electric Currents 339
14.1 Introductory comments 339
14.2 Flare energy storage and release 340
14.2.1 From early models to future investigations 340
14.2.2 Some alternative trends in the flare theory 344
14.2.3 Current layers at separatrices 345
14.3 Current layer formation mechanisms 346
14.3.1 Magnetic footpoints and their displacements 346
14.3.2 Classical 2D reconnection 348
14.3.3 Creation of current layers by shearing flows 350
14.3.4 Antisymmetrical shearing flows 352
14.3.5 The third class of displacements 354
14.4 The shear and reconnection of currents 355
14.4.1 Physical processes related to shear and reconnection 355
14.4.2 Topological interruption of electric currents 357
14.4.3 The inductive change of energy 357
14.5 Potential and non-potential fields 359
14.5.1 Properties of potential fields 359
14.5.2 Classification of non-potential fields 360
14.6 To the future observations by Solar-B 362
Epilogue 365
Appendix 1.Acronyms 367
Appendix 2.Notation 369
Appendix 3.Useful Formulae 371
Appendix 4.Constants 375
Bibliography 377
Index 407