2 Solar models: structure, neutrinos and helioseismological properties 8 J.N. Bahcall, S. Basu and M.H. Pinsonneault

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1 Foreword xv E.N. Parker 1 Dynamic Sun: an introduction 1 B.N. Dwivedi 1.1 Introduction Main contents Concluding remarks 7 2 Solar models: structure, neutrinos and helioseismological properties 8 J.N. Bahcall, S. Basu and M.H. Pinsonneault 2.1 Introduction Standard solar model Variant and deviant solar models Neutrino physics Standard model Calculated uncertainties NACRE charged particle fusion rates Variant and deviant models The electron number density Sound speeds Discussion and summary Standard solar model: current epoch Neutrino fluxes and related quantities 29 v

2 vi Sound speeds 31 References 32 3 Seismic Sun 36 S.M. Chitre and H.M. Antia 3.1 Introduction Structure equations and the Standard Solar Model Seismology of the Sun Inferences about the solar structure 41 References 52 4 Rotation of the solar interior 55 J. Christensen-Dalsgaard and M.J. Thompson 4.1 Introduction Helioseismic probes of the solar interior Rotational effects on the oscillation frequencies Data on rotational splitting Inversion for solar internal rotation The solar internal rotation Rotation of the solar convection zone The tachocline The radiative interior Modelling solar rotation Final remarks 73 References 74 5 Helioseismic tomography 78 A.G. Kosovichev 5.1 Introduction Method of helioseismic tomography The ray approximation The Born approximation Inversion methods Diagnostics of supergranulation Large-scale flows Meridional circulation Emerging active regions Structure and dynamics of sunspots 93

3 vii 5.11 Imaging the far side of the Sun Conclusion 99 References The solar dynamo as a model of the solar cycle 103 A.R. Choudhuri 6.1 Introduction Relevant observations Some basic MHD considerations The turbulent dynamo and mean field MHD Dynamo in the overshoot layer? The Babcock Leighton approach and advective dynamo models Miscellaneous ill-understood issues Conclusion 123 References Spectro-polarimetry 128 J.O. Stenflo 7.1 Remote sensing of the Sun s magnetic field: an introduction Observational techniques and their limitations Zeeman-effect diagnostics The Hanle effect Optical pumping Concluding remarks 146 References Solar photosphere and convection 148 Å. Nordlund 8.1 Introduction Dynamic and thermal properties of the solar photosphere Spectral line synthesis P-mode diagnostics Large scale velocity fields Consequences for coronal and chromospheric heating 162

4 viii 8.7 Concluding remarks 162 References The dynamics of the quiet solar chromosphere 165 W. Kalkofen, S.S. Hasan and P. Ulmschneider 9.1 Introduction Oscillations in the nonmagnetic chromosphere Oscillations in the magnetic network 172 References Heating of the solar chromosphere 181 P. Ulmschneider and W. Kalkofen 10.1 Introduction Empirical chromosphere models Energy balance and the necessity of mechanical heating Overview of the heating mechanisms Search for the important heating mechanisms Summary and outlook 193 References The solar transition region 196 O. Kjeldseth-Moe 11.1 Introduction Emission from the transition region plasma The emitted intensity Underlying approximations and concepts Constant conductive flux and the thin transition region The extended transition region Excess emission at temperatures below 10 5 K The EUV flash spectrum: direct observation of an inhomogeneous transition region A transition region structured by the magnetic field Spicules and the transition region An extremely fine structured transition region? Unresolved fine structures Unresolved dynamic evolution? The redshifted transition region Line shifts in the transition region 205

5 ix Red- or blueshifts from siphon flows and spicules? Red shifts as signatures of downward propagating waves The dynamic and time dependent transition region Morphology of transition region loops Velocities in transition region loops Rapid time changes in the emission Conclusion anewconcept for the transition region 212 References Solar Magnetohydrodynamics 217 E.R. Priest 12.1 Introduction Magnetohydrodynamic equations Flux tubes Basic equations Induction equation The Lorentz force Magnetohydrostatics Introduction Potential fields Force-free fields Magnetic flux tubes Magnetohydrodynamic waves Sound waves Alfvén waves Compressional Alfvén waves Magnetoacoustic waves Shock waves Concluding comment 237 References Solar activity 238 Z. Švestka 13.1 Solar cycles Active regions Complexes of activity and interconnecting loops Surges, jets, and sprays Solar flares 245

6 x 13.6 Coronal mass ejections and coronal storms Relation between CMEs and flares Other sources of CMEs Causes of instabilities Accelerated particles Impacts of solar activity at the Earth 257 References Particle acceleration 262 A.G. Emslie and J.A. Miller 14.1 Introduction Observational constraints Electrons Ions Direct electric field acceleration Stochastic acceleration The cascading turbulence model Baseline case Conclusions 285 References Radio observations of explosive energy releases on the Sun 288 M.R. Kundu and S.M. White 15.1 Introduction Flare studies Millimeter flare emission: comparison with microwave and hard X-rays/gamma rays Time profiles of millimeter bursts Observations of millimeter and microwave bursts Simple spiky bursts in microwaves Microwave and hard X-ray observations of footpoint- emission from flaring loops Double loop configuration of flaring regions Modeling of microwave flares Small scale energy releases on the Sun XBP flares Metric type III burst emission from an XBP flare in a coronal hole Microwave observations of XBP flares 301

7 xi Radio observations of coronal X-ray jets Meterwave observations of jets A statistical study of jets in microwaves Active region transient brightenings (ARTB s) Radio (VLA) observations Radio (Nobeyama) observations Radio (OVRO) observations Transient brightenings in quiet Sun regions Implications of transients for coronal heating Concluding remarks 310 References Coronal oscillations 314 V.M. Nakariakov 16.1 Introduction The method of MHD coronal seismology Detectability of MHD waves in the corona Compressive waves in polar plumes Observations Interpretation as slow magnetoacoustic waves Search for Alfvén waves Theoretical aspects Observational aspects Compressive waves in long loops Observations and interpretation Seismologic implications Flare-generated oscillations of coronal loops Observations Determination of the magnetic field Determination of transport coefficients EIT or coronal Moreton waves Conclusions 332 References Probing the Sun s hot corona 335 K.J.H. Phillips and B.N. Dwivedi 17.1 The solar corona The spacecraft era 338

8 xii 17.3 Heating of the corona: theory Observational evidence: transient brightenings Physical characteristics of the corona Observational evidence: wave motions Conclusions 351 References Vacuum-ultraviolet emission line diagnostics for solar plasmas 353 B.N. Dwivedi, A. Mohan and K. Wilhelm 18.1 The Sun in the ultraviolet emission lines SUMER spectrograph Atomic processes Emission lines Coronal model approximation Electron collisional excitation and de-excitation Proton collisional excitation and de-excitation Ionization balance Plasma diagnostics Emission measure analysis Electron-density diagnostics Electron-temperature diagnostics Abundance determination Some new results from SUMER Coronal holes and the solar wind The red/blue Sun Explosive events Sunspot transition region oscillations Solar flare observed by SUMER Conclusions 370 References Solar wind 374 E. Marsch, W.I. Axford and J.F. McKenzie 19.1 The solar wind Basic energy considerations Historic restrospective: Parker s model Problems with a polytropic single-fluid model 375

9 xiii Energy requirements on heavy ions Solar corona and wind in three dimensions Types of solar wind Three-dimensional solar corona Electron density and temperature Fast solar wind Coronal and in-situ observations Basic model equations Heating functions Some results from model calculations The wave spectrum: origin, evolution and dissipation Critical issues in the models Slow solar wind Observations of slow flows Models of the closed corona and slow wind Sources of the solar wind Chromospheric network Network pico-flares Heating of the quiet corona Some consequences of network flares Problems Problems with the observations Problems with the theory Conclusions 399 References Solar observing facilities 403 B. Fleck and C.U. Kelller 20.1 Introduction Ground-based instruments Present General purpose telescopes Synoptic telescopes Synoptic networks Synoptic radio telescopes Future plans General purpose telescopes Synoptic telescopes 415

10 xiv Radio telescopes Current and planned suborbital missions Space missions In operation Ulysses Yohkoh Wind SOHO ACE TRACE GOES/Solar X-ray imager CORONAS-F Genesis HESSI In development and under study Solar-B STEREO Space Solar Telescope SST SDO Solar Orbiter Solar probe Solar sentinels Conclusions 432 References 432 Index 435