Structure and Development of Solar Active Regions

K. O. KIEPENHEUER ( Fraunhofer Institut, Freiburg i. Br., Germany) The present symposium, to my knowledge the largest ever held in the field of solar research (170 astronomers from 21 countries) was held in the building of the Hun­ garian Academy of Sciences in Budapest from September 4 to 8, 1967. It was the 35th symposium organized and sponsored by the International Astronomical Union. The majority of participants were financedfrom national sources. The Organizing Commit­ tee consisted of K. O. Kiepenheuer (Chairman), L. Davis, L. Dezso (Local Organizer), A.D. Fokker, R. Michard, A.B. Severny, H.J. Smith, Z. Svestka, and H. Tanaka. In order to ensure prompt publication, the manuscripts had to be supplied by the authors 1 month after the meeting. The discussions have been recorded on tape. Their reproduction in this book, however, is based almost completely on the contributors' writing down their comments and questions on the spot. Two special projects have been reported and discussed shortly during the sym­ posium: The world wide project 'Cooperative Study of Solar Active Regions' (CSSAR) organized by Dr. R. Michard, under the auspices of the IAU, which has put at the disposal of our solar community a precious observing material on Active Regions over a period of 6 months.

Welcome by the Hungarian Academy of Sciences.- Preface and introduction.- I General Development of an Active Region.- Patterns of active region magnetic field development.- Origine des régions actives solaires ‘anormales’.- Magnetic classification of active regions.- Development of magnetic fields in active regions.- The balance of magnetic fluxes in active regions.- On the birth of some proton-flare regions.- Some patterns in the development of centers of solar activity, 1962-66.- Last phases of development of active regions.- On some properties of the velocity field in a developed active region.- The migration of sunspot activity along solar meridians and parallels.- Chromospheric explosions and satellite sunspots.- Study of an active region of the Sun during three rotation periods.- II Theoretical Aspects.- Magnetohydrodynamics of an active region.- Concentration of magnetic fields in the deep convection zone.- Oscillatory modes of energy transport in solar magnetic regions.- On the magnetic structure of an active region.- Oscillatory convection in strong magnetic fields and origin of active regions.- Quantitative estimations of the anomalous plasma diffusion in an active region.- Étude critique d’un champ ‘current-free’ dans l’atmosphère solaire.- Sunspots and magnetohydrodynamic flows.- III Optical Structure of an Active Region.- On the state of the photosphere before the appearance of sunspots.- Correlations between brightness fields and magnetic fields on the Sun.- The supergranular pattern and the stable stages of sunspot groups.- The intensity, velocity and magnetic structure in and around a sunspot.- Fine structure of brightness, velocity and magnetic field in the penumbra.- Concerning the development of the Evershed motion in sunspots.- The connection of fine-structure photospheric features in active regions with magnetic fields.- On the magnetic-field configuration in sunspots.- The proper motions of sunspots and the magnetic field of active regions.- Fluctuations of the magnetic-field strength of sunspots within one day.- On the structure of the magnetic field of sunspots.- Magnetic and Doppler oscillations in active regions.- Preliminary communication on the short-period oscillations of solar magnetic fields.- Some comments about correlations between magnetic field and velocity, magnetic field and line intensity in the undisturbed photosphere.- On some spectrographic observations related to the structure with height of active regions and particularly solar flares.- Chromospheric heights in active regions.- The structure of the lower solar chromosphere in undisturbed and active regions.- Problems in the interpretation of polarization measurements in active regions.- On the magnetic-field structure around filaments.- The formation, structure and changes in filaments in active regions.- Prominences in active regions.- The ‘detwisted’ prominence of September 12, 1966.- Loop-prominence systems and proton-flare active regions.- Bright points (moustaches) and arch filaments in young active regions.- Solar active regions in Mg II light.- IV Cooperative Study of Solar Active Regions (CSSAR).- Introductory report.- Flare activity and spotgroup development.- A study of the localization of flares in selected active regions.- Evolution of Ca plages of the CSSAR active regions.- Correlation between Ca plages and longitudinal magnetic fields of the CSSAR active regions.- Évolution des émissions coronales au cours de la vie d’un centre actif.- V Coronal and Interplanetary Structure of an Active Region.- Observation des jets et concentrations d e la couronne au-dessus des régions actives.- Influence of magnetic fields on the structure of the solar corona.- Photographs of coronal streamers from a rocket on May 9, 1967.- New aspects of the role of development and structure of solar active regions in the arrangements of the corona based on its geomagnetic displays.- Active regions and the interplanetary magnetic field.- Extreme ultraviolet observations of active regions in the solar corona.- Protons associated with centres of solar activity and their propagation in interplanetary magnetic-field regions co-rotating with the Sun.- The solar corona above active regions: a comparison of extreme ultraviolet line emission with radio emission.- On some aspects of XUV spectroheliograms.- La composante lentement variable des rayons X solaires en relation avec la structure des centres d’activité.- X-radiation studies of the corona.- Observations of energetic X-rays from quiescent solar active regions.- X-ray picture of the Sun taken with Fresnel zone plates.- The significance of the polarization of solar short- wavelength X-rays.- VI Transient Phenomena.- Analysis of some solar flares from optical. X-ray, and radio observations.- Interaction of magnetic fields and the origin of proton flares.- A model of solar flares.- The high-energy flare plasma.- The occurrence and possible meaning of the ‘nimbus’.- Flare-produced coronal waves.- The observation of 10-50 KeV solar flare X-rays by the OGO satellites and their correlation with solar radio and energetic particle emission.- VII Proton Flare Project (PFP).- and summary.- Observations of the solar proton event of August 28, 1966.- Sunspot changes following proton flares.- VIII Radio Structure of an Active Region.- Homology of solar radio events.- Some results on solar activity at 408 MHz.- Conditions of acceleration of solar electrons, and determination of the magnetic field in the high corona from the characteristics of a type-IV burst.- Tendencies to repeating of type-IVm bursts and their relations to the stage of development of the sunspot group.- Properties of sources of the slowly varying component of 2 cm solar radio emission.- Some properties of the sources of slowly varying and component and of bursts at 612 Mc/s.- Satellite observations of solar radio bursts.- Comparison of 8-mm solar radio features with local magnetic fields and chromospheric features.- Radio emission of spotgroups.- Quelques relations entre sursauts radioélectriques solaires sur ondes décimétriques et caractères mor-phologiques des éruptions chromosphériques associées.- The effect of compression and expansion of plasma on the generation of synchrotron radiation.- The great burst of May 23, 1967.- Summarizing Review.- The development and structure of an active region.