ENERGETIC PHENOMENA ON THE SUN ASTROPHYSICS AND SPACE SCIENCE LIBRARY A SERIES OF BOOKS ON THE RECENT DEVELOPMENTS OF SPACE SCIENCE AND OF GENERAL GEOPHYSICS AND ASTROPHYSICS PUBLISHED IN CONNECTION WITH THE JOURNAL SPACE SCIENCE REVIEWS Editorial Board R. L. F. BOYD, University College, London, England W. B. BURTON, Sterrewacht, Leiden, The Netherlands C. DE JAGER, University 0/ Utrecht, The Netherlands J. KLECZEK, Czechoslovak Academy o/Sciences, Ondfejov, Czechoslavakia Z. KOPAL, University o/Manchester, England R. LOST, European Space Agency, Paris, France L.I. SEDOV,Academy o/Sciences o/the U.S.S.R., Moscow, U.S.SR. Z. SVESTKA, Laboratory for Space Research, Utrecht, The Netherlands VOLUME 153 CURRENT RESEARCH ENERGETIC PHENOMENA ON THE SUN Edited by M. R. KUNDU Astronomy Program, University ofM aryland at College Park, Maryland, U.S.A. B. WOODGATE NASA/Goddard Space Flight Center, Greenbelt, Maryland, U.S.A. and E. J. SCHMAHL Astronomy Program, University ofM aryland at College Park, Maryland, U.S.A . .. KLUWER ACADEMIC PUBLISHERS DORDRECHT / BOSTON / LONDON Library of Congress Cataloging in Publication Data Energetic phenomena on the sun I edited by Mukul R. Kundu and Bruce Woodgate, and E.J. Schmahl. p. cm. -- (Astrophysics and space science library; 153) "A result of three meetings ... held at the Goddard Space Flight Center on January 24-28, 1983, June 8-14, 1983, and February 13-17, 1984"--Foreword. Includes bibliographies and index. ISBN 0-7923-0172-2 1. Solar flares--Congresses. I. Kundu, Mukul Ranjan, 1930- II. Woodgate, Bruce. III. Schmahl, E. J. IV. Series: Astrophysics and space science library; v. 153. QB526.F6E52 1989 523.7·5--dcI9 89-31037 ISBN-13:978-94-010-7548-0 e-ISBN-13:978-94-009-2331-7 DOl: 10.1 007/978-94-009-2331-7 Published by Kluwer Academic Publishers, P.O. Box 17,3300 AA Dordrecht, The Netherlands. Kluwer Academic Publishers incorporates the publishing programmes of D. Reidel, Martinus Nijhoff, Dr W. Junk and MTP Press. Sold and distributed in the U.S.A. and Canada by Kluwer Academic Publishers, 101 Philip Drive, Norwell, MA 02061, U.S.A. In all other countries, sold and distributed by Kluwer Academic Publishers Group, P.O. Box 322, 3300 AH Dordrecht, The Netherlands. printed on acid/ree paper All Rights Reserved © 1989 by Kluwer Academic Publishers Softcover reprint of the hardcover 1s t edition 1989 No part of the material protected by this copyright notice may be reproduced or utilized in any form or by any means, electronic or mechanical including photocopying, recording or by any information storage and retrieval system, without written permission from the copyright owner. TABLE OF CONTENTS FOREWORD.. • • • • . • . . • • . • •• • • . . •• • . • . . • • . • • • . •• • •• • •• • • . • . • . • . . . • • . • •. ix INTRODUCTION. • • • • . . • • . . • • • • • • . • • • . • • • • . • • • • • • • • • • • . • • • . . • . • • • • • • . .• xii i CHAPTER 1: PREFLARE ACTIVITy ••••••••••••••.••.••••••..•.••..••..•• 1 • 1 INTRODUC TION. . • . • . • • . • • • . . • • . . . • • • . . • • . . . . • • • . . • . . • • • . • • . . • • • 7 1.2 MAGNETOHYDRODYNAMIC INSTABILITy.............................. 11 1.3 PREFLARE MAGNETIC AND VELOCITY FIELDS........................ 30 1.4 CORONAL MANIFESTATIONS OF PREFLARE ACTIVITy.................. 77 1 .5 REFERENCES. . • • . . • • • . • • • . • • • • • • • • • • • • . . . • • • . . • . • . • . • . • • . . • . . • • 112 CHAPTER 2: PARTICLE ACCELERATION •••••.•••..••••...•••..••••.••.•.• 127 2.1 INTRODUC TION. • • . • . • • • • • • • . • . . • • • • • . • . . • • • • • • . • • . . • . . . . . . • • . • • 13 1 2.2 PHENOMENA ASSOCIATED WITH MILDLY-RELATIVISTIC ELECTRONS ....•. 133 2.3 PHENOMENA ASSOCIATED WITH IONS AND RELATIVISTIC ELECTRONS IN SOLAR FLARES. • . • . . • • • . • • • • • . • • . • . • • • • • • • • • • • • • • • • • • • • • • • • • 178 2.4 THEORETICAL STUDIES OF PARTICLE ACCELERATION ••••••••••....•• 197 2.5 ACHIEVEMENTS - OUTSTANDING QUESTIONS •......•.••..•...••.•.... 212 2.6 ACKNOWLEDGEMENTS. . . . . . . • • • . . • • • • • • • . • • • . . . • • • • . • . . . . • • • • . • • . . 215 2.7 REFERENCES. • • . • . . • . . . • . . • • • . • . • • • • • • • . • • . . . • • • . • • . • • • • • • . . • . . 216 CHAPTER 3: IMPULSIVE PHASE TRANSPORT ••••...•....••..•.••.•••..••.. 225 3.1 INTRODUCTION................................................. 229 3.2 IMPULSIVE PHASE OBSERVATIONS AND THEIR INTERPRETATION .....••• 234 3.3 THEORETICAL STUDIES OF TRANSPORT PROCESSES ••••...•.•.•....•.. 282 3.4 SUMMARY. • • • • . . . . . • • . • . • • . . • • . . • • . • • • • • . • . • • . • . . . . . . . . . • • • . • • • 294 3.5 REFERENCES. . . . . . • . . • • . . . . • . • . • . • • • • . . • . . . • • • • . • • . • . . • • • . • • • . • 296 vi TABLE OF CONTENTS CHAPTER 4: CHROMOSPHERIC EXPLOSIONS ............................... 303 4.1 INTRODUCTION. . • • • . . • • . • • • . . • . • • • • . . • • . . . • . . • . • • . • . • . • • • . . • . . • 307 4.2 CRYSTAL SPECTROMETER EXPERIMENTS ............................. 312 4.3 DEBATE OF ISSUE 1 ............................................ 313 4.4 DEBATE OF ISSUE 2............................................ 342 4.5 DEBATE OF ISSUE 3............................................ 359 4.6 REFERENCES................................................... 373 CHAPTER 5: FLARE ENERGETICS ....................................... 377 5.1 INTRODUC TION. . • • • . • . . • . • . • • . . • . . • • • . . • • • . • . . • • • • • . . . . . • • . . . . • 384 5.2 ENERGETICS OF THE IMPULSIVE PHASE ............................ 391 5.3 THE ENERGETICS OF THE GRADUAL PHASE .......................... 413 5.4 RELATIONSHIPS AMONG THE PHASES ............................... 442 5.5 CHARACTERIZATION OF TOTAL FLARE ENERGy ....................... 445 5.6 CONCLUSIONS. . • . . • . . . . . • • • • • • . . • . • . . • • . • . . . • . . • . . • . . . . . . . • . . • . 451 5A. FLARES CHOSEN FOR THE ENERGETICS STUDy ....................... 455 5B. A REVIEW OF IMPULSIVE PHASE PHENOMENA ..•.•................... 473 5.7 ACKNOWLEDGEMENTS. . . • . . . . • . . . • . . . • • . • . . . • . . . . . . • . . . . . . • . . • . . •• 486 5.8 REFERENCES. . . • • . . . • . . • . . . • . . • . • . • • • . • • . . • • . . • . . • . • • . . • . . . . . . . 486 CHAPTER 6: CORONAL MASS EJECTIONSAND CORONAL STRUCTURES ...•..•.•. 493 6.1 INTRDOCUTION. . . . • . . • . . • . . . • • . . . • . . . • • . • . . . • . . . . . . . . . • • . • . . . • • 497 6.2 OBSERVATIONS................................................. 498 6.3 THE INITIATION OF CORONAL MASS EJECTIONS •••••.•••••••.••.•.. 531 6.4 MODELLING OF CORONAL MASS EJECTIONS AND POST-FLARE ARCHES ...• 543 TABLE OF CONTENTS vii 6.5 INTERPLANETARY EFFECTS OF CORONAL MASS EJECTIONS ••.•.••••••.• 569 6.6 THE SLOWLY VARYING CORONA NEAR SOLAR ACTIVITY MAXIMUM •••••••• 574 6.7 SUMMARY. • • • • • . . • . • . • • • • • • . . . . . . . . • . • . • . • . . . • . • . • . . • . . . . . . . • • • 586 6.8 ACKNOWLEDGEMENTS. . • • . • • • • . . . • • • . • • . . . • • . • . • . . • • • • • . • . . . . . . . . • 590 6.9 REF ERENCES. . . • . . • • • • • • • . . • . . . . . • • • • • . • • . • • • . • • • . • . . • . . . • • • • • • 591 CHAPTER 7: INTERCOMPARISON OF NUMERICAL MODELS OF FLARING CORONAL LOOPS.......................................... 597 7.1 INTRODUCTION. . . . • • • • • . . • . . • • . . • • • . • • . • • • . . • • . • • • • • . . • • . . • • . • • 601 7.2 THE ORIGINAL BENCHMARK PROBLEM ....•...••.•...•••.•.•••..•••• 602 7.3 INITIAL SOLUTION COMPARISONS .....•..•.•.•••.•..••.••.••.••.•• 605 7.4 FINAL BENCHMARK PROBLEM AND SOLUTION COMPARISON .•.•...•.....• 608 7.5 CONCLUSIONS. . . . . . • . . • . . • • . . • • . . . • . . • • • • • • • . . • . . • . . • • . • • . . • • . . 610 7.6 REFERENCES. • • . • . • . . . • • . . . • . . . . . • • • . . . . . • . • . • • • . • • • • • • . . . . • . . • 612 SUBJECT INDEX ••••••••••••••••••••••••••••••.••••.••..••••..••.••••• 613 SMM PARTICIPANTS................................................... 627 FOREWORD This publication is a result of three meetings, each 5 days long, held at the Goddard Space Flight Center on January 24-28, 1983, June 8-14, 1983, and February 13-17, 1984. The meetings were held in the interim between the full operations of the Solar Maximum Mission (SMM) in 1980, and the renewed operations after its repair in orbit in April 1984. Their general objectives were as follows: o Synthesize flare studies after three years of SMM data analysis. Many analyses of individual flares and individual phenomena, often jointly across many data sources had been published, but a need existed for a broader synthesis and updating of our understanding of solar flares since the Skylab Flare Workshops held several years earlier. o Encourage a broader participation in the SMM data anlysis and combine this more fully with theory and other data sources--data obtained with other spacecraft such as the HINOTORI, P78-1, and ISEE-3 spacecrafts, and with the Very Large Array (VLA) and many other ground-based instruments. Many coordinated data sets, unprecedented in their breadth of coverage and multiplicity of sources, had been obtained within the structure of the Solar Maximum Year (SMY). o Stimulate joint studies, and publication in the general scientific literature. The intended primary benefit was for informal collaborations to be started or broadened at the Workshops with subsequent publications. o Provide a special publication resulting from this Workshop. o Provide a starting point of understanding for planning renewed full observations with the repaired SMM. The widespread interest in the Workshop topics drew over 150 people from 17 countries, which enabled the desired broad participation of people, data sources and ideas to be achieved. It also led to fragmentation of closely related subjects into topic groups in order to allow reasonably sized groups for discussion, and to allow more time for detailed discussion of each topic. The results of the studies of each group form the chapters of this book. Table 1 shows the seven topics, the topic leaders, and the sub-topics expressing the scope of each topic, shown as a set of questions. The Workshop participants, are shown at the back of the book. Some integration of topics occurred by having joint meetings between topic groups and plenary sessions. This volume is the product of research carried out by all the workshop participants, and in particular of the dedicated efforts of all x FOREWORD the team leaders. We express our sincere thanks to Drs. E. J. Schmahl, S. M. White and N. Gopalswamy for their generous help in various aspects of the production of this volume; to Ms. Gloria Wharen of GSFC and Ms. Betty J. Stevenson of U. MD. for the preparation of the manuscript; to Dr. David Bohlin of NASA for providing financial support for the workshops; to Goddard Space Flight Center, and the University of Maryland for various administrative support services. M. R. Kundu B. Woodgate Table SMM Workshop Topic Groups Chapter Topic Sub Topics Preflare Activity What changes in physical conditions can lead to instabilities? What are typical pre-flare phenomena: Leaders: E. Priest Photosphere: Velocity and magnetic shears? and V. Gaizauskas Emerging flux? Chromosphere. T.R.: UV fluctuations, down flows? UV upflows? Filament eruptions? Corona: Soft X-ray increases-mechanism? Early radio events-arch destabilizers? 2 Impulsive Phase What instabilities will occur first in plausible physical situations? Acceleration of Particles Where is the primary energy release located? What are the physical conditions in the loop implied by gamma Leader: L. Vlahos ray lines and continuum? What are accelerating mechanisms of the electrons and ions that are allowed by the observations? 3 Impulsive Phase Are hard X -ray and UV bursts the result of electron beams or Transport Processes conduction fronts') What observational constraints exist on impulsive phase models? Leader: R. Canfield What is the distribution of thermal and non-thermal plasma? 4 Chromospheric Explosions What are the observed motions during and after the impulsive I I phase" Leader: G. Doschek What is the evidence for a high pressure region at this time? I How do thermal and mechanical energies compare, e,g" using soft X -ray intensities and line shifts? Can the total energy be contained? 5 Flare Energetics Is the maximum energy in the thermal phase greater than the energy input by the impulsive phase? Leader: S-T, Wu Is there theoretical need or observational evidence for post- impulsive energy input? Is there a time inconsistency between the end of the impulsive phase and the maximum of the thermal phase? 6 Coronal Mass Ejections What is the relationship between coronal mass ejections and and Coronal Structures flares and filament eruptions? How can metric radio phenomena be integrated with other pre- Leader: E, Hildner flare, flare and post-flare phenomena and observed coronal structure? What is the detailed structure of coronal mass ejections in the corona and how do they appear in the interplanetary medium? How are they initiated and related to other solar phenomena? How well do models and observations of coronal transients compare? How did the global corona evolve in the post- maximum epoch of SMM~ 7 Numerical Analysis Do the results of different flare modelling codes agree when applied to the same initial conditions? Leader: R, Kopp