Turbulence, Waves and Instabilities in the Solar Plasma

Transcription

1 Turbulence, Waves and Instabilities in the Solar Plasma

2 NATO Science Series A Series presenting the results of scientific meetings supported under the NATO Science Programme. The Series is published by IOS Press, Amsterdam, and Kluwer Academic Publishers in conjunction with the NATO Scientific Affairs Division Sub-Series I. Life and Behavioural Sciences IOS Press II. Mathematics, Physics and Chemistry Kluwer Academic Publishers III. Computer and Systems Science IOS Press IV. Earth and Environmental Sciences Kluwer Academic Publishers V. Science and Technology Policy IOS Press The NATO Science Series continues the series of books published formerly as the NATO ASI Series. The NATO Science Programme offers support for collaboration in civil science between scientists of countries of the Euro-Atlantic Partnership Council. The types of scientific meeting generally supported are Advanced Study Institutes and Advanced Research Workshops, although other types of meeting are supported from time to time. The NATO Science Series collects together the results of these meetings. The meetings are co-organized bij scientists from NATO countries and scientists from NATO s Partner countries countries of the CIS and Central and Eastern Europe. Advanced Study Institutes are high-level tutorial courses offering in-depth study of latest advances in a field. Advanced Research Workshops are expert meetings aimed at critical assessment of a field, and identification of directions for future action. As a consequence of the restructuring of the NATO Science Programme in 1999, the NATO Science Series has been re-organised and there are currently Five Sub-series as noted above. Please consult the following web sites for information on previous volumes published in the Series, as well as details of earlier Sub-series Series II: Mathematics, Physics and Chemistry Vol. 124

3 Turbulence, Waves and Instabilities in the Solar Plasma edited by R. Erdélyi University of Sheffield, Sheffield, United Kingdom K. Petrovay Eötvös University, Budapest, Hungary B. Roberts University of St. Andrews, St. Andrews, United Kingdom and M. Aschwanden Lockheed Martin Solar & Astrophysics Laboratory, Palo Alto, U.S.A. Springer-Science+Business Media, B.V.

4 Proceedings of the NATO Advanced Research Workshop on Turbulence, Waves, and Instabilities in the Solar Plasma Lillafured, Hungary September 2002 A C.I.P. Catalogue record for this book is available from the Library of Congress. ISBN DOI / ISBN (ebook) Printed on acid-free paper All Rights Reserved 2003 Springer Science+Business Media Dordrecht Originally published by Kluwer Academic Publishers in 2003 Softcover reprint of the hardcover 1st edition 2003 No part of this work may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, microfilming, recording or otherwise, without written permission from the Publisher, with the exception of any material supplied specifically for the purpose of being entered and executed on a computer system, for exclusive use by the purchaser of the work.

5 Contents PREFACE LIST OF CONTRIBUTORS vii xi PART ONE / INSTABILITIES AND MOTIONS IN THE SOLAR INTERIOR AND TACHOCLINE H. C. Spruit / A dynamo in the radiative interior 3 K. Petrovay/ Turbulence and its Sources Below the Convective Zone 23 A. Brandenburg, N. E. L. Haugen and W. Dobler/ MHD simulations of small and large scale dynamos 33 PART TWO / TURBULENCE IN THE CONVECTIVE ZONE AND PHOTOSPHERE A. Kosovichev/ Helioseismic observations of plasma motions in the solar convection zone 57 L. L. Kitchatinov/ Turbulent Transport in Rotating and Magnetized Fluids 81 PART THREE / PARKER INSTABILITY AND FLUX TUBE DYNAMICS T. Magara/ Three-dimensional Evolution of a Magnetic Flux Tube Emerging into the Solar Atmosphere 99 O. Steiner/ Photospheric magnetic field at small scales 117 PART FOUR / WAVES AND OSCILLATIONS IN THE SOLAR ATMOSPHERE R. J. Rutten/ Waves in the chromosphere: observations 145

6 vi B. Roberts and V. M. Nakariakov/ Theory of MHD Waves in the Solar Corona 167 J. L. Ballester/ Prominence Oscillations: Theory 193 M. J. Aschwanden/ Review of Coronal Oscillations - An Observer s View 215 M. S. Ruderman/ Nonlinear Waves in the Magnetically Structured Solar Atmosphere 239 PART FIVE / TURBULENCE AND RECONNECTION IN THE SOLAR CORONA B. De Pontieu/ TRACE and Ground-based Observations of Small-scale Dynamics in Active Regions 277 L. van Driel-Gesztelyi/ Observational Signatures of Magnetic Reconnection 297 M. Ryutova and R. Shine/ Self-organized Structures in the Solar Atmosphere: Theory and Observations. 323 PART SIX / SOLAR WIND L. Ofman/ Wave Heating and Acceleration of the Fast Solar Wind 349 G. Erdős/ Waves and turbulence in the solar wind 367 Index 387

7 Preface This volume contains the outlook reviews presented at the NATO Workshop Turbulence, Waves, and Instabilities in the Solar Plasma, held September 2002 in Budapest, Hungary. Further contributions to the meeting (focus reviews, contributed talks and posters) are being published in the companion volume Contributions on Turbulence, Waves, and Instabilities in the Solar Plasma in the series Publications of the Department of Astronomy of Eötvös University, no. 13. In recent years, significant advances have been made in both theoretical and observational studies of small-scale motions such as waves and turbulence, and of the instabilities giving rise to them, in different layers of the Sun. Owing to the notable extensive and intensive development in the field of solar physics, specialization has reached a degree where interaction between workers studying e.g. the solar interior and solar flares has become scarce. The purpose of our NATO workshop was to facilitate interchange and communication between diverse groups studying different layers and regions of the Sun but from the same aspect, concentrating on the study of small-scale motions. While the main emphasis was on the common theoretical roots of these phenomena, observational aspects were also treated extensively. For the outlook reviews contained in these proceedings the Editors invited papers by speakers of a wide range of solar physics but focusing on the study of small-scale motions. Since the field is enormous we had to make a somewhat arbitrary selection of topics, hoping to cover all key aspects. Among the fields of particular interest, where especially intriguing developments took place in recent years, one should mention the study of the solar tachocline (Chapters 1 to 3). The tachocline is a thin layer in the solar interior, below the convective zone, where the differential rotation characterizing the outer layers suddenly disappears, while the radiative zone below is rotating rigidly. The very existence of this layer has only been known for about a decade, and it has been realized that it plays a crucial role in the solar dynamo, and probably also in diffusive processes below the convective zone. The physics of the tachocline is presently a very vii

8 viii active research area, and, owing to the complex processes taking place there simultaneously (overshooting convection, shearing and rotational instabilities, turbulent diffusion and other turbulent transport processes, magnetic fields) important new physics can be learnt from its study. Another exciting and strongly related field of interest is the heating process that generates and sustains the observed hot solar atmosphere (in particular the corona) which has so far defied a quantitative understanding despite the multitude of efforts spanning over half a century (Chapters 4 and 5). This workshop addressed these questions by investigating small-scale heating blocks with theoretical and observational tools. Solar atmospheric heating blocks have recently been detected with unprecedented sensitivity (SOHO, TRACE). There is, however, an active debate about the importance of these events for the heating of the solar atmosphere (corona). Studying the power spectrum of small-scale dynamical events is crucial to determine the degree of the turbulent nature of the solar atmospheric heating. Further on, the role of MHD waves generating this turbulence (or vice-versa!) was addressed and has not been carried out extensively before. The selection of invited speakers from a wide range of countries, both from Eastern and Western Europe and America, concentrated on the researchers currently most active in the field, mostly on a postdoctoral/tenure/fresh faculty position level. A number of senior experts and PhD students were also invited. Scientists from NATO partner countries were especially encouraged to apply and we had a maximum turn-out of altogether 50 scientists! The relative isolation of the venue (Hotel Normafa, Budapest), as well as the fact that the participants all stayed at the same place, where the conference was also held, contributed to the success of the meeting, offering plenty of opportunities to meet and exchange ideas. The excursion to Szentendre (St. Andrews in English) followed by the conference dinner in a rustic Hungarian restaurant, and the visit to the famous Opera shall remain a unique experience. During the workshop we organised three panel discussions which proved to be especially successful. Two of these concerned the two most disputed problems mentioned above, i.e. the solar dynamo tachocline problem and the issue of coronal heating. The closing discussion offered an opportunity to raise questions concerning all topics discussed during the meeting. The workshop was sponsored by NATO s ARW program (ref. no. PST. ARW ) for which we are grateful. We also would like to express

9 our gratitude to the staff of the Dept. of Astronomy, Eötvös University Budapest for their contribution to have a smooth and effective workshop. Substantial assistance by Ms E. Forgács-Dajka in the preparation of manuscripts of the proceedings is very much appreciated. Robertus Erdélyi Sheffield, England (UK) 27 January 2003 ix

10 List of Contributors Name Address Aschwanden, M. J. Ballester, J. L. Brandenburg, A. De Pontieu, B. Erdélyi, R. Erdős, G. Lockheed-Martin Solar and Astrophysics Lab Hanover St., O/L9-41, Bldg. 252, Palo Alto, CA 94304, USA Departament de Física Universitat de les Illes Balears E Palma de Mallorca, Spain Nordita Blegdamsvej 17 DK-2100 Copenhagen Ø, Denmark Lockheed-Martin Solar and Astrophysics Lab Hanover St., O/L9-41, Bldg. 252, Palo Alto, CA 94304, USA Space & Atmosphere Research Center Department of Applied Mathematics University of Sheffield Hicks Building, Hounsfield Road Sheffield, S3 7RH, England (UK) KFKI Research Institute for Particle and Nuclear Physics Budapest, Hungary xi

11 xii Kitchatinov, L. L. Kosovichev, A. Magara, T. Ofman, L. Petrovay, K. Roberts, B. Ruderman, M. S. Rutten, R. J. Institute for Solar-Terrestrial Physics P.O.Box 4026 Irkutsk, , Russian Federation Stanford University Stanford, CA Department of Physics Montana State University POB , Bozeman, MT 59717, USA NASA Goddard Space Flight Center Code 682 Greenbelt MD 20771, USA Eötvös University, Department of Astronomy Budapest, Pf. 32 H-1518 Hungary School of Mathematics and Statistics University of St Andrews St Andrews, Fife, KY16 9SS, Scotland, UK Department of Applied Mathematics University of Sheffield Hicks Building, Hounsfield Road Sheffield, S3 7RH, UK Sterrekundig Instituut Postbus NL-3508 TA Utrecht, The Netherlands

12 xiii Ryutova, M. Spruit, H. C. Steiner, O. van Driel-Gesztelyi, L. Lawrence Livermore National Laboratory Institute of Geophysics and Planetary Physics Livermore, CA 94550, USA Max-Planck-Institut für Astrophysik Postfach Garching, Germany Kiepenheuer-Institut für Sonnenphysik, Schöneckstrasse 6 D Freiburg, Germany steiner@kis.uni-freiburg.de Centre for Plasma Astrophysics K.U. Leuven, Celestijnenlaan 200B, 3001 Leuven, Belgium Lidia.vanDriel@obspm.fr