Sunspots: Theory and Observations

421 Pages·1992·8.788 MB·English

by  John H. Thomas, Nigel O. Weiss (auth.), John H. Thomas, Nigel O. Weiss (eds.)

Sunspots: Theory and Observations
NATO ASI Series
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Series C: Mathematical and Physical Sciences -Vol. 375
Sunspots:
Theory and Observations
edited Ьу
John Thomas
Н.
Department of Mechanical Engineering,
Department of Physics and Astronomy
and С.Е.К. Mees Observatory,
University of Rochester,
Rochester, NY, U.S.A.
and
Nigel Weiss
О.
Department 01 Applied Mathematics and Theoretical Physics,
University of Cambridge,
Cambridge, U.K.
Sргiпgег-Sсiепсе+Вusiпеss Media, B.V.
Proceedings о. the NATO Advanced Research Workshop оп
Тhe Тheory of Sunspots
Cambridge, u.к.
September 22-27, 1991
Ubrary of Congress Саtalogiпg-iп-PubIiсаtiоп Data
NATO Advanced Research Horkshop оп the Theory of Sunspots (1991
C• • brldge. England)
Sunspots theory and observatlons I edlted Ьу John Н. Tho.as .nd
Nlgel О. Helss.
р. с •• -- (NATO ASI serles. Serles С. M.the.atlcal and
physlc.l sclences ; vol. Э75)
"Proceedlngs of the NATO Advanced Rese.rch Horkshop оп the Theory
of Sunspots. C• • brldge. England. 22-27 Septe8ber 1991."
"Publlshed 1п cooper.tlon .lth NATO Sclentlflc Affalrs Dlvlslon."
Includes bIbl1ograph1c81 references .nd Inde ••
ISВN 978-94-010-5229-0 ISВN 978-94-011-2769-1 (eВook)
DOI 10.1007/978-94-011-2769-1
1. Sunspots--Congresses. 1. Tho8as. John Н •• 1941-
11. Helss. N. О. (Nlgel Oscar) 111. North Atlantlc T~eaty
Org.nlzatlon. Sclentlflc Affalrs Dlvls1on. IV. Tltle. V. Serles,
NATO ASI serles. Serles С. Mathe.atlc.l and physlcal sclences ; по.
Э75.
QВ525.NЭ8 1991
52Э.7'4--dс20 92-20041
ISBN 978-94-010-5229-0
Printed оп acid-free рарег
AII Rights Reserved
© 1992 Spгingeг Science+Business Media Dordгecht
Originally pubIished Ьу Kluweг Academic PubIishers in 1992
Softcoveг гepгint of the haгdcoveг 1s t edition 1992
No part of the material protected Ьу this copyгight notice тау ье reproduced ог
utilized in апу form or Ьу апу means, electronic ог mechanical, including photo
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TABLE OF CONTENTS
Preface vii
List of participants ix
I. Introduction 1
The Theory of Sunspots 3
J.H. Thomas and N.O. Weiss
II. Setting the Scene 61
Starspots 63
P.B. Byrne
The Evolution of Sunspots 75
C. Zwaan
III. Overall Structure of Sunspots 101
Continuum observations and empirical models of the thermal structure of sunspots 103
P. Maltby
Observations of the mesoscale magnetic structure of sunspots 121
A. Skumanich
Magnetohydrostatic equilibrium in sunspot models 139
K. Jahn
The fate of the heat flux blocked by sunspots 163
H.C. Spruit
IV. Fine Structure of Sunspots 173
Fine structure of umbrae and penumbrae 175
R. Muller
High resolution observations of the magnetic and velocity field of simple sunspots 195
A.M. Title, Z.A. Fronk, R.A. Shine, T.n. Tarbell, K.P. Topka,
G.B. Scharmer and TV. Schmidt
vi
Magnetoconvection 221
M.R.E. Proctor
The cluster model of sunspots 243
A.R. Choudhuri
V. Waves and Oscillations in Sunspots 259
Sunspot oscillations: observations and implications 261
B. W. Lites
Magnetohydrodynamic waves in structured magnetic fields 303
B. Roberts
Theory of umbral oscillations and penumbral waves 333
S.M. Chitre
Sunspot seismology: the interaction of a sunspot with solar p-modes 345
T.J. Bogdan
VI. The Relation of Sunspots to the Global Solar Magnetic Field 369
The formation of flux tubes at the base of the convection zone 371
D.W. Hughes
The motion of magnetic flux tubes in the convection zone and the subsurface
origin of active regions 385
F. Moreno-Insertis
VII. Concluding Summary 411
The sunspot phenomenon: a commentary 413
E.N. Parker
Index 425
PREFACE
This volume contains the invited papers presented at the NATO Advanced Research
Workshop on the Theory of Sunspots, held in Cambridge, England, 22-27 September 1991.
The idea of holding this Workshop first arose during the Solar Optical Telescope work
shop on Theoretical Problems in High-Resolution Solar Physics in Munich in 1985. At
that meeting, separate discussion groups were formed to consider specific topics in solar
physics. The discussion group on sunspots recommended that there be a meeting devoted
to theoretical problems associated with sunspots, the motivation being the consensus that
theory seemed to lag behind the observational evidence in our quest for a satisfactory un
derstanding of the physics of sunspots. This recommendation was warmly received and the
two of us were designated to organize the Workshop.
Although the Workshop eventually took place later than originally envisioned, the de
lay turned out to be fortunate and the timing of the Workshop was ideal for a number
of reasons. There have been remarkable improvements in high-resolution observations of
sunspots in the past few years, and many important new observational results were pre
sented for the first time at this Workshop (by groups working at the Lockheed Palo Alto
Research Laboratories, the Swedish and German telescopes in the Canary Islands, and
the V.S. National Solar Observatory). Vector magnetographs and Stokes polarimetry have
at last given us reliable measurements of the vector magnetic fields in sunspots. Recent
discoveries, such as the absorption of solar p-modes by sunspots, pose new and important
theoretical problems. Impressive advances in numerical simulations of processes such as
compressible magneto convection allow us to construct more realistic theoretical models of
a sunspot. Also, coincidentally, this Workshop took place exactly ten years after the last
meeting devoted exclusively to sunspots, the workshop on the Physics of Sunspots held
at Sacramento Peak Observatory in 1981 (which was itself preceded by a meeting held in
Florence in 1964).
The response to invitations to the Workshop was very positive. The vast majority of
theoreticians working on the physics of sunspots attended the Workshop, along with many
of the best observers. In all, there were 56 participants.
The program for the Workshop was planned carefully in consultation with the Scientific
Organizing Committee. After the introductory talks, the topics of specific interest divided
naturally into four scientific sessions, each under the control of a session chairman. The ti
tles of these four sessions and their respective chairmen were: Overall Structure of Sunspots
(D. J. Galloway); Fine Structure of Sunspots (H. V. Schmidt); Waves and Oscillations in
Sunspots (D. O. Gough); and The Relation of Sunspots to the Global Solar Magnetic Field
(R. Rosner). This volume contains sections corresponding to these four session topics, fol
lowed by E. N. Parker's stimulating summary. In addition, we as editors have written an
extensive introductory chapter to provide an overall perspective of the subject and make
this book more accessible to the nonspecialist.
The expressed purposes of the Workshop were to establish what is known observationally
and theoretically about sunspots, to formulate the key theoretical problems, and to identify
the most promising approaches to their solution. While we generally maintained this
vii
viii
emphasis on theory throughout the Workshop, the many important new observational
results presented at the Workshop in themselves constitute a major contribution. To reflect
this, we have decided to use the title Sunspots: Theory and Observations for these published
proceedings.
We are grateful to the members of the Scientific and Local Organizing Committees
(listed below) and the session chairmen for their important contributions to the success
of the Workshop. We thank the Department of Applied Mathematics and Theoretical
Physics, University of Cambridge, for providing the meeting room and other facilities at no
cost and Keith Moffatt for welcoming participants to the Department. We also thank Clare
College, Cambridge, where all ofthe participants were comfortably housed and well fed. We
are grateful to the Royal Astronomical Society for a grant from the Victor Na darov Fund
which enabled us to support some participants from non-NATO countries. We thank Karen
Stringer and John Turner for their help with administrative matters. We are especially
grateful to Louise Hindle for her secretarial assistance before and during the workshop and
in the preparation of this book.
Finally, on behalf of all the participants, we wish to express our gratitude to the NATO
Scientific Affairs Division for their generous financial support of this workshop.
JHT and NOW
Cambridge, January 1992
Scientific Organizing Com mittee
P. Maltby (Norway) University of Oslo
F. Moreno-Insertis (Spain) Instituto de Astrofisica de Canarias
R. Muller (France) Observatoire du Pic du Midi
E. N. Parker (USA) University of Chicago
H. U. Schmidt (Germany) Max-Planck-Institut fiir Astrophysik
J. H. Thomas (Director) (USA) University of Rochester
N. O. Weiss (Director) (UK) University of Cambridge
C. Zwaan (Netherlands) Rijksuniversiteit te Utrecht
Local Organizing Committee
D. P. Brownjohn
D. J. Galloway
D. W. Hughes
P. C. Matthews
M. R. E. Proctor
N. O. Weiss (Chairman)
LIST OF PARTICIPANTS
Aballe Villero, M.A. (Spain) Instituto de Astrofisica de Canarias, Tenerife
Bogdan, T. (USA) High Altitude Observatory, Boulder
Brownjohn, D.P. (UK) University of Cambridge
Bumba, V. ( Czechoslov. ) Ondrejov Observatory
Bunte, M. (Switzerland) ETH, Zurich
Byrne, P.B. (UK) Armagh Observatory
Chitre, S.M. (India) Tata Institute, Bombay
Choudhuri, A. Rai (India) Indian Institute of Science, Bangalore
Cram, L.E. (Australia) University of Sydney
Degenhardt, D. (Germany) University of Gottingen
Dialetis, D. (Greece) National Observatory, Athens
Evans, D.J. (UK) Queen Mary & Westfield College, London
Fox, P.A. (USA) Yale University
Frank, Z.A. (USA) Lockheed Palo Alto Research Laboratories
Galloway, D.J. (Australia) University of Sydney
Golub, L. (USA) Center for Astrophysics, Cambridge, MA
Gough, D.O. (UK) University of Cambridge
Hasan, S.S. (USA) Center for Astrophysics, Cambridge, MA
Hughes, D.W. (UK) University of Leeds
Isaak, G.R. (UK) University of Birmingham
Jahn, K. (Poland) Warsaw University Observatory
Lawrence, J.K. (USA) California State University, Northridge
Lites, B.W. (USA) High Altitude Observatory, Boulder
Livingston, W.C. (USA) National Solar Observatory, Tucson
Low, B.C. (USA) High Altitude Observatory, Boulder
Maltby, P. (Norway) University of Oslo
Matthews, P.C. (UK) University of Cambridge
Montesinos, B. (UK) University of Oxford
Moreno-Insertis, F. (Spain) Instituto de Astrofisica de Canarias, Tenerife
Muller, R. (France) Observatoire du Pic du Midi
Parker, E.N. (USA) University of Chicago
Pizzo, V.J. (USA) High Altitude Observatory, Boulder
Proctor, M.R.E. (UK) University of Cambridge
Roberts, B. (UK) University of St Andrews
Rosenthal, C.S. (USA) University of Colorado
Rosner, R. (USA) University of Chicago
Ryutova, M.P. (USSR) Institute of Nuclear Physics, Novosibirsk
Scharmer, G.B. (Sweden) Swedish Solar Observatory, La Palma
Schatten, K. (USA) NASA Goddard SFC, Greenbelt
Schmidt, H.U. (Germany) Max-Planck-Institut fUr Astrophysik, Munich
ix
x
Schmidt, W. (Germany) Kiepenheuer Institut fUr Sonnenphysik
Shine, R.A. (USA) Lockheed Palo Alto Research Laboratories
Similon, P.L. (USA) Yale University
Skumanich, A. (USA) High Altitude Observatory, Boulder
Solanki, S.K. (Switzerland) ETH, Zurich
Spruit, H.C. (Germany) Max-Planck-Institut fUr Astrophysik, Munich
Staude, J. (Germany) Zentralinstitut fiir Astrophysik, Potsdam
Strous, L.H. (Netherlands) Rijksuniversiteit te Utrecht
Theobald, M.L. (USA) Yale University
Thomas, J .H. (USA) University of Rochester
Title, A.M. (USA) Lockheed Palo Alto Research Laboratories
Watson, P.G. (UK) University of Cambridge
Weiss, N.O. (UK) University of Cambridge
Wilson, P.R. (Australia) University of Sydney
Zhugzhda, Yu.D. (USSR) IZMIRAN, Troitsk
Zwaan, C. (Netherlands) Rijksuniversiteit te Utrecht