Astrophysics and Space Science Proceedings Volume 30 For further volumes: http://www.springer.com/series/7395 • The Sun: New Challenges Proceedings of Symposium 3 of JENAM 2011 Editors Vladimir N. Obridko Katya Georgieva Yury A. Nagovitsyn 123 Editors Vladimir N. Obridko Katya Georgieva IZMIRAN SSTRI-BAS Troitsk Moscow region Institute - KMI Russia Sofia Bulgaria Yury A. Nagovitsyn Pulkovo Observatory Saint Petersburg Russia ISSN 1570-6591 ISSN 1570-6605 (electronic) ISBN 978-3-642-29416-7 ISBN 978-3-642-29417-4 (eBook) DOI 10.1007/978-3-642-29417-4 Springer Heidelberg New York Dordrecht London Library of Congress Control Number: 2012943601 c Springer-Verlag Berlin Heidelberg 2012 This work is subject to copyright. 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Violations are liable to prosecution under the respective Copyright Law. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. While the advice and information in this book are believed to be true and accurate at the date of publication, neither the authors nor the editors nor the publisher can accept any legal responsibility for any errors or omissions that may be made. The publisher makes no warranty, express or implied, with respect to the material contained herein. Printed on acid-free paper Springer is part of Springer Science+Business Media (www.springer.com) Preface This book contains the Proceedings of the Joint European and National Astronomi- cal Meeting (JENAM-2011) held on July 4–8, 2011 at St. Petersburg. The main topics discussed at the meeting were: 1. The unusual sunspot minimum—challenge to the solar dynamo theory 2. New observational window: terra-Hertz emission 3. Wavy corona 4. Space weather agents—initiation, propagation, and forecast. Now and again, the Sun sets new problems before the astronomers. One of such problems is the abnormal behavior of solar activity during the past, 23rd cycle. Even now, it is not clear whether the anomalies have ceased with the beginning of the new cycle 24 or we are still facing a long period of low solar activity. The anomalies in question have manifested themselves in various parameters, such as the sunspots per se, the number and intensity of coronal mass ejections, extraordinary brightness distributions in the corona, solar wind parameters, and the persistent big low latitude coronal holes. We discussed at the symposium the following problems: • What are the characteristics of solar activity that display abnormal behavior? Is it possible that we are on the threshold of a strong decrease of solar activity? Were analogous episodes in the history of solar activity? What are the similar features and differences between the activity cycles in the Sun and stars? • Are the present-day theories able to account for strong variations in the height of the cycles (up to an order of magnitude) on one and the same star? Is it possible to predict the heights and peculiarities of the cycles on the basis of the dynamo theory? • Are there additional arguments for the influence of planets on solar activity? Observations in the sub-THz range of large solar flares have revealed a mys- terious spectral component increasing with frequency and hence distinct from the microwave component commonly accepted to be produced by gyrosynchrotron v vi Preface (GS) emission from accelerated electrons. Evidently, having a distinct sub-THz component requires either a distinct emission mechanism (compared to the GS one) or different properties of electrons and location or both. It is interesting to discuss the complete list of possible emission mechanisms. It is the magnetic field that determines the variations of the coronal brightness. However, the mechanism of the corona heating and, therefore, of the relationship between the corona brightness and magnetic field is unclear. This is, obviously, due to the fact that there are several heating mechanisms that play different roles in different areas (active regions, quiet Sun, coronal holes). So far, it is not clear whether the DC or AC mechanisms prevail in one or another object in the Sun. What is the role of different-scale magnetic fields in the heating of the solar corona and how does their relative contribution change with time? What kinds of manifold observational waves and oscillations are significant to understand the heating of upper solar atmosphere? The progress in studying the key objects of the Space Weather problem—CMEs and high-speed solar wind streams will be, apparently, achieved owing to a wide use of stereoscopic data from the STEREO-A and spacecraft as well as the high-quality solar obtained in several channels corresponding to different plasma temperatures (SDO). The main topics to discuss were as follows: • The nature of coronal mass ejections and their connection to various-scale fields • The acceleration of the solar wind and connection between the solar wind and various features in the Sun • 3D structure and physical parameters of CME sources, including the flares and filament eruptions • The correlation between coronal hole characteristics and the parameters of the solar wind. Troitsk Vladimir Obridko Saint Petersburg Yury Nagovitsyn Sofia Katya Georgieva Contents The Unusual Sunspot Minimum: Challenge to the Solar Dynamo Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 V.N. Obridko, Yu.A. Nagovitsyn, and Katya Georgieva The Evolution of Cyclic Activity of the Sun in the Context of Physical Processes on Late-Type Stars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Maria M. Katsova Long-Term Variations of the Solar Supergranulation Size According to the Observations in CaIIK Line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 A.G. Tlatov On the Problem of Heat Transport in the Solar Atmosphere . . . . . . . . . . . . . . . 39 A.V. Oreshina, O.V. Ptitsyna, and B.V. Somov Dynamics of the Electrical Currents in Coronal Magnetic Loops . . . . . . . . . . 47 V.V. Zaitsev, K.G. Kislyakova, A.T. Altyntsev, and N.S. Meshalkina Observations of Solar Flares from GHz to THz Frequencies . . . . . . . . . . . . . . . 61 Pierre Kaufmann On the Interaction of Solar Rotational Discontinuities with a Contact Discontinuity Inside the Solar Transition Region as a Source of Plasma Heating in the Solar Corona . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 S.A. Grib and E.A. Pushkar Complex Magnetic Evolution and Magnetic Helicity in the Solar Atmosphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 Alexei A. Pevtsov On Our Ability to Predict Major Solar Flares . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 Manolis K. Georgoulis vii viii Contents Chromospheric Evaporation in Solar Flares . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 Zongjun Ning Evolutionary of Discontinuous Plasma Flows in the Vicinity of Reconnecting Current Layers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117 L.S. Ledentsov and B.V. Somov Analytical Models of Generalized Syrovatskii’s Current Layer with MHD Shock Waves .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133 S.I. Bezrodnykh, V.I. Vlasov, and B.V. Somov Solar Convection and Self-Similar Atmosphere’s Structures . . . . . . . . . . . . . . . 145 A.A. Agapov, E.A. Bruevich, and I.K. Rozgacheva SDO in Pulkovo Observatory .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155 E. Benevolenskaya, S. Efremov, V. Ivanov, N. Makarenko, E. Miletsky, O. Okunev, Yu. Nagovitsyn, L. Parfinenko, A. Solov’ev, A. Stepanov, and A. Tlatov Variations of Microwave Emission and MDI Topology in the Active Region NOAA 10030 Before and During the Power Flare Series . . . 165 I.Yu. Grigoryeva, V.N. Borovik, N.G. Makarenko, I.S. Knyazeva, I.N. Myagkova, A.V. Bogomolov, D.V. Prosovetsky, and L.M. Karimova Scenario of Evolution of the Epoch of Minimum at the Final Stage of Cycle 23 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179 N.A. Lotova and V.N. Obridko Solar Magnetic Fields as a Clue for the Mystery of the Permanent Solar Wind and the Solar Corona . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189 M.A. Mogilevsky and K.I. Nikolskaya Two Types of Coronal Bright Points in the 24-th Cycle of Solar Activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197 Chori T. Sherdanov, Ekaterina P. Minenko, A.M. Tillaboev, and Isroil Sattarov The Self-Similar Shrinkage of Force-Free Magnetic Flux Ropes in a Passive Medium of Finite Conductivity . . . . . . . . . . . . . . . . . . . . . . . . . . . 203 A.A. Solov’ev Solar Activity Indices in the Cycles 21–23.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221 A.A. Borisov, E.A. Bruevich, I.K. Rozgacheva, and G.V. Yakunina Coronal Mass Ejections on the Sun and Their Relationship with Flares and Magnetic Helicity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229 G.A. Porfir’eva, G.V. Yakunina, V.N. Borovik, and I.Y. Grigoryeva The Unusual Sunspot Minimum: Challenge to the Solar Dynamo Theory V.N. Obridko, Yu.A. Nagovitsyn, and Katya Georgieva Abstract The last cycle 23 was low, long, complex, and very unusual. The “peculiarity” of the minimum was that the field was weak, but also that the morphology of the heliosphere was very complex. A large number of features of intermediate scale—neither global nor local—were observed. There are reasons to believe that the amplitude and the period of a cycle are determined by the large-scale meridional circulation which, in turn, may be modulated by planetary tidal forces. There are evidences that at present the deep meridional circulation is very slow, from which a low and late maximum of cycle 24 can be predicted. Calculations of the planetary tidal forces indicate that cycle 25 will be still lower, and therefore cycle 24 is the beginning of a secular solar activity minimum. Various prediction methods are summarized, all indicating that we are entering a period of moderately low activity, and the possibility of a Maunder-type minimum is very small. Arguments are also presented in favor of a near-surface dynamo. V.N. Obridko ( ) The Pushkov institute of terrestrial magnetism, ionosphere and radiowave propagation, Russian Academy of Science, Troitsk, 142190, Russia e-mail: 2 V.N. Obridko et al. 1 Introduction We begin with the question why the paper is headed in this way, and in what properly is the challenge to the solar dynamo theory. The last minimum and the whole cycle 23 were quite strange. Does this strangeness really go beyond the limits of the formerly observed scatter in the activity cycles’ characteristics? And can we at present even broadly identify the reasons for the significant variations in the solar cycles’ characteristics? It should be noted that the main peculiarity of the last minimum was that the fields were weak and the morphology of the heliosphere was complex. A big number of features of intermediate scale—neither global non local—were observed. Can’t this be used to assess the amplitude of the next maximum? What are the recent models of solar dynamo, and can they provide a description of the characteristics of the 11-year cycle, in particular the observed variations in the sunspot magnetic field intensity, and what the level of activity in a given cycle depends on? Finally, what can we expect of cycle 24 which we have entered? 2 Some Characteristics of the 23/24 Solar Minimum In Fig. 1 the monthly number of the spotless days in the last five solar cycles is shown based on data from the Mountain station of Pulkovo observatory [1]. It can be seen that cycle 23 which just ended is characterized by a big number of spotless days. However, during the last century, the number of spotless days was even bigger in 1913 minimum (Fig. 2). The number of sunspots in 2008 was extremely low, but the heliospheric current sheet was not flat as it should be during the minimum when all other harmonics disappear except for the axial dipole. Figure 3 demonstrates the coronal structure during three consecutive high-latitude scans of the Ulysses spacecraft. It can be seen that the situation in 2008 minimum strikingly differs from the situation in 1996 minimum. The structure of the corona in 1996 is standard, with a pronounced streamer in the equatorial plane which is an evidence of a typical axial dipole structure. In 2008, on the other hand, numerous extra-equatorial streamers are observed which cannot be associated with the axial dipole. Figure 4 demonstrates the cyclical variation of the effective multipolarity index introduced in [2]. This index is equal to 2 for a dipole and strongly increases in the cycle maximum. In the 23/23 cycle minimum the situation is significantly different from 20/21 and 21/22 minima. While in the previous minima the index dropped to almost dipole values, the decreased which began during the declining phase of cycle 23 was later replaced by an increase to almost a maximum value. The increase of this index is an indication of an unusually large number of equatorial coronal holes. The