J. Space Weather Space Clim. 3 (2013) A18 DOI: 10.1051/swsc/2013039 Ó F. Zuccarello et al., Published by EDP Sciences 2013 RESEARCH ARTICLE OPEN ACCESS Solar activity and its evolution across the corona: recent advances Francesca Zuccarello1,*, Laura Balmaceda2, Gael Cessateur3, Hebe Cremades4, Salvatore L. Guglielmino5, Jean Lilensten6, Thierry Dudok de Wit7, Matthieu Kretzschmar7, Fernando M. Lopez2, Marilena Mierla8,9,10, Susanna Parenti8, Jens Pomoell11, Paolo Romano5, Luciano Rodriguez8, Nandita Srivastava12, Rami Vainio11, Matt West8, and Francesco P. Zuccarello13 1 Dipartimento di Fisica e Astronomia, Sez. Astrofisica, Universita` di Catania, Via S. Sofia 78, 95123 Catania, Italy *Corresponding author: [email protected] 2 Instituto de Ciencias Astrono´micas, de la Tierra y el Espacio, ICATE-CONICET, Av. Espan˜a Sur 1512, J5402DSP, San Juan, Argentina 3 Physical-Meteorological Observatory/World Radiation Center, Davos, Switzerland 4 Universidad Tecnolo´gica Nacional – Facultad Regional Mendoza/CONICET, Rodrı´guez 273, M5502AJE, Mendoza, Argentina 5 INAF – Osservatorio Astrofisico di Catania, Via S. Sofia 78, 95123, Catania, Italy 6 UJF-Grenoble 1/CNRS-INSU, Institut de Plane´tologie et d’Astrophysique de Grenoble (IPAG) UMR 5274, 38041 Grenoble, France 7 LPC2E/CNRS (UMR 7328) and University of Orle´ans, 3A avenue de la Recherche Scientifique, 45071 Orle´ans Cedex 2, France 8 Solar – Terrestrial Center of Excellence – SIDC, Royal Observatory of Belgium, Av. Circulaire 3, 1180 Brussels, Belgium 9 Institute of Geodynamics of the Romanian Academy, Jean-Louis Calderon 19–21, Bucharest-37 020032, Romania 10 Research Center for Atomic Physics and Astrophysics, Faculty of Physics, University of Bucharest, Str. Atomistilor 405, 077125 Magurele-Ilfov, Romania 11 Department of Physics, POB 64, 00014 University of Helsinki, Finland 12 Udaipur Solar Observatory, Physical Research laboratory, Udaipur 313001, India 13 Centre for mathematical Plasma Astrophysics, KU Leuven, Celestijnenlaan 200B, 3001 Leuven, Belgium Received 16 June 2012 / Accepted 22 March 2013 ABSTRACT Solar magnetism is responsible for the several active phenomena that occur in the solar atmosphere. The consequences of these phenomena on the solar-terrestrial environment and on Space Weather are nowadays clearly recognized, even if not yet fully under- stood. In order to shed light on the mechanisms that are at the basis of the Space Weather, it is necessary to investigate the sequence of phenomena starting in the solar atmosphere and developing across the outer layers of the Sun and along the path from the Sun to the Earth. This goal can be reached by a combined multi-disciplinary, multi-instrument, multi-wavelength study of these phenom- ena, starting with the very first manifestation of solar active region formation and evolution, followed by explosive phenomena (i.e., flares, erupting prominences, coronal mass ejections), and ending with the interaction of plasma magnetized clouds expelled from the Sun with the interplanetary magnetic field and medium. This wide field of research constitutes one of the main aims of COST Action ES0803: Developing Space Weather products and services in Europe. In particular, one of the tasks of this COST Action was to investigate the Progress in Scientific Understanding of Space Weather. In this paper we review the state of the art of our comprehension of some phenomena that, in the scenario outlined above, might have a role on Space Weather, focusing on the researches, thematic reviews, and main results obtained during the COST Action ES0803. Key words. solar activity – active regions – coronal mass ejections – shock propagation – solar irradiance 1. Introduction of Space Weather: recent advances on solar dynamics (the origin of Space Weather), space plasma processes COST Action ES0803: Developing Space Weather products (the transmission process) and long-term variability of and services in Europe had the main objective of fostering col- the Sun, interplanetary space and Geospace (the med- laboration between European Space Weather researchers, data ium which moderates it) will be compiled and ana- providers, and service operators aiming at the assessment of lyzed for a successful description, nowcasting and the existing potential in operational Space Weather infrastruc- eventually forecasting of the state of the space tures and models, services, and collaborative research. The environment’’. Memorandum of Understanding of this COST Action states that: ‘‘Space Weather originates mainly in solar activity and The Scientific Work-plan, Methods, and Means of the affects the interplanetary space and planetary magnetospheres, COST Action foresaw the Identification of scientific under- ionospheres, and atmospheres’’. standing of physical processes which lead to various Space One of the main research tasks coordinated by this COST Weather phenomena. In particular, the authors of this paper Action concerns the: were involved in the Task Sources of solar activity,which ‘‘Detailed identification of forefront scientific research was divided in some sub-tasks, among which we recall the on the physical processes responsible for various states following ones: (a) Dynamics of active regions, flares, erupting This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. J. Space Weather Space Clim. 3 (2013) A18 prominences, CMEs, magnetic helicity transport; (b) Simula- an evolution time varying from a ten of minutes to some hours. tions of solar eruptions, particle acceleration, and turbulence; The phenomena that occur during a flare produce heating of the (c) three-dimensional (3D) reconstruction of CMEs from space- chromospheric and coronal plasma and intense electric fields craft observations. that accelerate charged particles. We therefore describe here the state of the art of our knowl- Coronal mass ejections are expulsions of magnetized edge on these phenomena, focusing on the main results on the plasma from the solar corona and, from an energetic point of Sources of solar activity obtained during this COST Action, and view, they reach the same (or higher) order of magnitude of providing some illustrative examples of the researches that have the flares; they can moreover pour in the space up to several been carried out thanks to this collaboration. billion tons of coronal plasma. Such phenomena can occur In this regard, we would like to stress that the rich and com- many times a day and can accelerate the solar plasma up to À1 plex variety of phenomena observed in the solar atmosphere 3000 km s . Even if they have been extensively studied since provides precious information that helps us improve our under- their discovery, back in the 1970s of the XX century, a com- standing of the modes of interaction between a plasma and plete model for their explanation is still lacking. magnetic fields of the order of 10–103 Gauss. In particular, Large-amplitude waves in the solar corona are a direct con- the study of active regions (ARs) on the Sun supplies informa- sequence of the dynamic magnetic activity of the corona: for tion on how a plasma can be modified, in terms of temperature, instance, shock waves associated with eruptions occurring in density, velocity, etc., by the presence of magnetic fields that the corona are believed to be linked to a number of transient emerge from sub-photospheric layers as bundles of magnetic phenomena such as metric type II bursts, Moreton and extreme flux tubes, and how successively the magnetic field spreads ultraviolet (EUV) waves, and solar energetic particle (SEP) over the plasma itself. events. Eruptive phenomena, often caused by the sudden Nowadays, the different layers of the solar atmosphere are release of energy stored in the coronal magnetic field during accessible with different spatial resolution. With current instru- processes of magnetic reconnection, can produce serious effects ments it is in fact possible to achieve a spatial resolution of on the Sun-Earth environment and can trigger a series of phe- 00 00 00 nomena (auroras, magnetic storms, charged particle reaching 0_2 in photosphere and chromosphere and 1 –2 in corona. This makes it very difficult to link the different observations the ionosphere of the Earth), which are currently studied in and properly interpret them to give a global view: the fact that the context of the Space Weather (see, e.g., Messerotti et al. the phases of activation and eruption of a filament are followed 2009). In this regard, an improvement of our forecasting capa- in chromosphere and corona by different instruments, and the bilities about the effects of solar phenomena on the Space difficulty in identifying different strands and small features at Weather is essential in order to guarantee that ground- and satel- different atmospheric heights, are typical examples of this lite-based technologies work in a reliable way for a more inno- problem. vative and safer society. Within the above-mentioned limitations, during the last few In the framework of the solar activity investigation, an years the possibility of carrying on observations from both important role is played by the Total Solar Irradiance (TSI). Earth and space in various spectral ranges has provided new Understanding the variability of the TSI and of the solar spec- and important indications on the modes