Large Scale Structures And Their Role In Solar Activity

A collection of papers edited by four experts in the field, this book sets out to describe the way solar activity is manifested in observations of the solar interior, the photosphere, the chromosphere, the corona and the heliosphere. The 11-year solar activity cycle, more generally known as the sunspot cycle, is a fundamental property of the Sun. This phenomenon is the generation and evolution of magnetic fields in the Sun’s convection zone, the photosphere. It is only by the careful enumeration and description of the phenomena and their variations that one can clarify their interdependences. The sunspot cycle has been tracked back about four centuries, and it has been recognized that to make this data set a really useful tool in understanding how the activity cycle works and how it can be predicted, a very careful and detailed effort is needed to generate sunspot numbers. This book deals with this topic, together with several others that present related phenomena that all indicate the physical processes that take place in the Sun and its exterior environment. The reviews in the book also present the latest theoretical and modelling studies that attempt to explain the activity cycle. It remains true, as has been shown in the unexpected characteristics of the first two solar cycles in the 21st century, that predictability remains a serious challenge. Nevertheless, the highly expert and detailed reviews in this book, using the very best solar observations from both ground- and space based telescopes, provide the best possible report on what is known and what is yet to be discovered. Originally published in Space Science Reviews, Vol 186, Issues 1-4, 2014.

The SECCHI A and B instrument suites (Howard et al. , 2006) onboard the two STEREO mission spacecraft (Kaiser, 2005) are each composed of: one Extreme Ultra-Violet Imager (EUVI), two white-light coronagraphs (COR1 and COR2), and two wide-angle heliospheric imagers (HI1 and HI2). Technical descriptions of EUVI, COR1 and the HIs can be found in Wuelser et al. (2004), Thompson et al. (2003), and De?se et al. (2003), respectively. The images produced by SECCHI represent a data visualization challenge: i) the images are 2048×2048 pixels (except for the HIs, which are usually binned onboard 2×2), thus the vast majority of computer displays are not able to display them at full frame and full r- olution, and ii) more importantly, the ?ve instruments of SECCHI A and B were designed to be able to track Coronal Mass Ejections from their onset (with EUVI) to their pro- gation in the heliosphere (with the HIs), which implies that a set of SECCHI images that covers the propagation of a CME from its initiation site to the Earth is composed of im- ?1 ages with very different spatial resolutions – from 1. 7 arcsecondspixel for EUVI to 2. 15 ?1 arcminutespixel for HI2, i. e. 75 times larger. A similar situation exists with the angular scales of the physical objects, since the size of a CME varies by orders of magnitude as it expands in the heliosphere.

This set of lectures collects surveys of open problems in celestial dynamics and dynamical astronomy applied to solar, extra-solar and galactic systems. The discovery and thus the possibility to study many new extra-solar planetary systems have spurred new developments in the field and enabled the testing and enlargement of the domains of validity of theoretical predictions through the Nekhoroshev theorem.

Helioseismology has enabled us to probe the internal structure and dynamics of the Sun, including how its rotation varies in the solar interior. The unexpected discovery of an abrupt transition - the tachocline - between the differentially rotating convection zone and the uniformly rotating radiative interior has generated considerable interest and raised many fundamental issues. This volume contains invited reviews from distinguished speakers at the first meeting devoted to the tachocline, held at the Isaac Newton Institute. It provides a comprehensive account of the understanding of the properties and dynamics of the tachocline, including both observational results and major theoretical issues, involving both hydrodynamic and magnetohydrodynamic behaviour. The Solar Tachocline is a valuable reference for researchers and graduate students in astrophysics, heliospheric physics and geophysics, and the dynamics of fluids and plasmas.

In this dissertation, the structure, dynamics and evolution of two quiescent prominences were studied. Quiescent prominences are large structures and mainly associated with the quiet Sun region. For the analysis, the high spatial and temporal cadence data from the Solar Dynamic Observatory (SDO), and the Solar Terrestrial Relations Observatory (STEREO) were used. The observations from two different directions were combined and the prominence in 3D were studied. In the study of polar crown prominence, the prominence flows on limb were mainly investigated and its association with on-disk brightenings were found. The merging of diffused active region flux in the already formed chain of prominence caused the several brightenings in the filament channel and also injected the plasma upward with an average velocity of 15 km/s. In another study, the triggering mechanism of a quiescent tornado-like prominence was investigated. Flares from the neighboring active region triggered the tornado-like motions on the top of the prominence. Active region field contracts after the flare which results in the expansion of prominence cavity. The prominence helical magnetic field expands and plasma moves along the field lines which appear as a tornado-like activity. These observational investigations led to the understanding of structure and dynamics of quiescent prominences, which could be useful for theoretical prominence models.

This volume is devoted to the dynamics and diagnostics of solar magnetic fields and plasmas in the Sun’s atmosphere. Five broad areas of current research in Solar Physics are presented: (1) New techniques for incorporating radiation transfer effects into three-dimensional magnetohydrodynamic models of the solar interior and atmosphere, (2) The connection between observed radiation processes occurring during flares and the underlying flare energy release and transport mechanisms, (3) The global balance of forces and momenta that occur during flares, (4) The data-analysis and theoretical tools needed to understand and assimilate vector magnetogram observations and (5) Connecting flare and CME phenomena to the topological properties of the magnetic field in the Solar Atmosphere. The role of the Sun’s magnetic field is a major emphasis of this book, which was inspired by a workshop honoring Richard C. (Dick) Canfield. Dick has been making profound contributions to these areas of research over a long and productive scientific career. Many of the articles in this topical issue were first presented as talks during this workshop and represent substantial original work. The workshop was held 9 – 11 August 2010, at the Center Green campus of the National Center for Atmospheric Research (NCAR) in Boulder, Colorado. This volume is aimed at researchers and graduate students active in solar physics, solar-terrestrial physics and magneto-hydrodynamics. Previously published in Solar Physics journal, Vol. 277/1, 2012.

The Sun and stars rotate in di?erent ways and at di?erent velocity rates. The knowledge of how they rotate is important in understanding the formation and evolution of stars and their structure. The closest star to our Earth, the Sun, is a good laboratory to study in detail the rotation of a G star and allows to test new ideas and develop new techniques to study stellar rotation. More or less massive, more or lessevolved objects, however, can have averydi?erent rotation rate, structure and history. In recent years our understanding of the rotation of the Sun has greatly improved. The Sun has a well-known large-scale rotation, which can be m- sured thanks to visible features across the solar disk, such as sunspots, or via spectroscopy. In addition, several studies cast light on di?erential rotation in the convective zone and on meridional circulation in the radiative zone of the Sun. Even the rotation of the core of the Sun can now be studied thanks to various methods, such as dynamics of the gravitational moments and of course, helioseismology, through g-modes analysis. Moreover, the magnetic ?eld is strongly linked to the matter motions in the solar plasma. The solar magnetic ?eld can be measured only at the surface or in theupperlayers.Itistheproductoftheinternaldynamoorofthelocaldynamos if they exist – in any case magnetic ?eld and rotation cannot thus be separated.