Solar Surface Magnetism

Observations of the solar magnetic field are largely confined to the radiation emitted from the photosphere, the thin layer of the solar atmosphere which we call "the solar surface". It is from solar surface observations that we must infer the internal structure and the internal magnetohydrodynamic processes that lead to the multitude of fascinat ing phenomena of solar magnetic activity, and from solar surface observations we must also infer the interplay of convection and magnetism that regulates field dispersal, drives the heating of the outer-atmospheric plasma, and generates the solar wind. There is much to be learned from solar surface magnetism in physics and astrophysics; currently, there are rapid developments in this exciting field. The workshop of which this volume contains the proceedings aimed at a synthesis between observers and theorists, both with regard to the discrete elements that are the building blocks of solar magnetism and with regard to the larger-scale spatial and temporal patterns in which the magnetic elements emerge and disappear. The workshop was held during November 1-5, 1993 in Soesterberg, The Netherlands. The fifty participants took a very active part in making the workshop quite a lively one. The articles in these proceedings cover most of the oral and poster presentations, excepting a dozen soon to be published elsewhere.

The COSPAR Colloquium on Solar-Terrestrial Magnetic Activity and Space Environment (STMASE) was held in the National Astronomy Observatories of Chinese Academy of Sciences (NAOC) in Beijing, China in September 10-12, 2001. The meeting was focused on five areas of the solar-terrestrial magnetic activity and space environment studies, including study on solar surface magnetism; solar magnetic activity, dynamical response of the heliosphere; space weather prediction; and space environment exploration and monitoring. A hot topic of space research, CMEs, which are widely believed to be the most important phenomenon of the space environment, is discussed in many papers. Other papers show results of observational and theoretical studies toward better understanding of the complicated image of the magnetic coupling between the Sun and the Earth, although little is still known little its physical background. Space weather prediction, which is very important for a modern society expanding into out-space, is another hot topic of space research. However, a long way is still to go to predict exactly when and where a disaster will happen in the space. In that sense, there is much to do for space environment exploration and monitoring. The manuscripts submitted to this Monograph are divided into the following parts: (1) solar surface magnetism, (2) solar magnetic activity, (3) dynamical response of the heliosphere, (4) space environment exploration and monitoring; and (5) space weather prediction. Papers presented in this meeting but not submitted to this Monograph are listed by title as unpublished papers at the end of this book.

Starting in 1995 numerical modeling of the Earth’s dynamo has ourished with remarkable success. Direct numerical simulation of convection-driven MHD- ow in a rotating spherical shell show magnetic elds that resemble the geomagnetic eld in many respects: they are dominated by the axial dipole of approximately the right strength, they show spatial power spectra similar to that of Earth, and the magnetic eld morphology and the temporal var- tion of the eld resembles that of the geomagnetic eld (Christensen and Wicht 2007). Some models show stochastic dipole reversals whose details agree with what has been inferred from paleomagnetic data (Glatzmaier and Roberts 1995; Kutzner and Christensen 2002; Wicht 2005). While these models represent direct numerical simulations of the fundamental MHD equations without parameterized induction effects, they do not match actual pla- tary conditions in a number of respects. Speci cally, they rotate too slowly, are much less turbulent, and use a viscosity and thermal diffusivity that is far too large in comparison to magnetic diffusivity. Because of these discrepancies, the success of geodynamo models may seem surprising. In order to better understand the extent to which the models are applicable to planetary dynamos, scaling laws that relate basic properties of the dynamo to the fundamental control parameters play an important role. In recent years rst attempts have been made to derive such scaling laws from a set of numerical simulations that span the accessible parameter space (Christensen and Tilgner 2004; Christensen and Aubert 2006).

This paper describes the magnetic field configurations observed in the solar atmosphere including the corona and the solar wind. The techniques for observing solar magnetic fields are briefly reviewed. The significance of Alfven waves in transporting energy is stressed. (Author).

Discusses recent advances and new problems in the exploration of the Sun's interior structure, solar dynamics and dynamo, mechanisms of sunspot and active regions formation, sources of solar irradiance variations and links between the subsurface dynamics, flaring and CME activity. NASA's Solar Dynamics Observatory (SDO) mission has provided a large amount of new data on solar dynamics and magnetic activities during the rising phase of the current and highly unusual solar cycle. These data are complemented by the continuing SOHO mission and by ground-based observatories that include the GONG helioseismology network and the New Solar Telescope. Also, the observations are supported by realistic numerical simulations on supercomputers. This unprecedented amount of data provides a unique opportunity for multi-instrument investigations that address fundamental problems of the origin of solar magnetic activity at various spatial and temporal scales. This book demonstrates that the synergy of high-resolution multi-wavelength observations and simulations is a key to uncovering the long-standing puzzles of solar magnetism and dynamics. This volume is aimed at researchers and graduate students active in solar physics and space science. Originally published in Solar Physics journal, Vol. 287/1-2, 2013.

How are large-scale magnetic fields generated in the Sun in self-excited dynamo processes? And how are magnetic structures spontaneously formed in the Sun and how do they interact with the convective flows, storage and release of magnetic energy? These are just several of the fundamental questions answered in this timely review of our understanding of solar magnetic fields. This volume collects together review articles and research papers from an international conference, held in Freiburg, Germany, dedicated to the study of magnetic fields in the Sun. From large-scale patterns and global dynamo action to tiny flux tubes, from the overshoot layer below the convection zone up to the corona, and from instrumental problems and theoretical methods to the latest ground-based and satellite observations, this volume provides an essential review of our knowledge to date for graduate students and researchers.

Comprised of lectures for an intensive course held at the Newton Institute in Cambridge, as part of a NATO Advanced Study Institute, the topics covered within this volume include planetary and solar dynamos, fast dynamos, and the use of symmetry principles to derive evolution equations.