Title: Magnetic Flux Emergence and Formation of Magnetic Flux Ropes
Author: B. C. Low
Affil: HAO/NCAR
Email: Low@hao.ucar.edu
Abstract: This talk will address several observational and theoretical issues relating to the emergence of a twisted magnetic field through the photosphere to form a twisted magnetic flux rope in the atmosphere above. Although the detailed physics is complex some general hydromagnetic points can be made about this process. Among these is the interplay between dissipative MHD liberating magnetic energy by magnetic reconnection, and ideal MHD liberating magnetic energy in large-scale expulsions of magnetized plasma out of the solar corona. The roles of flares and coronal mass ejections from this physical view point become complementary in the evolution of the solar corona on the time scale of a solar cycle. This view point also relates the corona to the solar dynamo via the observed perference of the sign of magnetic helicity in the two solar hemisphere.
Title: Magnetic Field Distributions and Variations in Coronal Structures
Author: Karel Schrijver
Affil: Lockheed Martin Advanced Technology Center
Email: schryver@lmsal.com
Abstract: Despite having scrutinized the solar corona for decades, it is still full of surprises. Ongoing missions like TRACE, SOHO, and YOHKOH have shattered the traditional view of the quiescent corona as an environment that is primarily made up of slowly evolving loop atmospheres, that are heated rather uniformly and persistently to a narrow temperature range, in which rapid changes occur only during field emergence, flares, and filament eruptions. All of these assumptions have been demonstrated to be erroneous, so that our view now shifts to a corona in which both the outer-atmospheric heating and the evolution of the magnetic field are intrinsically dynamic, with a wide range of temperatures existing side by side, and with the heating far from steady or uniform.
In this presentation, I will show and discuss examples of the dynamic evolution of the field and of the loop atmospheres embedded in it, and their relationship to the photospheric magnetic field and chromospheric phenomena. I will also address how the properties of coronal structures can be used to identify candidate coronal heating mechanisms.
Title: Multi-Wavelength Studies of CME Onsets
Author: Lidia van Driel
Affil: Observatoire de Paris, France, MSSL, UCL, UK; Konkoly Obs. Hungary;
Email: Lidia.vanDriel@obspm.fr
Authors: Pascal Demoulin (1), Cristina H.Mandrini (4), Marcelo Lopez-Fuentes (4), Lucie M. Green (2), BarbaraThompson (5), Simon Plunkett (6)
Affils: (1) Observatoire de Paris, DASOP, 92195 Meudon Cedex, France; (2) MSSL, University College London, Holmbury St. Mary, Dorking, Surrey, RH5 6NT, UK;(3) Konkoly Observatory, 1525 Budapest, Pf. 67, Hungary(4) IAFE, CC.67, Suc.28, 1428 Buenos Aires, Argentina; (5) NASA/Goddard SFC, Greenbelt, MD 20771, USA; (6) NRL, Washington, DC 20375, USA;
Abstract: Since CMEs are fundamentally magnetic phenomena, understanding processes like CME build-up and onset must be based on analyses of the magnetic evolution and topology of the CME source region and its environment. Special attention should be payed to evolution of the magnetic helicity. CMEs appear to be the means by which the helicity accumulated by twisted flux emergence and the differential rotation can be shed by the Sun, thus the onset of CMEs may indicate that a threshold has been reached in the system. Through a series of magnetic extrapolations (in lfff approximation) matched with observed coronal loops we show the magnetic helicity evolution of two active regions from craddle to grave (July-Dec. 1996, Nov. 1997-March 1998) together with the evolution of their CME productivity and compute the relative importance of helicity injected by the differential rotation and flux emergence. Besides the slow CME build-up we show a few typical short-term magnetic precursor events. We discuss the role of large-scale magnetic fields in the CME process. We present multiwavelength case-studies, using Yohkoh, SOHO and TRACE data, of CME events observed in these CME-prolific active regions initiated at their different magnetic evolutionary stages, in order to provide clues for understanding conditions for high CME productivity. Such work may eventually improve our ability to forecast CMEs.
Title: Evolution and eruptions of twisted coronal structures
Author: Sarah Gibson
Affil: NCAR/HAO
Email: sgibson@hao.ucar.edu
Abstract: Observations of coronal mass ejections (CMEs) show distinctly twisted structures, providing a clue to the nature of the magnetic field underlying them. Recent studies have shown that regions observed to possess a large degree of twist (such as S-shaped, or "sigmoid" active regions) are statistically more likely to erupt. I will show detailed multi-wavelength observations of one particular sigmoid region (AR8668, August 17-26, 1999), and discuss possible interpretations of its action-packed evolution as it crossed the solar disk. I will then consider the magnetic structure of such sigmoid regions, in terms of observations and also theoretical magnetic models.