Editorial: Coronal Magnetometry

Sarah E. Gibson, Laurel A. Rachmeler, Stephen M. White
2017 Frontiers in Astronomy and Space Sciences  
Editorial on the Research Topic Coronal Magnetometry Magnetism defines the complex and dynamic solar corona. It determines the magnetic loop structure that dominates images of the corona, and stores the energy necessary to drive coronal eruptive phenomena and flare explosions. At great heights the corona transitions into the everoutflowing solar wind, whose speed and three-dimensional morphology are controlled by the global coronal magnetic field. Coronal magnetism is thus at the heart of any
more » ... the heart of any understanding of the nature of the corona, and essential for predictive capability of how the Sun affects the Earth. Such an understanding will ultimately come from knowing the time-evolving vector magnetic field throughout the solar corona. Given this knowledge, it becomes possible to determine where magnetic free energy is stored, what triggers the eruptive events that release this energy, where solar energetic particles are accelerated and how they propagate, and how coronal mass ejection (CME) internal magnetic structure evolves in response to interactions with the surrounding corona and solar wind. Until recently, our knowledge of magnetism in the corona was primarily limited to extrapolations of solar surface observations in conjunction with purely morphological coronal observations. There are several reasons that obtaining more direct observations of the coronal magnetic field is difficult; foremost among them is that the corona is optically thin and relatively dim compared to the solar disk. However, current and planned coronal polarimetric measurements are changing this paradigm, making the development of coronal magnetometric techiques a priority. Coronal magnetometry is a subject that requires a concerted effort to draw together the different strands of research happening around the world. Each method provides some information about the field, but none of them can be used to determine the full 3D field structure in the full volume of the corona. Thus, we need to combine them to understand the full picture. The purpose of this Frontiers Research Topic on Coronal Magnetometry is to provide a forum for comparing and coordinating these research methods. We now briefly summarize the papers it contains. A key development of recent years has been the availability of coronal polarimetric measurements, in particular at visible and infrared wavelengths. Dima et al. presents a method for combining linear-polarization measurements from near-infrared permitted and forbidden coronal emission lines to calculate the coronal vector magnetic field. Raouafi et al. similarly argues for multiwavelength linear-polarization diagnostics, using forward modeling of global MHD models to demonstrate the complementary diagnostic power of ultraviolet and infrared lines. Moving away from polarimetric measurements, Bemporad et al. discusses the extent to which the magnetic field strength of CMEs in the outer corona might be deduced from white-light and ultraviolet observations assumed to correspond to shock fronts. Observations of both coronal morphologies and thermal plasma properties contribute clues to the nature of the underlying magnetic structure. Jibben et al. presents a case study, and Bak-Stȩślicka et al. presents a statistical analysis of thermal and velocity structure within quiescent
doi:10.3389/fspas.2017.00003 fatcat:jrdfdyflpzhkbbfgmsgsrpfx6i