Three-dimensional magnetic field topology in a region of solar coronal heating

Abstract

Flares and X-ray jets on the Sun arise in active regions where magnetic flux emerges from the solar interior amd interacts with the ambient magnetic field. The interactions are believed to occur in electric current sheets separating regions of opposite magnetic polarity. The current sheets located in the corona or upper chromosphere have long been thought to act as an important source of coronal heating, requiring their location in the corona or upper chromosphere. The dynamics and energetics of these sheets are governed by a complex magnetic field structure that, until now, has been difficult to measure. Here we report the determination of the full magnetic vector in an interaction region near the base of the solar corona. The observations reveal two magnetic features that characterize young active regions on the Sun: a set of rising magnetic loops and a tangential discontinuity of the magnetic field direction, the latter being the observational signature of an electric current sheet. This provides strong support for coronal heating models based on the dissipation of magnetic energy at current sheets.

The magnetic field in the solar atmosphere

“…Initial measurements of the LOS magnetic field were performed by Harvey and Hall (1971), Rüedi et al (1995) and Penn and Kuhn (1995) and the first vector magnetic field measurement by Rüedi et al (1996). Solanki et al (2003) applied the same method using the He I 10830 Å line, which is optically thin. Consequently, the measurements are related to different formation heights, following the fluctuating height of the coronal base.…”

Nonlinear force-free field extrapolation of the coronal magnetic field using the data obtained by the Hinode satellite

“…[5] Up to now, while many efforts have been devoted to the direct measurements of magnetic fields in the solar chromosphere and corona [e.g., Judge, 1998;Solanki et al, 2003;Lagg et al, 2004;Lin et al, 2004;Kramar et al, 2006;Trujillo Bueno and Asensio Ramos, 2007;Liu and Lin, 2008;Cargill, 2009;Frisch et al, 2009], the extrapolation based on NLFFF model is still a commonly used and necessary approach to understand the 3-D configuration of the coronal magnetic field. That is, the field can be reconstructed by solving the force-free and divergence-free differential equations (2) and (3) or equivalent equations (4) and (5), in which the observed photospheric vector magnetogram is taken as the bottom boundary condition.…”

Active Region Filaments Might Harbor Weak Magnetic Fields

“…Previous observations reinforce this idea because the photospheric and chromospheric magnetic field maps obtained using inversion techniques look astonishingly similar. The chromospheric maps look slightly more fuzzy because of the reduction in the gas pressure with height and the ensuing expansion, but no hint on any filamentary structure is detected (Solanki et al 2003;Xu et al 2010). We go one step forward and stand on the idea suggested by Asensio , proposing that what we see is in fact a combination of the two atmospheres.…”

“…One of the advantages of the multiplets is that the absorption of these lines is usually negligible in quiet regions, so that any absorption can be regarded as due to a levitating cloud at a certain height, which greatly simplifies the solution of the radiative transfer equation for polarized radiation SahalBrechot et al 1977;Trujillo Bueno & Asensio Ramos 2007). In particular, these spectral lines have been widely used for the study of solar prominences and filaments (e.g., Bommier et al 1981;Casini et al 2003;Merenda et al 2006;Orozco Suárez et al 2014;Martínez González et al 2015), the reconstruction of magnetic fields in flux emerging regions (Solanki et al 2003;Xu et al 2010) and in chromospheric spicules (e.g., López Ariste & Casini 2005;Centeno et al 2010;Martínez González et al 2012;Orozco Suárez et al 2015).…”