New method makes magnetic maps of the solar corona

The twisting, ever-shifting and metrically elusive magnetic field of the Sun’s ephemeral outer atmosphere can be mapped using near-infrared observations of the solar corona. The method, presented in a new study, could be used to greatly enhance the understanding of conditions in this poorly studied region of the Sun. The solar corona – the tenuous outermost layer of the Sun’s atmosphere – consists of a hot and highly diffuse plasma halo extending thousands of kilometers above the star’s burning surface. Bound by the strong magnetic fields that thread throughout the solar atmosphere, the corona plays a key role in much of the solar activity that directly impacts Earth and the greater Solar System. It’s generally accepted that the highly dynamic magnetic fields in this region strongly influence many of the solar atmosphere’s complex physical processes. However, unlike those of the magnetic fields at the Sun’s surface, meaningful observations of the coronal magnetic field are limited, and direct measurements are challenging to obtain. Here, Zihao Yang and colleagues used unique near-infrared imaging spectroscopy observations from the Coronal Multi-channel Polarimeter (CoMP) to determine the electron density and magnetohydrodynamic wave speed in the solar corona. Combining these measurements allowed Yang et al. to derive maps of the magnetic field across the entire observable corona. The results demonstrate that imaging spectroscopy can be used to determine the coronal magnetic field. While the authors report that the technique cannot be applied to regions affected by solar eruptions or other transient large-scale magnetic disruptions, it could be used to produce routine magnetic field maps similar to those available for the Sun’s surface.

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http://dx.doi.org/10.1126/science.abb4462

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