Magnetic field inference in active region coronal loops using coronal rain clumps

Abstract

<p><em>[eng] Aims. We aim to infer information about the magnetic field in the low solar corona from coronal rain clumps using high-resolution</em></p><p><em>spectropolarimetric observations in the Ca ii 8542Å line obtained with the Swedish 1m Solar Telescope.</em></p><p><em>Methods. The weak-field approximation (WFA) provides a simple tool to obtain the line-of-sight component of the magnetic field</em></p><p><em>from spectropolarimetric observations. We adapted a method developed in a previous paper in order to assess the di erent conditions</em></p><p><em>that must be satisfied in order to properly use the WFA for the data at hand. We also made use of velocity measurements in order to</em></p><p><em>estimate the plane-of-the-sky magnetic field component, so that the magnetic field vector could be inferred.</em></p><p><em>Results. We have inferred the magnetic field vector from a data set totalling 100 spectral scans in the Ca ii 8542Å line, containing</em></p><p><em>an o -limb view of the lower portion of catastrophically cooled coronal loops in an active region. Our results, albeit limited by</em></p><p><em>the cadence and signal-to-noise ratio of the data, suggest that magnetic field strengths of hundreds of Gauss, even reaching up to</em></p><p><em>1000 G, are omnipresent at coronal heights below 9Mm from the visible limb. Our results are also compatible with the presence of</em></p><p><em>larger magnetic field values such as those reported by previous works. However, for large magnetic fields, the Doppler width from</em></p><p><em>coronal rain is not that much larger than the Zeeman width, thwarting the application of the WFA. Furthermore, we have determined</em></p><p><em>the temperature, T, and microturbulent velocity, $\csi$, of coronal rain clumps and o -limb spicules present in the same data set, and</em></p><p><em>we have found that the former ones have narrower T and distributions, their average temperature is similar, and coronal rain has</em></p><p><em>microturbulent velocities smaller than those of spicules.</em></p>