Three-dimensional magnetic field structure of a flux-emerging region in the solar atmosphere

by Rahul Yadav

Hosted by Stockholm University on April 16, 2020


We present spectropolarimetric analysis of a flux-emerging region (FER) in order to understand its magnetic and kinematic structure. Our spectropolarimetric observations, in the He i 10830Å spectral region, were recorded with the GRIS at the 1.5m aperture GREGOR telescope. A Milne–Eddington-based inversion code was employed to extract the photospheric information of the Si i spectral line, whereas the He i triplet line was analyzed with the Hazel code. The spectropolarimetric analysis of the Si i line reveals a complex magnetic structure near the vicinity of the FER, where a weak (350–600 G) and horizontal magnetic field was observed. In contrast to the photosphere, the analysis of the He i triplet presents a smooth variation of the magnetic field vector (ranging from 100 to 400 G) and velocities across the FER. Moreover, we find supersonic downflows of ∼40 km/s appearing near the foot points of loops connecting two pores of opposite polarity, whereas strong upflows of 22 km/s appear near the apex of the loops. Furthermore, nonforce-free field extrapolations were performed separately at two layers in order to understand the magnetic field topology of the FER. The reconstructed loops using photospheric extrapolations along an arch filament system have a maximum height of ∼10.5 Mm from the solar surface with a foot-point separation of ∼19 Mm, whereas the loops reconstructed using chromospheric extrapolations reach around ∼8.4 Mm above the solar surface with a foot-point separation of ∼16 Mm at the chromospheric height. The magnetic topology in the FER suggests the presence of small-scale loops beneath the large loops. Under suitable conditions, due to magnetic reconnection, these loops can trigger various heating events in the vicinity of the FER.

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