Magnetic and Dynamical Photospheric Disturbances Observed During an M3.2 Solar Flare

Abstract

This letter reports on a set of full-Stokes spectropolarimetric observations in the near infrared He i 10830Å spectral region covering the pre-, flare, and post-flare phases of an M3.2 class solar flare. The flare originated on 2013 May 17 and belonged to active region NOAA 11748. We detected strong He i 10830Å emission in the flare. The red component of the He i triplet peaks at an intensity ratio to the continuum of about 1.86. During the flare, He i Stokes V is substantially larger and appears reversed compared to the usually larger Si i Stokes V profile. The photospheric Si i inversions of the four Stokes profiles reveal the following:(1) the magnetic field strength in the photosphere decreases or is even absent during the flare phase, as compared to the pre-flare phase. However, this decrease is not permanent. After the flare the magnetic field recovers its pre-flare configuration in a short time (i.e., in 30 minutes after the flare).(2) In the photosphere, the line-of-sight velocities show a regular granular up-and down-flow pattern before the flare erupts. During the flare, upflows (blueshifts) dominate the area where the flare is produced. Evaporation rates of ∼ 10 −3 and ∼ 10 −4 g cm −2 s −1 have been derived in the deep and high photosphere, respectively, capable of increasing the chromospheric density by a factor of two in about 400 seconds.

Flare-induced changes of the photospheric magnetic field in aδ-spot deduced from ground-based observations

“…On the other hand, we cannot exclude that the spatial resolution of our observation was insufficient to re-solve the probably very subtle flare-induced velocity changes. Kuckein et al (2015a) reported on newly appearing upflows in response to an M3.2 flare. Although their data were taken with the same instrument, the upflows were stronger next to the PIL rather than along it.…”

Capabilities of bisector analysis of the Si I 10 827 Å line for estimating line-of-sight velocities in the quiet Sun

“…Rezaei & Beck 2015), sunspots and pores (e.g. Xu et al 2010;Joshi 2014), flares (Judge et al 2014;Kuckein et al 2015), or independently, for example, in small-scale magnetic bright points (Kuckein 2019) or sunspots (e.g. Rezaei et al 2012;Felipe et al 2016;Orozco Suárez et al 2017).…”

Spectropolarimetric Inversions of the Ca ii 8542 Å Line in an M-class Solar Flare

“…Spectropolarimetric data of the flare in the Ca II 8542 and He II 10830 Å lines have been analyzed in several works (Penn & Kuhn 1995;Kleint & Judge 2011;Sasso et al 2011;Judge et al 2014Judge et al , 2015Kuckein et al 2015aKuckein et al , 2015b. Using photographic recordings of Stokes I and V profiles in the Ca II H line, Martinez Pillet et al (1990) derived a value of 820(±40)G for B LOS using the weak-field approximation (WFA).…”