On the line profile changes observed during the X2.2 class flare in the active region NOAA 11158

Abstract

The solar active region NOAA 11158 produced a series of flares during its passage through the solar disk. The first major flare (of class X2.2) of the current solar cycle occurred in this active region on 2011 February 15 around 01:50 UT. We have analyzed the Dopplergrams and magnetograms obtained by the Helioseismic and Magnetic Imager (HMI) instrument onboard Solar Dynamics Observatory (SDO) to examine the photospheric velocity and magnetic field changes associated with this flare. The HMI instrument provides highquality Doppler and magnetic maps of the solar disk at 0.5 arcsec spatial scale at a cadence of 45 s along with imaging spectroscopy. We have identified five locations of velocity transients in the active region during the flare. These transient velocity signals are located in and around the flare ribbons as observed by Hinode in Ca II H wavelength and the footpoints of hard X-ray enhancement in the energy range 12-25 keV from RHESSI. The changes in shape and width of two circular polarization states have been observed at the time of transients in three out of five locations. Forward modeling of the line profiles shows that the change in atmospheric parameters such as magnetic field strength, Doppler velocity and source function could explain the observed changes in the line profiles with respect to the pre-flare condition.

Investigating the Magnetic Imprints of Major Solar Eruptions with SDO/HMI High-cadence Vector Magnetograms

“…The RHESSI 25-50 keV hard X-ray (HXR) flux peaked at 01:54, two minutes before the SXR peak. The magnetic imprints and transients have been studied using routine HMI 45 s LoS and 720 s vector data (e.g., Kosovichev 2011;Wang et al 2012a;Sun et al 2012;Gosain 2012;Maurya et al 2012;Petrie 2013;Raja Bayanna et al 2014).…”

“…They are associated with continuum enhancement and Doppler-velocity transients (Kosovichev 2011). The observed left-and right-circularpolarization profiles appear to be distorted (Raja Bayanna et al 2014). HMI high-cadence Stokes data have been used to study magnetic transients too.…”

“…). The observed left-and right-circularpolarization profiles appear to be distorted (RajaBayanna et al 2014). HMI high-cadence Stokes data have been used to study magnetic transients too.…”

On the seismic emission in sunspots associated with Lorentz force changes accompanying major solar flares

“…It is believed that corresponding to the hard X-ray foot-points, high energetic charged particles can reach up to the photosphere and they can induce photospheric p-mode oscillations. However, in the flaring region/hard X-ray foot-point locations, it has been demonstrated that there could be distortions in the line profiles during the flares due to the change in the local thermodynamic conditions (Raja Bayanna, et al 2014). Therefore, we have looked for only those acoustically enhanced locations in the sunspots which are away from HXR footpoints and flare ribbons.…”

“…Hudson, Fisher & Welsch (2008) and Fisher, et al (2012) proposed that abrupt changes in the magnetic fields can lead to an impulsive change in Lorentz force, which is also known as "magnetic-jerk", and this can induce seismic emission in the sunspots. However, Raja Bayanna, et al (2014) observed distortions in the two circular polarization states of light, the Left Circular Polarization (LCP) and the Right Circular Polarization (RCP) observations in the flaring locations which showed transient changes in Doppler velocity and line-of-sight magnetic fields during an X-class flares, using the line profile observations from HMI instrument aboard the SDO space mission. They showed that observed transient changes in Doppler velocity and line-of-sight magnetic fields in flaring locations are prone to artefacts in the measurements.…”