Magnetohydrostatic modelling of the solar atmosphere: Test and application

<div><span><span lang="en-US">Both magnetic field and plasma play important roles in activities in the solar atmosphere. Unfortunately only the magnetic fields in the photosphere are routinely measured precisely. We aim to extrapolate these photospheric </span></span><span><span lang="en-US">vector magnetograms upwards into  the solar atmosphere. In this work </span><span lang="en-US">we are mainly interested in reconstructing the upper solar photosphere </span><span lang="en-US">and chromosphere. In these layers magnetic and non-magnetic forces are equally important. Consequently we have to compute an equilibrium of plasma </span></span><span><span lang="en-US">and magnetic forces with a magnetohydrostatic model. A optimization approach which minimize a functional defined by the magnetohydrostatic equations is used in the model. In this talk/poster, I will present a strict test of the new code with a radiative MHD simulation and its first application to a high resolution vector magnetogram measured by SUNRISE/IMaX.</span></span></div>

Relative magnetic helicity dissipation during the major flares

<p>    Magnetic helicity is conserved in ideal magnetic fluid and is still approximately conserved in the process of fast magnetic reconnection when the magnetic Reynolds number is large enough. We can derive the magnetic helicity injecting into corona from the magnetic helicity flux through photoshpere. A statistical research is carried out to investigate the dissipation of magnetic helicity during the major flares. We choose 69M-up flares from 16 major flare-productive active regions in 24th cycle to research the helicity in corona. Among these flares, 19 is X-up flares. We utilize Differential Affine Velocity Estimator for Vector Magnetograms (DAVE4VM) and 12-min successive vector magnetograms from Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO) to derive the flux of magnetic helicity through photosphere. At the same time, we extrapolate the vector magnetic field in corona to calculate the relative helicity by the suppose of Non-linear Force Free Field (NLFFF). The calculation window is 12-18 minutes before and after flares. A well correlation is shown between the magnetic free energy and magnetic helicity, the threshold of triggering M-up flare is the change of magnetic helicity above 2×10<sup>42</sup>Mx<sup>2</sup> and the change of magnetic free energy above 3 × 10<sup>31</sup>erg . Considering one fifth of magnetic helicity injecting into corona, the dissipation of magnetic helicity during the flares is 6-7 % , which is corresponding to the result of previous numerical simulation results, which strongly support that the magnetic helicity is approximate conserved during the major flares.</p>

The origin of two X-class flares in active region NOAA 12673

Flare-prolific active region NOAA 12673 produced consecutive X2.2 and X9.3 flares on the 6 September 2017. To scrutinize the morphological, magnetic, and horizontal flow properties associated with these flares, a seven-hour time series was used consisting of continuum images, line-of-sight and vector magnetograms, and 1600 Å UV images. These data were acquired with the Helioseismic and Magnetic Imager (HMI) and the Atmospheric Imaging Assembly (AIA). The white-light flare emission differed for both flares, while the X2.2 flare displayed localized, confined flare kernels, the X9.3 flare exhibited a two-ribbon structure. In contrast, the excess UV emission exhibited a similar structure for both flares, but with larger areal extent for the X9.3 flare. These two flares represented a scenario in which the first confined flare acted as precursor, setting up the stage for the more extended flare. Difference maps for continuum and magnetograms revealed locations of significant changes, that is, penumbral decay and umbral strengthening. The curved magnetic polarity inversion line in the δ-spot was the fulcrum of most changes. Horizontal proper motions were computed using the differential affine velocity estimator for vector magnetograms (DAVE4VM). Persistent flow features included (1) strong shear flows along the polarity inversion line, where the negative, parasitic polarity tried to bypass the majority, positive-polarity part of the δ-spot in the north, (2) a group of positive-polarity spots, which moved around the δ-spot in the south, moving away from the δ-spot with significant horizontal flow speeds, and (3) intense moat flows partially surrounding the penumbra of several sunspots, which became weaker in regions with penumbral decay. The enhanced flare activity has its origin in the head-on collision of newly emerging flux with an already existing regular, α-spot. Umbral cores of emerging bipoles were incorporated in its penumbra, creating a δ-configuration with an extended polarity inversion line, as the parasitic umbral cores were stretched while circumventing the majority polarity.