Flare Reconnection-driven Magnetic Field and Lorentz Force Variations at the Sun’s Surface

Abstract

During eruptive flares, vector magnetograms show increasing horizontal magnetic field and downward Lorentz force in the Sun's photosphere around the polarity-inversion line. Such behavior has often been associated with the implosion conjecture and interpreted as the result of either momentum conservation while the eruption moves upward, or of the contraction of flare loops. We characterize the physical origin of these observed behaviors by analyzing a generic 3D MHD simulation of an eruptive flare. Even though the simulation was undesigned to recover the magnetic field and Lorentz force properties, it is fully consistent with them, and it provides key additional informations to understand them. The area where the magnetic field increases gradually develops between current ribbons, which spread away from each other and are connected to the coronal region. This area is merely the footprint of the coronal postflare loops, whose contraction increases their shear field component and the magnetic energy density in line with the ideal induction equation. For simulated data, we computed the Lorentz force density map by applying the method used in observations. We obtained increase of the downward component of the Lorentz force density around the PIL -consistent with observations. However, this significantly differs from the Lorentz force density maps obtained directly from the 3D magnetic field and current. These results altogether question previous interpretations based on the implosion conjecture and momentum conservation with the CME, and rather imply that the observed increases in photospheric horizontal magnetic fields result from the reconnection-driven contraction of sheared flare-loops.

How flux feeding causes eruptions of solar magnetic flux ropes with the hyperbolic flux tube configuration?

“…As a result of the reconnection-driven contraction of the flare loops, the horizontal photospheric magnetic field B x increases accordingly (see Fig. 3(f)-3(h)), which is consistent with the simulation results in Barczynski et al (2019).…”

The role of small-scale surface motions in the transfer of twist to a solar jet from a remote stable flux rope

“…The sheared vec B that converges towards the PIL is a characteristic motion to create a BP. This pattern can also be seen in Barczynski et al (2019). It is due to the summed effects of: (i) the shear that creates a BP with vec B in the negative polarity pointing towards the positive polarity; and (ii) the asymmetry of the photospheric flux concentration with a stronger positive polarity (in the model and observations) which is due to the magnetic pressure pushing all the fields towards the (weaker) negative polarity.…”

Continuum Enhancements, Line Profiles, and Magnetic Field Evolution during Consecutive Flares

“…Recent observations of the magnetic field rearrangement in the photosphere after an M5.0 solar flare show that the inner penumbral enhancement around the flaring PIL area was accompanied by the field collapsing down, whereas the outer penumbral decay area was associated with the field lifting up toward the upper flare center . Contrarily, 3D simulations suggest that observed enhancement in the photospheric horizontal magnetic fields along the PIL results from the reconnection-driven contraction of sheared flare-loops, which increases the downward component of the Lorentz force density around the PIL (Barczynski et al 2019).…”