The Influence Of Solar Flares On The Structure Of Sunspots In The Photosphere

Rapid transformations of sunspot structures usually can be observed during the flare eruption.However,it is still controversial that if the transformations are induced by the flare eruption or not.In this paper,we present the observations and analysis of the reversal transformations of sunspot in two flare events,proving that the coronal flare eruption can affect the sunspot structures in the photosphere.In the case of the flare SOL2015-06-25T08:16(M7.9),we reported that the originally decayed penumbra showed a sudden reappearance along the flaring polarity inversion line(PIL).On the other hand,the small umbra,where the reappearing penumbra rooted,had a sudden northeastward motion,toward the north part of a large sunspot located in the other side of PIL.These observations can be well understood as a result of coronal fields contraction,which can be deduced from the nonlinear force-free field extrapolation model.In the case of the flare SOL2013-11-03T05:22(M5.0),we reported that a large penumbral area experiencing two kinds of transformations during the eruption.One penumbral segment decayed and transformed into a small pore when swept by the flare ribbon.At the same time,an adjacent penumbral segment expanded permeating into the granular area along the flaring magnetic polarity inversion line.EUV and X-ray observations indicated that the penumbral enhancement area was close to the flare center,while the penumbral decay area was on the relatively outer side.By tracking the magnetic motions and local magnetic field changes,we found that the magnetic transformations within two regions were totally different during the flare.The central penumbral enhancement area was accompanied by the field collapsing down,whereas the outer penumbral decay area was associated with the field lifting up towards the upper flare center.Particularly,following the uplift motion of the magnetic fields in the outer region,the magnetic flux in the decaying penumbra decreased and that in the forming pore subsequently increased.These results implied that the rearrangement of magnetic field during the flare would be the reason that resulted in the variations of the sunspot structures.