Rapid Penumbral Decay Associated With Solar Flare

Solar flares are generally believed to be a consequence of a sudden magnetic energy release due to magnetic reconnection or ideal MHD instabilities in the corona, and the resultant coronal magnetic-field reconstruction could impact the solar surface and interior. Observationally, rapid and irreversible changes in sunspot structure associated with flares have been studied for the past two decades. The fundamental theory to explain these observations is the magnetic implosion summarized by Hudson et al., i.e., the energy release from the coronal field can result in so-called back reaction on the solar surface and interior.This paper present observations of the violent changes in photospheric structures associated with an X1.1 flare, which occurred in a compact ?-configuration region in the following part of AR 11890 on 2013 November 8. In both central and peripheral penumbra regions of the small ?sunspot, these changes took place abruptly and permanently in the reverse direction during the flare: the inner/outer penumbra darkened/disappeared, where the magnetic fields became more horizontal/vertical. Particularly, the Lorentz force changes in the central/peripheral region had a downward/upward and inward direction, meaning that the local pressure from the upper atmosphere was enhanced/released. It indicates that the LF changes might be responsible for the penumbra changes. These observations can be well explained as the photospheric response to the coronal field reconstruction within the framework of the magnetic implosion theory and the back reaction model of flares.