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In the past two decades, the complex nature of sunspots has been disclosedwith high-resolution observations. One of the most important findings is the"uncombed" penumbral structure, where a more horizontal magnetic componentcarrying most of Evershed Flows is embedded in a more vertical magneticbackground (Solanki & Montavon 1993). The penumbral bright grains are locationsof hot upflows and dark fibrils are locations of horizontal flows that areguided by nearly horizontal magnetic field. On the other hand, it was foundthat flares may change the topology of sunspots in $\delta$ configuration: thestructure at the flaring polarity inversion line becomes darkened whilesections of peripheral penumbrae may disappear quickly and permanentlyassociated with flares (Liu et al. 2005). The high spatial and temporalresolution observations obtained with Hinode/ SOT provide an excellentopportunity to study the evolution of penumbral fine structure associated withmajor flares. Taking advantage of two near-limb events, we found that insections of peripheral penumbrae swept by flare ribbons, the dark fibrilscompletely disappear, while the bright grains evolve into faculae that aresignatures of vertical magnetic flux tubes. The corresponding magnetic fluxesmeasured in the decaying penumbrae show stepwise changes temporally correlatedwith the flares. These observations suggest that the horizontal magnetic fieldcomponent of the penumbra could be straightened upward (i.e., turning fromhorizontal to vertical) due to magnetic field restructuring associated withflares, which results in the transition of penumbrae to faculae.

Rapid Transition of Uncombed Penumbrae to Faculae during Large Flares