Rapid Transition of Uncombed Penumbrae to Faculae during Large Flares

Abstract

In the past two decades, the complex nature of sunspots has been disclosed with high-resolution observations. One of the most important findings is the "uncombed" penumbral structure, where a more horizontal magnetic component carrying most of Evershed Flows is embedded in a more vertical magnetic background (Solanki & Montavon 1993). The penumbral bright grains are locations of hot upflows and dark fibrils are locations of horizontal flows that are guided by nearly horizontal magnetic field. On the other hand, it was found that flares may change the topology of sunspots in $\delta$ configuration: the structure at the flaring polarity inversion line becomes darkened while sections of peripheral penumbrae may disappear quickly and permanently associated with flares (Liu et al. 2005). The high spatial and temporal resolution observations obtained with Hinode/ SOT provide an excellent opportunity to study the evolution of penumbral fine structure associated with major flares. Taking advantage of two near-limb events, we found that in sections of peripheral penumbrae swept by flare ribbons, the dark fibrils completely disappear, while the bright grains evolve into faculae that are signatures of vertical magnetic flux tubes. The corresponding magnetic fluxes measured in the decaying penumbrae show stepwise changes temporally correlated with the flares. These observations suggest that the horizontal magnetic field component of the penumbra could be straightened upward (i.e., turning from horizontal to vertical) due to magnetic field restructuring associated with flares, which results in the transition of penumbrae to faculae.

9 pages, 8 figures. Published in ApJ

References in corpus (9)

• The Solar Optical Telescope for the Hinode Mission: An Overview
• Penumbral structure and outflows in simulated sunspots
• Magnetostatic penumbra models with field-free gaps
• Two-dimensional spectroscopy of a sunspot. III Thermal and kinematic structure of the penumbra at 0.5"
• Spectropolarimetry of a decaying sunspot penumbra
• Coronal Implosion and Particle Acceleration in the Wake of a Filament Eruption
• Are there field-free gaps near tau=1 in sunspot penumbrae?
• Penumbral models in the light of Hinode spectropolarimetric observations
• Disintegration of Magnetic Flux in Decaying Sunspots as Observed with the Hinode SOT

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• Multi-wavelength Study of Transition Region Penumbral Subarcsecond Bright Dots Using IRIS and NST
• The formation and decay of sunspot penumbra in Active Region NOAA 12673
• The Decay of Two Adjacent Sunspots Associated with Moving Magnetic Features
• Erupting Magnetic Flux Rope Affects Running Penumbral Waves
• The Decay Process of an α-configuration Sunspot
• Back Reaction of the Untwisting Solar Corona Scars Sunspots