Study of Rapid Formation of a Delta Sunspot Associated with the 2012 July 2 C7.4 Flare Using High-resolution Observations of New Solar Telescope

Abstract

Rapid, irreversible changes of magnetic topology and sunspot structure associated with flares have been systematically observed in recent years. The most striking features include the increase of horizontal field at the polarity inversion line (PIL) and the co-spatial penumbral darkening. A likely explanation of the above phenomenon is the back reaction to the coronal restructuring after eruptions: a coronal mass ejection carries the upward momentum while the downward momentum compresses the field lines near the PIL. Previous studies could only use low resolution (above 1") magnetograms and white-light images. Therefore, the changes are mostly observed for X-class flares. Taking advantage of the 0.1" spatial resolution and 15s temporal cadence of the New Solar Telescope at Big Bear Solar Observatory, we report in detail the rapid formation of sunspot penumbra at the PIL associated with the C7.4 flare on 2012 July 2. It is unambiguously shown that the solar granulation pattern evolves to alternating dark and bright fibril structure, the typical pattern of penumbra. Interestingly, the appearance of such a penumbra creates a new delta sunspot. The penumbral formation is also accompanied by the enhancement of horizontal field observed using vector magnetograms from the Helioseismic and Magnetic Imager. We explain our observations as due to the eruption of a flux rope following magnetic cancellation at the PIL. Subsequently the re-closed arcade fields are pushed down towards the surface to form the new penumbra. NLFFF extrapolation clearly shows both the flux rope close to the surface and the overlying fields.

References in corpus (4)

• Photospheric flux cancellation and associated flux rope formation and eruption
• MHD Simulation of a Sigmoid Eruption of Active Region 11283
• The Relationship between the Sudden Change of the Lorentz Force and the Magnitude of Associated Flares
• Rapid Transition of Uncombed Penumbrae to Faculae during Large Flares

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• Structure and Evolution of Magnetic Fields Associated with Solar Eruptions (Invited Review)
• Sudden Photospheric Motion and Sunspot Rotation Associated with the X2.2 Flare on 2011 February 15
• Three-dimensional Magnetic Restructuring in Two Homologous Solar Flares in the Seismically Active NOAA AR 11283
• Magnetic Field Restructuring Associated with Two Successive Solar Eruptions
• Formation and Eruption of a Small Flux Rope in the Chromosphere Observed by NST, IRIS, and SDO
• Filament Eruption and Its Reformation Caused by Emerging Magnetic Flux
• Automatic Recognition of Sunspots in HSOS Full-Disk Solar Images
• Evolution of Photospheric Flow and Magnetic Fields Associated with The 2015 June 22 M6.5 Flare
• On the relationship between sunspot structure and magnetic field changes associated with solar flares
• A Survey of Changes in Magnetic Helicity Flux on the Photosphere During Relatively Low Class Flares
• Fast-growing SMBHs in Fast-growing Galaxies, at High Redshifts: the Role of Major Mergers as Revealed by ALMA
• On the nature of photospheric horizontal magnetic field increase in major solar flares