Horizontal flow fields observed in Hinode G-band images III. The decay of a satellite sunspot and the role of magnetic flux removal in flaring

Abstract

The flare-prolific active region NOAA 10930 offered both a developing delta-spot and a decaying satellite sunspot of opposite polarity. The objective of this study is to characterize the photometric decay of the satellite sunspot and the evolution of photospheric and chromospheric horizontal proper motions in its surroundings. We apply the local correlation tracking technique to a 16-hour time-series of Hinode G-band and CaIIH images and study the horizontal proper motions in the vicinity of the satellite sunspot on 2006 December 7. Decorrelation times were computed to measure the lifetime of solar features in intensity and flow maps. We observed shear flows in the dominant umbral cores of the satellite sunspot. These flows vanished once the penumbra had disappeared. This slow penumbral decay had an average rate of 152Mm2/day over an 11-hour period. Typical lifetimes of intensity features derived from an autocorrelation analysis are 3-5min for granulation, 25-35min for G-band bright points, and up to 200-235min for penumbrae, umbrae, and pores. Long-lived intensity features (i.e., the dominant umbral cores) are not related to long-lived flow features in the northern part of the sunspot, where flux removal, slowly decaying penumbrae, and persistent horizontal flows of up to 1 km/s contribute to the erosion of the sunspot. Finally, the restructuring of magnetic field topology was responsible for a homologous M2.0 flare, which shared many characteristics with an X6.5 flare on the previous day. Notwithstanding the prominent role of delta-spots in flaring, we conclude based on the decomposition of the satellite sunspot, the evolution of the surrounding flow fields, and the timing of the M2.0 flare that the vanishing magnetic flux in the decaying satellite sunspot played an instrumental role in triggering the homologous M2.0 flare and the eruption of a small Halpha filament.

11 pages, 8 figures, 3 tables, accepted for publication in Astronomy and Astrophysics

References in corpus (5)

• Non-linear force-free field modeling of a solar active region around the time of a major flare and coronal mass ejection
• Horizontal flow fields observed in Hinode G-band images II. Flow fields in the final stages of sunspot decay
• Rapid Transition of Uncombed Penumbrae to Faculae during Large Flares
• Decorrelation Times of Photospheric Fields and Flows
• Rapid Disappearance of Penumbra-Like Features Near a Flaring Polarity Inversion Line: The Hinode Observations

Cited by in corpus (6)

• Slipping Magnetic Reconnection of Flux Rope Structures as a Precursor to an Eruptive X-class Solar Flare
• Counter-streaming flows in a giant quiet-Sun filament observed in the extreme ultraviolet
• Horizontal flow fields in and around a small active region-- The transition period between flux emergence and decay
• Horizontal flow fields observed in Hinode G-band images IV. Statistical properties of the dynamical environment around pores
• Evolution of Photospheric Flow and Magnetic Fields Associated with The 2015 June 22 M6.5 Flare
• Background-subtracted Solar Activity Maps