Three-dimensional structure of a sunspot light bridge

Abstract

Active regions are the most prominent manifestations of solar magnetic fields; their generation and dissipation are fundamental problems in solar physics. Light bridges are commonly present during sunspot decay, but a comprehensive picture of their role in the removal of photospheric magnetic field is still missing. We study the three dimensional configuration of a sunspot and in particular its light bridge during one of the last stages of its decay. We present the magnetic and thermodynamical stratification inferred from full Stokes inversions of the photospheric Si I 10827 Å and Ca I 10839 Å lines obtained with the GREGOR Infrared Spectrograph of the GREGOR telescope at Observatorio del Teide, Tenerife, Spain. The analysis is complemented by a study of continuum images covering the disk passage of the active region, which are provided by the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory. The sunspot shows a light bridge with penumbral continuum intensity that separates the central umbra from a smaller umbra. We find that in this region the magnetic field lines form a canopy with lower magnetic field strength in the inner part. The photospheric light bridge is dominated by gas pressure (high-$\beta$), as opposed to the surrounding umbra where the magnetic pressure is higher. A convective flow is observed in the light bridge. This flow is able to bend the magnetic field lines and to produce field reversals. The field lines close above the light bridge and become as vertical and strong as in the surrounding umbra. We conclude that it develops because of two highly magnetized regions which come closer during the sunspot evolution.

Accepted for publication in A&A

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Cited by in corpus (19)

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• Three-dimensional magnetic structure of a sunspot: comparison of the photosphere and upper chromosphere
• Capabilities of bisector analysis of the Si I 10827 A line for estimating line-of-sight velocities in the quiet Sun
• Restoring process of sunspot penumbra
• Multiple Stokes I inversions to infer magnetic fields in the spectral range around Cr I 5782 Å
• Penumbral decay observed in active region NOAA 12585
• Sunspot penumbral filaments intruding into a light bridge and the resultant reconnection jets
• Signatures of the impact of flare ejected plasma on the photosphere of a sunspot light-bridge
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• Long-Term Evolution of Three Light Bridges Developed on the Same Sunspot
• Detection of emission in the Si i 1082.7 nm line core in sunspot umbrae
• Peculiarities of the Dynamics of Solar NOAA Active Region 12673
• Tracking downflows from the chromosphere to the photosphere in a solar arch filament system
• Light Bridges Can Suppress the Formation of Coronal Loops
• Standing MHD Waves in a Magnetic Slab Embedded in an Asymmetric Magnetic Plasma Environment: Surface Waves
• Various Activities above Sunspot Light Bridges in IRIS Observations: Classification and Comparison