Sustained heating of the chromosphere and transition region over a sunspot light bridge

Abstract

Sunspot light bridges (LBs) exhibit a wide range of short-lived phenomena in the chromosphere and transition region. In contrast, we use here data from the Multi-Application Solar Telescope (MAST), the Interface Region Imaging Spectrograph (IRIS), Hinode, the Atmospheric Imaging Assembly (AIA), and the Helioseismic and Magnetic Imager (HMI) to analyze the sustained heating over days in an LB in a regular sunspot. Chromospheric temperatures were retrieved from the the MAST Ca II and IRIS Mg II lines by nonlocal thermodynamic equilibrium inversions. Line widths, Doppler shifts, and intensities were derived from the IRIS lines using Gaussian fits. Coronal temperatures were estimated through the differential emission measure, while the coronal magnetic field was obtained from an extrapolation of the HMI vector field. At the photosphere, the LB exhibits a granular morphology with field strengths of about 400 G and no significant electric currents. The sunspot does not fragment, and the LB remains stable for several days. The chromospheric temperature, IRIS line intensities and widths, and AIA 171 Åand 211 Åintensities are all enhanced in the LB with temperatures from 8000 K to 2.5 MK. Photospheric plasma motions remain small, while the chromosphere and transition region indicate predominantly red-shifts of 5-20 km/s with occasional supersonic downflows exceeding 100 km/s. The excess thermal energy over the LB is about 3.2x10^26 erg and matches the radiative losses. It could be supplied by magnetic flux loss of the sunspot (7.5x10^27 erg), kinetic energy from the increase in the LB width (4x10^28 erg), or freefall of mass along the coronal loops (6.3x10^26 ,erg).

Accepted for publication in The Astrophysical Journal; 24 pages, 15 figures, 3 tables, Appendix with 3 figures

References in corpus (21)

• The Solar Optical Telescope for the Hinode Mission: An Overview
• Thermal Diagnostics with the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory: A Validated Method for Differential Emission Measure Inversions
• An Open Source, Massively Parallel Code for Non-LTE Synthesis and Inversion of Spectral Lines and Zeeman-induced Stokes Profiles
• Recovering Thermodynamics from Spectral Profiles observed by IRIS: A Machine and Deep Learning Approach
• Modeling the Dispersal of an Active Region: Quantifying Energy Input into the Corona
• The signature of chromospheric heating in Ca II H spectra
• Small-scale chromospheric jets above a sunspot light bridge
• The Lightweaver Framework for NLTE Radiative Transfer in Python
• Observational study of chromospheric heating by acoustic waves
• Heating of the solar chromosphere in a sunspot light bridge by electric currents
• Effects of Cowling Resistivity in the Weakly-Ionized Chromosphere
• Narrow-Band Imaging System for the Multi-application Solar Telescope at Udaipur Solar Observatory: Characterization of Lithium Niobate Etalons
• On-disk solar coronal condensations facilitated by magnetic reconnection between open and closed magnetic structures
• The formation of an atypical sunspot light bridge as a result of large-scale flux emergence
• Solar Magnetic Carpet II: Coronal Interactions of Small-Scale Magnetic Fields
• IRIS observations of chromospheric heating by acoustic waves in solar quiet and active regions
• Structure of sunspot light bridges in the chromosphere and transition region
• The magnetic topology of the inverse Evershed flow
• Radiative losses in the chromosphere during a C-class flare
• Light Bridges Can Suppress the Formation of Coronal Loops
• Homologous flaring activity over a sunspot light bridge in an emerging active region

Cited by in corpus (1)

• On the formation height of low-corona and chromospheric channels of the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO)