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).

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

References in corpus (44)

• The Interface Region Imaging Spectrograph (IRIS)
• The Solar Optical Telescope for the Hinode Mission: An Overview
• Heating of the Solar Chromosphere and Corona by Alfven Wave Turbulence
• Radiative MHD simulation of sunspot structure
• Thermal Diagnostics with the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory: A Validated Method for Differential Emission Measure Inversions
• Automated LASCO CME catalog for solar cycle 23: are CMEs scale invariant?
• An Open Source, Massively Parallel Code for Non-LTE Synthesis and Inversion of Spectral Lines and Zeeman-induced Stokes Profiles
• STiC -- A multi-atom non-LTE PRD inversion code for full-Stokes solar observations
• Coronal heating through braiding of magnetic field lines
• Numerical simulations of conversion to Alfven waves in sunspots
• Plasma Ejections from a Light Bridge in a Sunspot Umbra
• Alfvén Wave Dissipation in the Solar Chromosphere
• Continuum Enhancements in the Ultraviolet, the Visible and the Infrared during the X1 flare on 2014 March 29
• Frequently Occurring Reconnection Jets from Sunspot Light Bridges
• Light Bridge in a Developing Active Region. I. Observation of Light Bridge and its Dynamic Activity Phenomena
• 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
• On-disk coronal rain
• Fan-shaped jets above the light bridge of a sunspot driven by reconnection
• The signature of chromospheric heating in Ca II H spectra
• Formation Process of a Light Bridge Revealed with the Hinode Solar Optical Telescope
• Supersonic Downflows in a Sunspot Light Bridge
• Small-scale chromospheric jets above a sunspot light bridge
• Upflows in the central dark lane of sunspot light bridges
• Vertical Propagation of Acoustic Waves in the Solar Inter-Network as Observed by IRIS
• The energy of waves in the photosphere and lower chromosphere: 1. Velocity statistics
• The Lightweaver Framework for NLTE Radiative Transfer in Python
• Analysis of a Fragmenting Sunspot using Hinode Observations
• A Steady-state Supersonic Downflow in the Transition Region above a Sunspot Umbra
• The energy of waves in the photosphere and lower chromosphere: IV. Inversion results of Ca II H spectra
• Observational study of chromospheric heating by acoustic waves
• Heating of the solar chromosphere in a sunspot light bridge by electric currents
• Thermodynamic fluctuations in solar photospheric three-dimensional convection simulations and observations
• Narrow-Band Imaging System for the Multi-application Solar Telescope at Udaipur Solar Observatory: Characterization of Lithium Niobate Etalons
• Effects of Cowling Resistivity in the Weakly-Ionized Chromosphere
• 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)