The dependence of the magnetism of a near-limb sunspot on height

Abstract

The physical parameters of the sunspot are not fully understood, especially the height dependence of the magnetic field. So far, it is also an open question as to which heights the He I 1083 nm spectral line is formed at. Our aim is to investigate the magnetic and dynamical properties in the atmosphere above a sunspot, from the photosphere to the chromosphere. We analyzed the photospheric and chromospheric magnetic field properties of a stable sunspot in AR 12553 on June 20, 2016 using spectropolarimetric observations obtained with GRIS at GREGOR. A spectral-line inversion technique was used to infer the magnetic field vector and Doppler velocities from the full Stokes profiles. In total, three spectral lines were inverted and the variation of the magnetic properties was qualified using the average values of the radial circles. The sunspot is located close to the solar limb, and thus this allows us to make a geometrical determination of the height of the spectral line He I 1083 nm. We find the height of helium spectral line to be 970 km above the photospheric spectral lines directly from observation at a stable sunspot. The total magnetic field strength decreases with height over the sunspot; the rates are -0.34 G/km for the umbra and -0.28 G/km for the penumbra. The inclination increases with increasing height in the umbra, but decreases in the penumbra. In the umbra, the vertical component ($B_z$) decreases with height, while the horizontal component ($B_{hor}$) remains almost constant. In the penumbra this is reversed, as $B_z$ remains nearly constant over height, while $B_{hor}$ decreases. We also observe fast velocities with 30 km/s in small chromospheric patches on the central side of the spot. The key parameters depending on height in the sunspot are the $B_z$ component of the magnetic field for the umbra and the $B_{hor}$ component of the magnetic field for the penumbra.

Accepted for publication in Astronomy & Astrophysics, 11 pages, 9 figures

References in corpus (16)

• An Open Source, Massively Parallel Code for Non-LTE Synthesis and Inversion of Spectral Lines and Zeeman-induced Stokes Profiles
• Advanced Forward Modeling and Inversion of Stokes Profiles Resulting from the Joint Action of the Hanle and Zeeman Effects
• Critical Science Plan for the Daniel K. Inouye Solar Telescope (DKIST)
• The European Solar Telescope
• Recovering Thermodynamics from Spectral Profiles observed by IRIS: A Machine and Deep Learning Approach
• Spectropolarimetric observations of the Ca II 8498 A and 8542 A lines in the quiet Sun
• Spectropolarimetric analysis of an active region filament. I. Magnetic and dynamical properties from single component inversions
• Determining the dynamics and magnetic fields in He I 10830 Å during a solar filament eruption
• Upper Chromospheric Magnetic Field of a Sunspot Penumbra: Observations of Fine Structure
• Vertical magnetic field gradient in the photospheric layers of sunspots
• Three-dimensional magnetic field structure of a flux emerging region in the solar atmosphere
• The Height of Chromospheric Loops in an Emerging Flux Region
• The role of the chromospheric magnetic canopy in the formation of a sunspot penumbra
• Magnetized supersonic downflows in the chromosphere. A statistical study using the He I 10830 Å lines
• Magnetic field fluctuations in the shocked umbral chromosphere
• Tracking downflows from the chromosphere to the photosphere in a solar arch filament system