Understanding the magnetic field and plasma-$\beta$ along umbral fan loops traced using 3-min slow waves

Abstract

The plasma-$\beta$ is an important fundamental physical quantity in solar plasma physics, which determines the dominating process in the solar atmosphere, i.e., magnetic or thermodynamic processes. Here, for the first time, we provide variations of magnetic field and plasma-$\beta$ along magnetically structured loops from the photosphere to the corona. We have selected several fan loops rooted in sunspot umbra observed simultaneously by the Interface Region Imaging Spectrograph and Solar Dynamics Observatory. The 3-min slow waves enabled us to trace and analyze several fan loops with cross-sectional areas in the lower atmosphere and locate their footpoints at the photosphere. We find the RMS magnetic field strengths in the range 1596-2269 G at the photospheric footpoints of the fan loops, which decrease rapidly to 158-236 G at the coronal footpoints. We estimated the plasma-$\beta$ at the photospheric and coronal footpoints in the range 0.2-0.5 and 0.0001-0.001, respectively. We found plasma-$\beta$$<$$1$ along the whole loop, whereas the plasma-$\beta$$\approx$$1$ layer is found to be at sub-photospheric heights. We compared our findings for isolated individual fan loops with a previously established model for active regions and found an almost similar pattern in variations with height, but with different plasma-$\beta$ values. Our results demonstrate the seismological potential of 3-min slow waves omnipresent in the umbral sunspot atmosphere to probe and map isolated loops and determine magnetic field and plasma-$\beta$ along these loops. The obtained parameters provide crucial ingredients for the theoretical modeling of the umbral atmosphere and wave dynamics along loops.

arXiv commentPublished in 2025 ApJL 988 L26

References in corpus (26)

• The Interface Region Imaging Spectrograph (IRIS)
• A Critical Assessment of Nonlinear Force-Free Field Modeling of the Solar Corona for Active Region 10953
• Differential Emission Measures from the Regularized Inversion of Hinode and SDO data
• Multiwavelength studies of MHD waves in the solar chromosphere: An overview of recent results
• Global maps of the magnetic field in the solar corona
• Coronal Loop Oscillations Observed with AIA - Kink-Mode with Cross-Sectional and Density Oscillations
• Magnetic Structure of Sunspots
• Spectral Line Selection for HMI: A Comparison of Fe I 6173 and Ni I 6768
• Signatures of Alfven waves in the polar coronal holes as seen by EIS/Hinode
• Alfvén Wave Dissipation in the Solar Chromosphere
• The Influence of the Magnetic Field on Running Penumbral Waves in the Solar Chromosphere
• Solar coronal magnetic fields derived using seismology techniques applied to omnipresent sunspot waves
• Determination of the Coronal Magnetic Field by Hot Loop Oscillations
• Proton, Electron, and Ion Heating in the Fast Solar Wind from Nonlinear Coupling Between Alfvenic and Fast-Mode Turbulence
• The polytropic index of solar coronal plasma in sunspot fan loops and its temperature dependence
• A first spectroscopic measurement of the magnetic field strength for an active region of the solar corona
• Plasma Beta Stratification in the Solar Atmosphere: A Possible Explanation for the Penumbra Formation
• Spectroscopic Observations of a Coronal Loop: Basic Physical Plasma Parameters Along the Full Loop Length
• Longitudinal oscillations in density stratified and expanding solar waveguides
• Measurements of Coronal Magnetic Field Strengths in Solar Active Region Loops
• Fan Loops Observed by IRIS, EIS and AIA
• Exploring the damping of Alfvén waves along a long off-limb coronal loop, up to 1.4 R${}_{\odot }$
• An ultra-long and quite thin coronal loop without significant expansion
• Exploring source region of 3-min slow magnetoacoustic waves observed in coronal fan loops rooted in sunspot umbra
• Spectroscopic and imaging observations of transient hot and cool loops by IRIS and SDO
• Kelvin-Helmholtz instability and heating in oscillating loops perturbed by power-law transverse wave drivers