The magnetic topology of the inverse Evershed flow

Prasad, A.; Ranganathan, Mohanakrishna; Beck, C.; Choudhary, Debi Prasad; Hu, Qiang

doi:10.1051/0004-6361/202142585

Cited by 5 publications

(5 citation statements)

References 74 publications

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“…Furthermore, we do not unambiguously detect blueshifts at the other end of the loops, which would provide evidence for a siphon flow (Cargill & Priest 1980;Straus et al 2015;Prasad et al 2022). The LB along with the network flux region are redshifted, which raises questions on how any flow would be sustained for a period of days.…”

Section: Lb Energy Budgetmentioning

confidence: 59%

Sustained Heating of the Chromosphere and Transition Region Over a Sunspot Light Bridge

Louis

Mathew

Bayanna

et al. 2023

ApJ

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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 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 and 211 Å intensities 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 redshifts of 5–20 km s−1 with occasional supersonic downflows exceeding 100 km s−1. The excess thermal energy over the LB is about 3.2 × 1026 erg and matches the radiative losses. It could be supplied by magnetic flux loss of the sunspot (7.5 × 1027 erg), kinetic energy from the increase in the LB width (4 × 1028 erg), or freefall of mass along the coronal loops (6.3 × 1026 erg).

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Section: Lb Energy Budgetmentioning

confidence: 59%

Sustained Heating of the Chromosphere and Transition Region Over a Sunspot Light Bridge

Louis

Mathew

Bayanna

et al. 2023

ApJ

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“…Observations were taken on 2015 September 16 with the Interferometric Bidimensional Spectrometer (IBIS; Cavallini 2006) at the Dunn Solar Telescope (DST) of the decaying AR NOAA 12418. The data were utilized by Beck & Choudhary (2020) and Prasad et al (2022), where they are discussed in detail, thus only a short description is presented here. The IBIS field of view was placed over the leading sunspot of the group, located at [x, y] = [−520″, −340″] with respect to solar disk center.…”

Section: Observationsmentioning

confidence: 99%

Unveiling the True Nature of Plasma Dynamics from the Reference Frame of a Superpenumbral Fibril

Bate,

Jess,

Grant

et al. 2024

ApJ

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The magnetic geometry of the solar atmosphere, combined with projection effects, makes it difficult to accurately map the propagation of ubiquitous waves in fibrillar structures. These waves are of interest due to their ability to carry energy into the chromosphere and deposit it through damping and dissipation mechanisms. To this end, the Interferometric Bidimensional Spectrometer at the Dunn Solar Telescope was employed to capture high-resolution Hα spectral scans of a sunspot, with the transverse oscillations of a prominent superpenumbral fibril examined in depth. The oscillations are reprojected from the helioprojective Cartesian frame to a new frame of reference oriented along the average fibril axis through nonlinear force-free field extrapolations. The fibril was found to be carrying an elliptically polarized, propagating kink oscillation with a period of 430 s and a phase velocity of 69 ± 4 km s−1. The oscillation is damped as it propagates away from the sunspot with a damping length of approximately 9.2 Mm, resulting in the energy flux decreasing at a rate on the order of 460 W m−2/Mm. The Hα line width is examined and found to increase with distance from the sunspot, a potential sign of a temperature increase. Different linear and nonlinear mechanisms are investigated for the damping of the wave energy flux, but a first-order approximation of their combined effects is insufficient to recreate the observed damping length by a factor of at least 3. It is anticipated that the reprojection methodology demonstrated in this study will aid with future studies of transverse waves within fibrillar structures.

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“…The flow could be directed from the foot point of a flux tube with weaker magnetic field strength. Following the procedures in Prasad et al (2022), we tested this hypothesis by comparing the field strength of the field line foot points in a nonlinear force-free field extrapolation model (Wiegelmann et al 2012). Unfortunately, the result is inconclusive.…”

Section: On the Origin Of A Large Photospheric Doppler Shiftmentioning

confidence: 99%

Large Photospheric Doppler Shift in Solar Active Region 12673. I. Field-aligned Flows

Liu 刘,

Sun 孙,

Schuck

et al. 2023

ApJ

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Delta (δ) sunspots sometimes host fast photospheric flows along the central magnetic polarity inversion line (PIL). Here we study the strong Doppler shift signature in the central penumbral light bridge of solar active region NOAA 12673. Observations from the Helioseismic and Magnetic Imager (HMI) indicate highly sheared and strong magnetic fields. Large Doppler shifts up to 3.2 km s−1 appeared during the formation of the light bridge and persisted for about 16 hr. A new velocity estimator, called DAVE4VMwDV, reveals fast converging and shearing motion along the PIL from HMI vector magnetograms, and recovers the observed Doppler signal much better than an old version of the algorithm. The inferred velocity vectors are largely (anti-)parallel to the inclined magnetic fields, suggesting that the observed Doppler shift contains a significant contribution from the projected field-aligned flows. High-resolution observations from the Hinode/Spectro-Polarimeter further exhibit a clear correlation between the Doppler velocity and the cosine of the magnetic inclination, which is in agreement with HMI results and consistent with a field-aligned flow of about 9.6 km s−1. The complex Stokes profiles suggest significant gradients of physical variables along the line of sight. We discuss the implications on the δ-spot magnetic structure and the flow-driving mechanism.

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The magnetic topology of the inverse Evershed flow

Cited by 5 publications

References 74 publications

Sustained Heating of the Chromosphere and Transition Region Over a Sunspot Light Bridge

Sustained Heating of the Chromosphere and Transition Region Over a Sunspot Light Bridge

Unveiling the True Nature of Plasma Dynamics from the Reference Frame of a Superpenumbral Fibril

Large Photospheric Doppler Shift in Solar Active Region 12673. I. Field-aligned Flows

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