Chromospheric activity in sunspot light bridges

Louis, Rohan E.

doi:10.1002/asna.201612429

Cited by 4 publications

(4 citation statements)

References 27 publications

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“…If the homologous nature of the flares were the result of small-scale loops emerging in the LB and reconnecting with the overlying umbral field (Tian et al 2018), one would expect blue-shifts either in localized patches or along the body of the LB (Louis et al 2020). With HMI's native spatial resolution of ∼320 km, we do not find evidence for opposite-polarity fields above uncertainties within the LB, though we do not exclude the possibility of smallscale velocity and magnetic inhomogeneities having been present (Louis et al 2009(Louis et al , 2015aLouis 2015).…”

Section: Discussioncontrasting

confidence: 65%

“…The small-scale jets originating from LBs reported so far exhibited characteristic plasma temperatures below 0.1 MK (Robustini et al 2016;Tian et al 2018) and the general notion is that the jets occur as a result of magnetic reconnection between the overlying umbral field with either emerging bipoles in the LB or with the twisted flux tube comprising the LB (Shimizu et al 2009). However this is at odds with most spectropolarimetric observations with exceptions as seen in Louis (2015). Louis et al (2015a) reported the emergence of a small-scale, flat Ω-loop in a LB.…”

Section: Introductionmentioning

confidence: 91%

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Homologous flaring activity over a sunspot light bridge in an emerging active region

Louis,

Thalmann

2020

Preprint

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Sunspot light bridges are known to exhibit a variety of dynamic and persistent phenomena such as surges, small-scale jets etc. in the chromosphere and transition region. While it has generally been proposed that magnetic reconnection is responsible for this small-scale dynamism, persistent flaring activity lasting several hours from the same spatial location on a sunspot light bridge, has rarely been reported. We combine observations from the Atmospheric Imaging Assembly and the Helioseismic Magnetic Imager on board the Solar Dynamics Observatory to investigate homologous flaring activity over a small sunspot light bridge in an emerging flux region. The homologous flares all produced broad, collimated jets, including a B6.4 class flare. The jets rise at a speed of about 200 km s −1 , reach projected heights of about 98 Mm, and emerge from the same spatial location for nearly 14 hrs, after which they cease completely. A non-linear force free extrapolation of the photospheric magnetic field shows a low-lying flux rope connecting the light bridge to a remote opposite-polarity network. The persistent flares occur as a result of the rapid horizontal motion of the leading sunspot that causes the relatively vertical magnetic fields in the adjacent umbra to reconnect with the low-lying flux rope in the light bridge. Our results indicate that the flaring ceases once the flux rope has lost sufficient twist through repeated reconnections.

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Section: Discussioncontrasting

confidence: 65%

Section: Introductionmentioning

confidence: 91%

Homologous flaring activity over a sunspot light bridge in an emerging active region

Louis,

Thalmann

2020

Preprint

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“…Such a stressed magnetic topology in LBs has often been cited as the driver for a number of reconnectionassociated phenomena such as small-scale jets (Louis et al 2014;Tian et al 2018), surges (Roy 1973;Asai et al 2001;Toriumi et al 2015;Robustini et al 2016), strong brightenings and/or ejections (Louis et al 2008;Shimizu et al 2009;Louis et al 2009), as well as flares (Berger & Berdyugina 2003;Louis & Thalmann 2021). Enhanced chromospheric activity, which is primarily transient in nature, appears to be an important characteristic of LBs (Louis 2016).…”

Section: Introductionmentioning

confidence: 99%

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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“…Such a stressed magnetic topology in LBs has often been cited as the driver for a number of reconnection-associated phenomena such as small-scale jets (Louis et al 2014;Tian et al 2018), surges (Roy 1973;Asai et al 2001;Toriumi et al 2015;Robustini et al 2016), strong brightenings and/or ejections (Louis et al 2008;Shimizu et al 2009;Louis et al 2009), as well as flares (Berger & Berdyugina 2003;Louis & Thalmann 2021). Enhanced chromospheric activity, which is primarily transient in nature, appears to be an important characteristic of LBs (Louis 2016).…”

Section: Introductionmentioning

confidence: 99%

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

Louis¹,

Mathew²,

Bayanna³

et al. 2023

Preprint

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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 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 Å 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 red-shifts 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 × 10 26 erg and matches the radiative losses. It could be supplied by magnetic flux loss of the sunspot (7.5 × 10 27 erg), kinetic energy from the increase in the LB width (4 × 10 28 erg), or freefall of mass along the coronal loops (6.3 × 10 26 erg).

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Chromospheric activity in sunspot light bridges

Cited by 4 publications

References 27 publications

Homologous flaring activity over a sunspot light bridge in an emerging active region

Homologous flaring activity over a sunspot light bridge in an emerging active region

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

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