A Cancellation Nanoflare Model for Solar Chromospheric and Coronal Heating. II. 2D Theory and Simulations

Syntelis, P.; Priest, E. R.; Chitta, L. P.

doi:10.3847/1538-4357/aafaf8

Cited by 46 publications

(62 citation statements)

References 68 publications

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“…The WLF occurred synchronously to this flux cancellation process. The spatial-temporal correlation between flux cancellation and this WLF strongly suggests that this WLF is powered by magnetic reconnection in the lower solar atmosphere (e.g., Syntelis et al 2019). The two small sunspots disappeared about half an hour after the white-light enhancement, likely resulted from a reconfiguration of the magnetic field structure due to the reconnection.…”

Section: Resultsmentioning

confidence: 97%

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A White-light Flare Powered by Magnetic Reconnection in the Lower Solar Atmosphere

Song

Zhu

Chen

et al. 2020

ApJL

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White-light flares (WLFs), first observed in 1859, refer to a type of solar flares showing an obvious enhancement of the visible continuum emission. This type of enhancement often occurs in most energetic flares, and is usually interpreted as a consequence of efficient heating in the lower solar atmosphere through non-thermal electrons propagating downward from the energy release site in the corona. However, this coronal-reconnection model has difficulty in explaining the recently discovered small WLFs. Here we report a C2.3 white-light flare, which are associated with several observational phenomena: fast decrease in opposite-polarity photospheric magnetic fluxes, disappearance of two adjacent pores, significant heating of the lower chromosphere, negligible increase of hard X-ray flux, and an associated U-shaped magnetic field configuration. All these suggest that this white-light flare is powered by magnetic reconnection in the lower part of the solar atmosphere rather than by reconnection higher up in the corona.

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Section: Resultsmentioning

confidence: 97%

“…It is worth mentioning that one side of a U-shaped structure may reconnect with the surrounding magnetic field during flux emergence (e.g., Syntelis et al 2019;Chen et al 2019a). In principle this process could produce a flare.…”

Section: Resultsmentioning

confidence: 99%

A White-light Flare Powered by Magnetic Reconnection in the Lower Solar Atmosphere

Song

Zhu

Chen

et al. 2020

ApJL

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“…It may be possible to generate temperatures as high as 25 kK through reconnection in the upper photosphere or lower chromosphere, as shown by Ni et al (2016Ni et al ( , 2018. Priest et al (2018) and Syntelis et al (2019) pointed out in a theoretical work that flux cancellation can cause simultaneous reconnection at different heights in the solar atmosphere. Hansteen et al (2017) found that both EBs and UV bursts were generated in a model where a flux sheet was injected some 2.5 Mm below the photosphere and allowed to emerge through the photosphere into an essentially magnetic field free corona.…”

Section: Introductionmentioning

confidence: 99%

Ellerman bombs and UV bursts: transient events in chromospheric current sheets

Hansteen

Ortiz

Archontis

et al. 2019

A&A

119

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Context. Ellerman bombs (EBs), observed in the photospheric wings of the Hα line, and UV bursts, observed in the transition region Si iv line, are both brightenings related to flux emergence regions and specifically to magnetic flux of opposite polarity that meet in the photosphere. These two reconnection-related phenomena, nominally formed far apart, occasionally occur in the same location and at the same time, thus challenging our understanding of reconnection and heating of the lower solar atmosphere. Aims. We consider the formation of an active region, including long fibrils and hot and dense coronal plasma. The emergence of a untwisted magnetic flux sheet, injected 2.5 Mm below the photosphere, is studied as it pierces the photosphere and interacts with the preexisting ambient field. Specifically, we aim to study whether EBs and UV bursts are generated as a result of such flux emergence and examine their physical relationship. Methods. The Bifrost radiative magnetohydrodynamics code was used to model flux emerging into a model atmosphere that contained a fairly strong ambient field, constraining the emerging field to a limited volume wherein multiple reconnection events occur as the field breaks through the photosphere and expands into the outer atmosphere. Synthetic spectra of the different reconnection events were computed using the 1.5D RH code and the fully 3D MULTI3D code. Results. The formation of UV bursts and EBs at intensities and with line profiles that are highly reminiscent of observed spectra are understood to be a result of the reconnection of emerging flux with itself in a long-lasting current sheet that extends over several scale heights through the chromosphere. Synthetic spectra in the Hα and Si iv 139.376 nm lines both show characteristics that are typical of the observations. These synthetic diagnostics suggest that there are no compelling reasons to assume that UV bursts occur in the photosphere. Instead, EBs and UV bursts are occasionally formed at opposite ends of a long current sheet that resides in an extended bubble of cool gas.

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“…In line with the scenario of footpoint heating, photospheric observations at the base of some active region coronal loops highlight the presence of mixed-polarity magnetic field patches that exhibit flux cancellation, a process through which energy can be supplied to heat the overlying corona (e.g., Chitta et al 2017aChitta et al , 2018. Two-dimensional (2D) and 3D magnetic reconnection models predict that such magnetic flux cancellation events at the solar surface, which would of course be associated with prior flux emergence, would trans-port energy to the loops in the upper solar atmosphere (Priest et al 2018;Syntelis et al 2019).…”

Section: Introductionmentioning

confidence: 99%

Energetics of magnetic transients in a solar active region plage

Chitta

Voort

et al. 2019

A&A

Self Cite

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Context. Densely packed coronal loops are rooted in photospheric plages in the vicinity of active regions on the Sun. The photospheric magnetic features underlying these plage areas are patches of mostly unidirectional magnetic field extending several arcsec on the solar surface. Aims. We aim to explore the transient nature of the magnetic field, its mixed-polarity characteristics, and the associated energetics in the active region plage using high spatial resolution observations and numerical simulations. Methods. We used photospheric Fe i 6173 Å spectropolarimetric observations of a decaying active region obtained from the Swedish 1-m Solar Telescope (SST). These data were inverted to retrieve the photospheric magnetic field underlying the plage as identified in the extreme-ultraviolet emission maps obtained from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). To obtain better insight into the evolution of extended unidirectional magnetic field patches on the Sun, we performed 3D radiation magnetohydrodynamic simulations of magnetoconvection using the MURaM code. Results. The observations show transient magnetic flux emergence and cancellation events within the extended predominantly unipolar patch on timescales of a few 100 s and on spatial scales comparable to granules. These transient events occur at the footpoints of active region plage loops. In one case the coronal response at the footpoints of these loops is clearly associated with the underlying transient. The numerical simulations also reveal similar magnetic flux emergence and cancellation events that extend to even smaller spatial and temporal scales. Individual simulated transient events transfer an energy flux in excess of 1 MW m −2 through the photosphere.Conclusions. We suggest that the magnetic transients could play an important role in the energetics of active region plage. Both in observations and simulations, the opposite-polarity magnetic field brought up by transient flux emergence cancels with the surrounding plage field. Magnetic reconnection associated with such transient events likely conduits magnetic energy to power the overlying chromosphere and coronal loops.

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A Cancellation Nanoflare Model for Solar Chromospheric and Coronal Heating. II. 2D Theory and Simulations

Cited by 46 publications

References 68 publications

A White-light Flare Powered by Magnetic Reconnection in the Lower Solar Atmosphere

A White-light Flare Powered by Magnetic Reconnection in the Lower Solar Atmosphere

Ellerman bombs and UV bursts: transient events in chromospheric current sheets

Energetics of magnetic transients in a solar active region plage

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