Measurements of Photospheric and Chromospheric Magnetic Field Structures Associated with Chromospheric Heating over a Solar Plage Region

Anan, Tetsu; Schad, Thomas A.; Kitai, Reizaburo; Dima, Gabriel I.; Jaeggli, Sarah A.; Tarr, Lucas A.; Collados, M.; Domínguez-Tagle, Carlos; Kleint, Lucia

doi:10.3847/1538-4357/ac1b9c

Cited by 26 publications

(26 citation statements)

References 141 publications

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“…Our results are somewhat different than those reported by Anan et al (2021), but surprisingly also compatible. Their observations were based on arguably lower spatial-resolution slitspectrograph raster scans in the Mg ii h&k lines (IRIS) and in the He i 10830 Å line.…”

Section: Discussioncontrasting

confidence: 95%

“…The exact set of processes that are at work in plage and their contribution to the energy budget remains highly unconstrained from observations. A great discussion and exhaustive review about the potential contribution of different heating mechanisms in plage is presented by Anan et al (2021). They also analyzed the correlations of the radiative flux in the Mg ii h&k lines and with the magnetic field strength that was inferred from observations in the He i 10830 Å line.…”

Section: Introductionmentioning

confidence: 99%

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Spatio-temporal analysis of chromospheric heating in a plage region

Morosin,

Rodríguez,

Baso

et al. 2022

Preprint

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Context. Our knowledge of the heating mechanisms that are at work in the chromosphere of plage regions remains highly unconstrained from observational studies. While many heating candidates have been proposed in theoretical studies, the exact contribution from each of them is still unknown. The problem is rather difficult because there is not direct way of estimating the heating terms from chromospheric observations. Aims. The purpose of our study is to estimate the chromospheric heating terms from a multi-line high spatial-resolution plage dataset, characterize their spatio-temporal distribution and set constraints on the heating processes that are at work in the chromosphere. Methods. We make use of non-local thermodynamical equilibrium (NLTE) inversions in order to infer a model of the photosphere and chromosphere of a plage dataset acquired with the Swedish 1-m Solar Telescope (SST). We use this model atmosphere to calculate the chromospheric radiative losses from the main chromospheric cooler from H i, Ca ii and Mg ii atoms. In this study, we approximate the chromospheric heating terms by the net radiative losses predicted by the inverted model. In order to make the analysis of timeseries over a large field-of-view (FOV) computationally tractable, we make use of a neural network which is trained from the inverted models of two non-consecutive time-steps. We have divided the chromosphere in three regions (lower, middle, upper) and analyzed how the distribution of the radiative losses is correlated with the physical parameters of the model. Results. In the lower chromosphere, the contribution from the Ca ii lines is dominant and predominantly located in the surroundings of the photospheric footpoints. In the upper chromosphere, the H i contribution is dominant. Radiative losses in the upper chromosphere form a relatively homogeneous patch that covers the entire plage region. The Mg ii also peaks in the upper chromosphere. Our time analysis shows that in all pixels, the net radiative losses can be split in a periodic component with an average amplitude of amp Q = 7.6 kW m −2 and a static (or very slowly evolving) component with a mean value of -26.1 kW m −2 . The period of the modulation present in the net radiative losses matches that of the line-of-sight velocity of the model. Conclusions. Our interpretation is that in the lower chromosphere, the radiative losses are tracing the sharp lower edge of the hot magnetic canopy that is formed above the photosphere, where the electric current is expected to be large. Therefore Ohmic current dissipation could explain the observed distribution. In the upper chromosphere, both the magnetic field and the distribution of net radiative losses are room-filling and relatively smooth, whereas the amplitude of the periodic component is largest. Our results suggest that acoustic wave heating may be responsible for one third of the energy deposition in the upper chromosphere, whereas other heating mechanisms must be responsible for the rest: turbulent Alfvén wave dissipation or...

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Section: Discussioncontrasting

confidence: 95%

Section: Introductionmentioning

confidence: 99%

Spatio-temporal analysis of chromospheric heating in a plage region

Morosin,

Rodríguez,

Baso

et al. 2022

Preprint

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“…Although we have been concerned here only with the heating of the corona, it may be that mixed-polarity flux on even smaller scales plays an important part in chromospheric heating, given the power law distribution of flux emergence. In their high-resolution spectropolarimetric study of chromospheric heating in a plage region, Anan et al (2021) found that the Mg II radiative flux (a measure of the heating rate) was highest in between or at the edges of the individual strong field patches within the plage, and was poorly correlated with the local chromospheric or photospheric field strength. Reconnection with small bipoles scattered through the plage might account for such off-center heating.…”

Section: Summary and Discussionmentioning

confidence: 99%

“…Similarly, Aschwanden et al (2007) mentioned as a "caveat" against the chromospheric evaporation scenario "the nondetection of the initial heating agent (small-scale reconnection events in the transition region)". More recently, in their observational study of the relation between magnetic structures and signatures of heating in a plage region, Anan et al (2021) found that the fraction of opposite-polarity fields was too small to support reconnection mechanisms, except possibly in the "strong guide-field regime." However, we have recently come to question the reliability of present-day magnetograms in detecting minority-polarity flux in the presence of a strongly dominant polarity.…”

Section: Introductionmentioning

confidence: 99%

“…loops. According to recent spectropolarimetric analyses of plage regions byMorosin et al (2020),Pietrow et al (2020), andAnan et al (2021), the strength of the longitudinal field component in the chromosphere (at heights of up to ∼1 Mm, where the canopy has fully formed) is typically on the order of 400 G. Assuming that the field strength at the coronal base, B 0 , is comparable to that in the upper chromosphere, we therefore normalize our estimates to B 0 ∼ 400 G. The recycling time or timescale for an equal amount of minority-polarity flux to emerge under the plage field is given by…”

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confidence: 99%

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Undetected Minority-polarity Flux as the Missing Link in Coronal Heating

Wang¹

2022

Preprint

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During the last few decades, the most widely favored models for coronal heating have involved the in situ dissipation of energy, with footpoint shuffling giving rise to multiple current sheets (the “nanoflare” model) or to Alfv´en waves that leak into the corona and undergo dissipative interactions (the wave heating scenario). As has been recognized earlier, observations suggest instead that the energy deposition is concentrated at very low heights, with the coronal loops being filled with hot, dense material from below, which accounts for their overdensities and flat temperature profiles. While an obvious mechanism for footpoint heating would be reconnection with small-scale fields, this possibility seems to have been widely ignored because magnetograms show almost no minority-polarity flux inside active region (AR) plages. Here, we present further examples to support our earlier conclusions (1) that magnetograms greatly underrepresent the amount of minority-polarity flux inside plages and “unipolar” network, and (2) that small loops are a major constituent of Fe IX 17.1 nm moss. On the assumption that the emergence or churning rate of small-scale flux is the same inside plages as in mixed-polarity regions of the quiet Sun, we estimate the energy flux density associated with reconnection with the plage fields to be on the order of 107 erg cm−2 s −1 , sufficient to heat the AR corona.

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Undetected Minority-Polarity Flux as the Missing Link in Coronal Heating

Wang

2022

Sol Phys

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During the last few decades, the most widely favored models for coronal heating have involved the in situ dissipation of energy, with footpoint shuffling giving rise to multiple current sheets (the nanoflare model) or to Alfvén waves that leak into the corona and undergo dissipative interactions (the wave heating scenario). As has been recognized earlier, observations suggest instead that the energy deposition is concentrated at low heights, with the coronal loops being filled with hot, dense material from below, which accounts for their overdensities and flat temperature profiles. While an obvious mechanism for footpoint heating would be reconnection with small-scale fields, this possibility seems to have been widely ignored because magnetograms show almost no minority-polarity flux inside active-region (AR) plages. Here, we present further examples to support our earlier conclusions (1) that magnetograms greatly underrepresent the amount of minority-polarity flux inside plages and “unipolar” network, and (2) that small loops are a major constituent of Fe ix 17.1-nm moss. On the assumption that the emergence or churning rate of small-scale flux is the same inside plages as in mixed-polarity regions of the quiet Sun, we estimate the energy flux density associated with reconnection with the plage fields to be on the order of $10^{7}~\mbox{erg}\,\mbox{cm}^{-2}\,\mbox{s}^{-1}$ 10 7 erg cm − 2 s − 1 , sufficient to heat the AR corona.

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Measurements of Photospheric and Chromospheric Magnetic Field Structures Associated with Chromospheric Heating over a Solar Plage Region

Cited by 26 publications

References 141 publications

Spatio-temporal analysis of chromospheric heating in a plage region

Spatio-temporal analysis of chromospheric heating in a plage region

Undetected Minority-polarity Flux as the Missing Link in Coronal Heating

Undetected Minority-Polarity Flux as the Missing Link in Coronal Heating

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