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

Abstract

AbstractDuring 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.