The loops are rooted in purely positive-polarity plage according to the magnetograms in the rightmost column. 2.1 NOAA 12443: 2015 November 5Īs our first illustrative example, Figure 1 shows an evolving collection of AR loops inside NOAA 12243, as they appear in the 17.1- and 19.3-nm passbands late on 2015 November 5. The AIA and HMI images were coaligned using the IDL procedures read_sdo and aia_prep from the SolarSoft library. For this study, we employ AIA images taken in three passbands: 17.1 nm, dominated by Fe ix ( \(T\approx 0.7\) – 0.8 MK), 19.3 nm, dominated by Fe xii ( \(T\approx 1.5\) – 1.6 MK), and 21.1 nm, dominated by Fe xiv ( \(T\approx 1.9\) – 2.0 MK). HMI provides line-of-sight magnetograms every 45 s, with a noise level of ≈10 G (Schou et al., 2012 Couvidat et al., 2016). 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 \(10^\) pixels and 12-s cadence, as well as in two UV channels and a white-light channel (Lemen et al., 2012). 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. 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. 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. 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).
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