Heating of the solar atmosphere by electric currents
Abstract
We present direct evidence of Ohmic dissipation of electric currents that leads to heating of the solar chromosphere above a light bridge in a sunspot by combining high-resolution spectroscopic Ca II IR data from the Dunn Solar Telescope with vector magnetic field observations from HMI. An extrapolation of the photospheric magnetic field from HMI to the corona using a non-force-free field technique provided the three-dimensional distribution of electric currents at locations of magnetic discontinuities, while the inversion of the chromospheric Ca II IR line spectra with the CAISAR code delivered the temperature stratifications from the photosphere to the chromosphere. The comparison of these results clearly shows that the light bridge is a site of strong electric currents of about 0.3 A m2 at the bottom boundary, which extend to about 0.7 Mm while decreasing monotonically with height. The dissipation of these currents produces a chromospheric temperature excess of about 600800 K relative to the umbra. Only the light bridge, where relatively weak and highly inclined magnetic fields emerge over a duration of 13 hrs, shows a spatial coincidence of thermal enhancements and electric currents. The temperature enhancements and the Cowling heating are primarily confined to a height range of 0.40.7 Mm above the light bridge. The corresponding increase in internal energy of 200 J m3 can be supplied by the heating in about 10 min. This heating process by Ohmic dissipation can happen at any place in the solar atmosphere where large electric currents co-exist with non-zero resistivity. Large-scale corona loops embedded in a more vertical background magnetic field could experience the same effect leading to a localized heating of coronal plasma.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2021
- Bibcode:
- 2021AGUFMSH12B..07C