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| Titel |
Joule heating and anomalous resistivity in the solar corona |
| VerfasserIn |
S. R. Spangler |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1023-5809
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| Digitales Dokument |
URL |
| Erschienen |
In: Nonlinear Processes in Geophysics ; 16, no. 3 ; Nr. 16, no. 3 (2009-06-30), S.443-452 |
| Datensatznummer |
250013194
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| Publikation (Nr.) |
 copernicus.org/npg-16-443-2009.pdf |
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| Zusammenfassung |
| Recent radioastronomical observations of Faraday rotation in the solar corona
can be interpreted as evidence for coronal currents, with values as large as
2.5×109 Amperes (Spangler, 2007). These estimates of currents are
used to develop a model for Joule heating in the corona. It is assumed that
the currents are concentrated in thin current sheets, as suggested by
theories of two dimensional magnetohydrodynamic turbulence. The Spitzer
result for the resistivity is adopted as a lower limit to the true
resistivity. The calculated volumetric heating rate is compared with an
independent theoretical estimate by Cranmer et al. (2007). This latter estimate
accounts for the dynamic and thermodynamic properties of the corona at a
heliocentric distance of several solar radii. Our calculated Joule heating
rate is less than the Cranmer et al estimate by at least a factor of 3×105.
The currents inferred from the observations of
Spangler (2007) are not relevant to coronal heating unless the true
resistivity is enormously increased relative to the Spitzer value. However,
the same model for turbulent current sheets used to calculate the heating
rate also gives an electron drift speed which can be comparable to the
electron thermal speed, and larger than the ion acoustic speed. It is
therefore possible that the coronal current sheets are unstable to
current-driven instabilities which produce high levels of waves, enhance the
resistivity and thus the heating rate. |
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