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The Evolution of a Sheared Potential Magnetic Field in the Solar Corona

Published online by Cambridge University Press:  19 July 2016

J. T. Karpen
Affiliation:
Naval Research Laboratory, Washington, DC 20375-5000
S. K. Antiochos
Affiliation:
Naval Research Laboratory, Washington, DC 20375-5000
C. R. DeVore
Affiliation:
Naval Research Laboratory, Washington, DC 20375-5000

Extract

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Several theoretical studies have proposed that, in response to photospheric foot-point motions, current sheets can be generated in the solar corona without the presence of a null point in the initial potential magnetic field. In these analytic models, current sheets form wherever the coronal field dips down and is parallel to the photosphere. A fundamental assumption in these analyses — commonly referred to as the line-tying assumption — is that all coronal field lines are anchored to a boundary surface representing the top of the dense, gas-pressure-dominated photosphere. In theoretical arguments presented elsewhere (Karpen, Antiochos, and DeVore 1989), however, we show that line-tying is not valid for “dipped” coronal fields, and hence that the conclusions of the line-tied models are incorrect. We contend that current sheets will not form if the photosphere-corona interface is represented by a physically valid model. Here we summarize a numerical investigation of the response of a “dipped” potential magnetic field in a hydrostatic-equilibrium atmosphere to shearing motions of the foot points. Our results show that, in the absence of artificial line-tying conditions, a current sheet indeed does not form at the location of the dip. Rather, the dipped magnetic field rises, causing upflows of photospheric and chromospheric plasma.

Type
VII. Magnetic Reconnection and Coronal Evolution
Copyright
Copyright © Kluwer 1990 

References

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