PLASMA BETA ABOVE A SOLAR ACTIVE REGION: RETHINKING THE PARADIGM


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Abstract

In this paper, we present a model of the plasma beta above an active region and discuss its consequences in terms of coronal magnetic field modeling. The β-plasma model is representative and derived from a collection of sources. The resulting β variation with height in the solar atmosphere is used to emphasize that the assumption that the magnetic pressure dominates over the plasma pressure must be carefully employed when extrapolating the magnetic field. This paper points out (1) that the paradigm that the coronal magnetic field can be constructed from a force-free magnetic field must be used in the correct context, since the force-free region is sandwiched between two regions which have β>1, (2) that the chromospheric Mg ii–C iv magnetic measurements occur near the β-minimum, and (3) that, moving from the photosphere upwards, β can return to ∼1 at relatively low coronal heights, e.g., R∼1.2 Rs.

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