Filament Shape Versus Coronal Potential Magnetic Field Structure

TL;DR

This study links filament shapes to coronal magnetic field structures by comparing observed filament material with calculated polarity inversion lines at different heights, enabling filament height estimation and understanding of filament morphology.

Contribution

It introduces a method to estimate filament heights using PIL matching and explains filament morphology through potential and non-potential magnetic field analysis.

Findings

Filament material is enclosed between two PILs at different heights.

Filament spine height correlates with the height of the higher PIL.

Matching PILs with filament borders can estimate filament height.

Abstract

Solar filament shape in projection on disc depends on the structure of the coronal magnetic field. We calculate the position of polarity inversion lines (PILs) of coronal potential magnetic field at different heights above the photosphere, which compose the magnetic neutral surface, and compare with them the distribution of the filament material in H$\alpha$ chromospheric images. We found that the most of the filament material is enclosed between two polarity inversion lines (PILs), one at a lower height close to the chromosphere and one at a higher level, which can be considered as a height of the filament spine. Observations of the same filament on the limb by the {\it STEREO} spacecraft confirm that the height of the spine is really very close to the value obtained from the PIL and filament border matching. Such matching can be used for filament height estimations in on-disk observations. Filament barbs are housed within protruding sections of the low-level PIL. On the base of simple model, we show that the similarity of the neutral surfaces in potential and non-potential fields with the same sub-photospheric sources is the reason for the found tendency for the filament material to gather near the potential-field neutral surface.