Solar Filament Physiognomy: Inferring Magnetic Quantities from Imaging Observations

TL;DR

This paper reviews the development of solar filament physiognomy, a method to infer coronal magnetic quantities from imaging observations, which could advance solar physics with upcoming large telescopes.

Contribution

It provides a comprehensive review of past efforts in solar filament physiognomy and discusses its potential with future high-resolution observations.

Findings

Solar filament physiognomy offers a promising way to infer coronal magnetic fields.

Recent advances in imaging technology can enhance the accuracy of this approach.

The method could complement existing techniques like extrapolation and seismology.

Abstract

Magnetic field is the key physical quantity in solar physics as it controls all kinds of solar activity, ranging from nanoflares to big flares and coronal mass ejections (CMEs). However, so far only the magnetic field on the solar surface can be more or less precisely measured, and the most important coronal magnetic field remains undetectable accurately. Without the knowledge of the coronal magnetic field, it is even more difficult to obtain secondary quantities related to magnetic field, such as the magnetic helicity and magnetic configuration, including the curvature of field lines. The prevailing approaches to obtain the coronal magnetic field include coronal magnetic extrapolation and coronal seismology. Actually there were scattered efforts to derive secondary magnetic quantities based on imaging observations of solar filaments, without the help of polarization measurements. We call this approach solar filament physiognomy. In this paper, we review these efforts made in the past decades, and point out that this approach will be promising as large telescopes are being built and more fine structures of filament channels will be revealed.