ST Distinguished Lecture | 01 August (Tue) 08:15 AM – 10:00 AM | Level 3 MR309

Diagnosis of the Coronal Magnetic Field Based on Imaging Observations

Abstract: Coronal magnetic field plays a vital role in solar eruptions, such as solar flares and coronal mass ejections (CMEs). Despite its importance, our knowledge on the coronal magnetic field is scarce since it cannot be measured directly owing to its low magnitude and the transparency of the corona. In the solar atmosphere, only the magnetic field at the solar surface can be accurately measured. Traditionally, the coronal magnetic field is extrapolated from the magnetic field on the solar surface based on some force-free models. This method is problematic in dealing with magnetic discontinuities, which are crucial for the pre-eruption magnetic structures. Several indirect methods have been developed in the past decades, one of them is based on the morphology of solar filaments.

Solar filaments are also called solar prominences when they are above the solar limb. They are cold and dense plasmas suspended in the hot and tenuous corona. They are supported by either strongly sheared or twisted coronal magnetic field, which are often the source of solar eruptions. Therefore, solar filaments are one of the perfect tracers of the coronal magnetic field structure vulnerable for eruptions. Through the efforts in the past decades, it has been found that the fine structures of solar filaments can disclose several important properties of the coronal magnetic field: (1) Once erupting, part of the filament materials would fall down to the solar surface at the two footpoints, forming conjugate brightenings. The skew of the two brightenings tells whether the magnetic field has positive or negative helicity; (2) A solar filament has several barbs, which are like the exits of highways. The orientation of these barbs can tell whether the hosting magnetic field is a flux rope or sheared arcade. (3) The fine structures of solar filaments can tell whether the hosting magnetic field is weakly or strongly twisted. (4) The period of the filament oscillations can tell the strength and the curvature radius of the supporting magnetic field. In this lecture I will introduce all these methods and their applications to the real observations.