Magnetic Separatrix as the Source Region of the Plasma Supply for an Active-region Filament

Abstract

Solar filaments can be formed via chromospheric evaporation followed by condensation in the corona or by the direct injection of cool plasma from the chromosphere to the corona. In this paper, with high-resolution Hα data observed by the 1.6 m New Solar Telescope of the Big Bear Solar Observatory on 2015 August 21, we confirmed that an active-region filament is maintained by the continuous injection of cold chromospheric plasma. We find that the filament is rooted along a bright ridge in Hα, which corresponds to the intersection of a magnetic quasiseparatrix layer with the solar surface. This bright ridge consists of many small patches and the sizes of these patches are comparable to the width of the filament threads. It is found that upflows originate from the brighter patches of the ridge, whereas the downflows move toward the weaker patches of the ridge. The whole filament is composed of two opposite directional streams, implying that longitudinal oscillations are not the only cause of the counterstreamings, and unidirectional siphon flows with alternative directions are another possibility.

Formation and material supply of an active-region filament associated with newly emerging flux

“…Furthermore, the only few observation evidences could be captured to supported to the this models (Berger et al 2012;. On the other hand, many observations are more likely to support the injection models which rely on magnetic reconnection in the low atmosphere to propel cool plasma to typical filament height (Wang 1999;Liu et al 2005;Zou et al 2017;Wang et al 2018). In this paper, we supplied a observational evidence that the filament material can be supplied by a series of jets related to the new emerging magnetic field, which again verify the injection model.…”

Damping Mechanisms of the Solar Filament Longitudinal Oscillations in the Weak Magnetic Field

“…Filament longitudinal oscillations were first reported by Jing et al (2003), and in fact, the counterstreamings existing in many solar filaments might be due to longitudinal oscillations of filament threads (Lin et al 2003), although the counterstreamings in some filaments are alternating unidirectional flows (Zou et al 2017) or are the combination of filament thread longitudinal oscillations and unidirectional flows . Several mechanisms were put forward to account for the restoring force of the filament longitudinal oscillations, such as the magnetic field-aligned component of gravity, gas pressure, and magnetic tension force (Jing et al 2003;Vršnak et al 2007).…”

Formation and Characteristics of Filament Threads in Double-Dipped Magnetic Flux Tubes

“…Filaments are generally formed along filament channels, which follow along the polarity inversion line (PIL). While magnetic dips may not be necessary in some filaments where continuous formation and drainage of cold threads maintain the dynamic appearance of filaments (Karpen et al 2001;Zou et al 2016Zou et al , 2017, it is believed that most filaments are supported against gravity by the Lorentz force in magnetic dips, where the cold plasma is trapped. Generally, magnetic structures with dips can be described by two idealized models: sheared arcades (Kippenhahn & Schlüter 1957;Antiochos et al 1994), and magnetic flux ropes (Kuperus & Raadu 1974).…”