The Non-Eruptive Reconfiguration of a Quiescent Filament After a Nearby Active Region Emergence

TL;DR

This study investigates why a quiescent solar filament remained stable despite nearby flux emergence from active region NOAA 13270. By integrating multi-viewpoint EUV/X-ray imaging, spectroscopy, radio observations, and NLFFF extrapolations, the authors identify a coronal null-point and a fan-spine topology that enable slow, continuous reconnection and energy transfer into the filament without triggering eruption. The persistent reconnection, coupled with jets away from the filament and a flare occurring in overlying strapping loops, relieves magnetic stress and preserves filament integrity, highlighting the role of flux orientation relative to the ambient field as a critical determinant of eruption potential. The results provide observational constraints for models of filament stability, offering a two-step reconnection picture and a cartoon framework to understand non-eruptive interactions in complex magnetic environments.

Abstract

The unpredictability of solar filament eruptions presents major challenges for forecasting space weather, as such eruptions frequently drive coronal mass ejections (CMEs) that impact the heliosphere. While nearby flux emergence is often linked to their destabilisation, the specific characteristics of both the emerging flux and the filament that determine whether an eruption occurs remain unclear. We report observations of a quiescent filament that did not erupt following the nearby emergence of active region NOAA 13270 and a subsequent C-class flare in April 2023. Our analysis combines multi-viewpoint extreme ultraviolet (EUV) imaging and X-ray imaging with EUV spectroscopy, radio imaging and measurements of, and extrapolations from, the photospheric magnetic field. We identify the formation of a coronal null point and fan-spine topology at the interface between the active region and filament which exhibited persistent slow reconnection, indicated by chromospheric brightenings, persistent radio emission, and plasma upflows. Our results indicate that ongoing reconnection and jets can relieve magnetic stress and enable filament stability, even when under strong perturbation. We suggest that the orientation of emerging flux relative to the ambient field is a critical parameter in filament evolution, and provide observational constraints for models of filament stability and eruption.

Figures (10)

• Figure 1: The positions of Solar Orbiter and Earth, viewed from above the ecliptic plane. Their locations for the period from 00:00 UT on 1 April to 00:00 UT on 7 April 2023 are highlighted in red. The active region's path on the solar surface between these times is shown in blue, and a yellow line projects radially from the centre of the active region for the dates of the study.
• Figure 2: Observations of the emergence of NOAA 13270 on 1 April (left), and the subsequent remote brightenings on 2 April (right). Coronal plasma as seen by SDO/AIA in the 193 Å channel is shown in the top row, and the line-of-sight photospheric magnetic field measured by SDO/HMI is shown in the bottom row.
• Figure 3: Observations of the expanding circular ribbon around the east side of NOAA 13270, and the movement of the filament material on 3 April, as seen in the SDO/AIA 304 Å channel. This figure is available as an animation.
• Figure 4: NLFFF extrapolation of the photospheric vector magnetic field measured by SDO/HMI on 3 April. The flux rope at the core of the filament channel is shown in blue, the overlying field in red, the null fan in yellow and the higher strapping field in green. The view point is orientated to match that of Earth.
• Figure 5: NLFFF extrapolation of the photospheric vector magnetic field measured by SDO/HMI on 4 April. The high altitude strapping field is shown in green, lower-level overlying field in orange, field originating at the new positive polarity and, via a null point forming part of a fan topology in yellow, and field originating in the new positive polarity connected via the null point to the filament channel in blue. A Qmap showing $\log{}Q$ in the y-z plane at the null point is shown, with the colours placed behind the field lines for visibility, and where brighter regions are those of high $Q$ values.