Resolving Interchange Reconnection Dynamics in a Fan-Spine-like Topology Observed by Solar Orbiter

TL;DR

The paper uses unprecedentedly high-resolution EUV imaging from Solar Orbiter's EUI to investigate interchange reconnection around a small-scale fan-spine-like topology. It identifies three current sheets (CS1–CS3) near the null point, with CS2 and CS3 linked to filament eruptions and a curtain-like reconnection structure, and a persistent curtain outflow with a ~200 s periodicity. Reconnection rates are estimated in the ranges $0.12$–$0.20$ for CS2 and $0.12$–$0.17$ for CS3, highlighting rapid, recurrent activity modulated by emerging magnetic structures. The findings reveal self-similarity between small fan-spine systems and large-scale pseudostreamers, suggesting multiple nulls and QSLs/separators govern complex interchange reconnection and energy transfer to the high corona and heliosphere.

Abstract

Interchange reconnection is believed to play a significant role in the production of solar jets and solar wind. However, the dynamics of interchange reconnection in the low corona might be more complex than recognized before in higher temporal and spatial resolutions. Using unprecedentedly high-resolution observations from the Extreme Ultraviolet Imager (EUI) onboard the Solar Orbiter, we analyze the dynamics of interchange reconnection in a small-scale fan-spine-like topology. Interchange reconnection that continuously occurs around the multi-null points of the fan-spine-like system exhibits a quasi-periodicity of ~200 s, nearly covering the entire evolution of this system. Continuous evolution and reversal of multiple current sheets are observed over time near the null point. These results reveal that the dynamics of interchange reconnection are likely modulated by the emerging magnetic structures, such as mini-filaments and emerging arcades. Moreover, a curtain-like feature with a width of 1.7 Mm is also observed near the interchange reconnection region and persistently generates outflows, which is similar to the separatrix curtain reported in the pseudo-streamer structure. This study not only demonstrates the complex and variable reconnection dynamics of interchange reconnection within small-scale fan-spine topology but also provides insights into the self-similarity of magnetic field configurations across multiple temporal and spatial scales.

Figures (7)

• Figure 1: a: Positions of Solar Orbiter and Earth at 22:20 UT on 2024 April 5. The HRIEUV inverted grayscale is overlaid on the FSI$_{174}$ image. It shows the location of a fan-spine-like structure at this time. The field of view in panel (b) corresponds to the red box indicated in panel (a), showing the HRI overlaid on the FSI image at 22:20 UT c: Zoom-in of HRIEUV 174 Å ( cyan box in b) showing the structure at the solar limb at a scale of about 15 Mm.
• Figure 2: (a)$-$(e): HRIEUV 174Å sequence images depicting the evolution process of the fan-spine-like topology. In panel (b), the emerged and ambient open field are outlined by dashed green and white lines, respectively. The yellow arrows point to the X point of reconnection between the emerging field and the surrounding open magnetic field in panel (c). The pink arrows denote the plasma blobs in current sheet 1 (d). Panel (e): Fan surface and spine of the fan-spine-like structure are outlined by dashed red lines, and the dashed green and white lines outline the closed magnetic flux under the fan dome and the open flux above the fan dome, respectively. Panel (f): Time-distance diagram along the direction of the white line in panel (c). An animation of the whole evolution process of the fan-spine system is available from 22:00 UT to 22:58 UT. The duration of the animation is 9 s.
• Figure 3: (a)$-$(f): HRIEUV 174Å sequence images showing the production of two current sheets. (d1)$-$(f1): Schematic diagrams of the evolutionary sequence of filament 2, corresponding to the respective time instances shown in panels (d)$-$(f). (i1)$-$(i3): Time-distance diagrams along the direction of the cyan arrows in panel (f). The dashed black line outlines the post-flare loop after the eruption of filament 2 in panel (f). The dashed red line in panel (i3) represents the position from which the light curve was extracted for wavelet analysis, with the results presented in Figs. 7(a1)$-$7(a3).
• Figure 4: (a)$-$(f): Sequence of HRIEUV 174 Å images illustrating the continuous interchange reconnection process. (b) Three groups of loops (yellow arrows). (c): The dashed black arrow shows the slipping motion of these three loops. (d): Reconnection site between these three loops and the ambient open fields (pink arrows). Open magnetic field lines of the three loops after the reconnection in panel (f) (dashed yellow lines). Panels (g)$-$(i) show a curtain-like feature. (i1)$-$(i3): Time-distance diagrams along the direction of the dashed white lines in panel (i). The dotted blue lines in panels (i1)$-$(i3) trace the inclined ridges that correspond to the plasma outflows along the curtain feature. The speeds were calculated by performing a linear fit on the height-time measurements. The “as” is an abbreviation for “average speed”. The dashed red lines in panels (i1)$-$(i3) mark the locations from which the light curves were extracted for wavelet analysis, with the results presented in Figs. 7 (b) to 7(d).
• Figure 5: Panels (a)$-$(f): Final evolution process of the fan-spine-like system. The black arrows denote another filament (filament 3) in panels (d)$-$(e).