3D structures of the base of small-scale recurrent jets revealed by Solar orbiter

TL;DR

The study addresses how small-scale solar jets are structured at their bases and how their magnetic topology governs their dynamics. By combining Solar Orbiter’s high-resolution EUV imaging with SDO data and applying both potential-field and magneto-hydrostatic extrapolations, the authors reconstruct the 3D magnetic geometry and reveal a progression from a simple single-null fan–spine configuration to a complex multi-null curtain over four eruptions. They show that jet bases are multi-thermal and that flows are confined within quasi-separatrix layers, with the strongest speeds and hottest plasma near null points, consistent with successive reconnection episodes driven by flux cancellation. The findings provide direct observational evidence that dynamic changes in null-point geometry modulate jet morphology and energetics, highlighting the value of stereoscopic, high-resolution observations and magnetic modeling for understanding energy release in the solar atmosphere.

Abstract

Solar jets, characterized by small-scale plasma ejections along open magnetic field lines or the legs of large-scale coronal loops, play a crucial role in the dynamics of the solar atmosphere. Although spectral and EUV images have been widely used to analyze the formation and evolution of jets, the detailed 3D structure at the base of the jet has not been studied in detail due to the limitations in the spatial resolution of observations. Solar Orbiter enables us to investigate the structure of solar jets with much higher spatial and temporal resolutions and from a different angle than from Earth. By combining observations made by instruments onboard Solar Orbiter with data from the SDO, we analyzed recurrent solar jets originating in a mixed-polarity region near an active region. Additionally, we employed potential field and magnetohydrostatic extrapolation techniques to determine the magnetic field topology associated with the jets. The jets display dynamic, multi-strand outflows emanating from compact bright kernels above the magnetic inversion line, with apparent speeds exceeding 100 km/s. Magnetic field evolution reveals continuous flux cancellation at the jet footpoints. Throughout the sequence, base flows are confined within quasi-separatrix layers, with the highest velocities and temperatures located near coronal null points. Over four eruptions, the magnetic topology evolves from a simple fan-spine configuration with a single null to a more complex dome-shaped base containing multiple nulls with separatrix curtain, accompanied by a morphological transition from narrow, well-collimated spire to broader, fragmented outflows. These results provide the first direct observational evidence that dynamic changes in null-point geometry modulate jet morphology and energetics via successive reconnection episodes.

Figures (9)

• Figure 1: Overview of the recurrent jet events on 7 April 2023. (a) Relative positions of the Sun, SDO, and Solar Orbiter. (b) Full-disk image of the Sun taken by SDO/AIA at 171 Å. (c) SDO/AIA 171 Å image of a sub-region in AR 13270. (d) Composite map combining the full-disk image of SO/EUI-FSI at 174 Å, the SO/EUI-HRI 174 Å image, and the SO/SPICE "O V 760.2 ... Ne VIII 770 (Merged)" spectral window. (e) SO/EUI-HRI 174 Å image focusing on AR 13270. (f) Zoom into the recurrent jets observed in AR 13270 as seen by SO/EUI-HRI. The blue and red arrows in panels (c) and (f) indicate two distinct jet structures.
• Figure 2: SDO/AIA 94 Å (panels (a1$-$a5)), 171 Å (panels (b1$-$b5)), 304 Å (panels (c1$-$c5)) and SO/EUI-HRI 174 Å (panels (d1$-$d5)) images showing the recurrent jets during their four eruptions. The dotted lines in the second column indicate the positions where the slices are taken, and the temporal evolution of these slices is shown in Figure \ref{['Fig3']}. The red arrows in panels (a4), (a5), (d3) and (d5) indicate the bright kernels at the jet base.
• Figure 3: Time-slice plots of the SDO/AIA 94 Å (panel (a)), 171 Å (panel (b)), and 304 Å (panel (c)) images along the spire of the southern jet marked by the dotted lines in Fig. \ref{['Fig2']}. The solid lines indicate the trajectories of the jet structures, with the corresponding velocities displayed alongside.
• Figure 4: Panels (a1)$-$(a6): SO/EUI-HRI 174 Å images showing the evolution of the third eruption of the recurrent jets. In panels (a3) and (a5), the red arrows denote two bright points. Panel (b): Temporal evolution along the position indicated by the line 'A--B' in panel (a3). Panel (c): Time-distance plot along the position marked by the line 'C--D' in panel (a3).
• Figure 5: Evolution of the magnetic structures at the footpoints of the recurrent jets. Panel (a): SO/PHI-HRT $B_{\mathrm{LOS}}$ map overlaid with SO/EUI-HRI 174 Å images of the entire active region (AR). The red square outlines the sub‐field shown in the subsequent panels where the recurrent jets occur. Panel (b): SO/EUI-HRI 174 Å image cropped to the red‐boxed region in (a). Panel (c1): Co‐spatial SO/PHI-HRT magnetogram of the same sub‐field. Panels (c2)–(c4): Temporal sequence of magnetograms showing the evolution of the magnetic field in the jet footpoint regions. The green and red circles enclose the north and south jets, respectively. These regions were chosen to remain as isolated as possible from surrounding flux concentrations. Panels (d) and (e): Time series of the magnetic flux calculated within the green and red circles, respectively, illustrating the flux changes in the two jet footpoint regions.