Small-scale impulsive extreme-UV emission enhancements along network loops

¹ Max Planck Institute for Solar System Research, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
² Institute for Solar Physics (KIS), Georges-Köhler-Allee 401A, 79110 Freiburg, Germany

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 11 November 2025
Accepted: 28 March 2026

Abstract

Context. Network loops are a common feature in the quiet Sun. The physical processes sustaining their energy budget are still discussed.

Aims. We relied on a multi-instrumental (Solar Orbiter/EUI, Solar Orbiter/PHI, and IRIS) observation of a six-hour quiet-Sun region to measure the dynamics and the possible magnetic drivers of impulsive Extreme Ultraviolet (EUV) emission enhancements along network loops.

Methods. We report the detection of small-scale impulsive EUV emission enhancements with EUI/HRIEUV in three network loops. We selected four EUV emission enhancements to measure their plane-of-sky velocities in HRIEUV, their Doppler velocities in the Si IV line (log T = 4.8) with IRIS, and their possible relation to small-scale flux emergence and fluctuation in one of the loop footpoints.

Results. The plane-of-sky velocities of the four EUV emission enhancements have a component that seems to appear almost instantaneously along the loop (≥220 km s⁻¹), and two of them had a co-temporal component with a plane-of-sky velocity of up to (77 ± 19) km s⁻¹, starting near one of the loop footpoints. In one case, we measured a co-temporal intensity increase in the Si IV line with IRIS that is associated with Doppler velocities down to −32 km s⁻¹ and up to 18 km s⁻¹ along the line of sight. Finally, we measured cases of small-scale (≈8 × 10¹⁶ Mx) mixed-polarity field emergence and fluctuation near one of the loop footpoints.

Conclusions. We conclude that the fast components on the plane-of-sky are consistent with a thermal transfer or supersonic plasma flows, while the slower component is consistent with plasma flows. A possible physical origin for these EUV emission enhancements would be magnetic reconnection driven by either a photospheric motion of the loop footpoints or by the reconnection of the loop with small-scale magnetic bipoles.