Thin coronal jets and plasmoid-mediated reconnection: Insights from Solar Orbiter observations and Bifrost simulations

TL;DR

The study leverages Solar Orbiter's HRIEUV observations to resolve ultra-narrow coronal jets originating from CBPs, uncovering widths of 253–706 km and lengths up to 22 Mm, with 30–85% brightness enhancements. By combining eleven CBP datasets with 2D radiative-MHD Bifrost simulations, the authors identify both direct plasmoid formation within current sheets (e.g., a 332 km plasmoid in Case 08) and indirect, boomerang-like signatures in the outflow, mirroring synthetic EUV emission. The simulations validate that plasmoid-mediated reconnection in a fan-spine topology can produce jetting and current-sheet structures comparable to the observations, even when degraded to HRIEUV-like resolution. These results demonstrate Solar Orbiter's capability to probe sub-megamerter reconnection scales and suggest that CBP-driven, plasmoid-rich reconnection may play a significant role in coronal dynamics and possibly in solar wind structuring, motivating extensive future statistics and multi-wavelength campaigns.

Abstract

Coronal jets are ubiquitous, collimated million-degree ejections that contribute to the energy and mass supply of the upper solar atmosphere and the solar wind. Solar Orbiter provides an unprecedented opportunity to observe fine-scale jets from a unique vantage point close to the Sun. We aim to uncover thin jets originating from Coronal Bright Points (CBPs) and investigate observable features of plasmoid-mediated reconnection. We analyze eleven datasets from the High Resolution Imager 174 Å of the Extreme Ultraviolet Imager (HRIEUV) onboard Solar Orbiter, focusing on narrow jets from CBPs and signatures of magnetic reconnection within current sheets and outflow regions. To support the observations, we compare with CBP simulations performed with the Bifrost code. We have identified thin coronal jets originating from CBPs with widths ranging from 253 km to 706 km: scales that could not be resolved with previous EUV imaging instruments. Remarkably, these jets are 30-85% brighter than their surroundings and can extend up to 22 Mm while maintaining their narrow form. In one of the datasets, we directly identify plasmoid-mediated reconnection through the development within the current sheet of a small-scale plasmoid that reaches a size of 332 km and propagates at 40 km/s. In another dataset, we infer plasmoid signatures through the intermittent boomerang-like pattern that appears in the outflow region. Both direct and indirect plasmoid-mediated reconnection signatures are supported by comparisons with the synthetic HRIEUV emission from the simulations.

Figures (10)

• Figure 1: Context for the Solar Orbiter HRI$_{\mathrm{EUV}}$ observations of the eleven cases showing thin coronal jets (gray arrows) associated with CBPs that are analyzed in this paper. The intensity of the images is given in DN and times are in UT. The details of each observation are provided in Table \ref{['tab:solo_observations']}. Individual movies for each of the cases are available https://zenodo.org/records/16903189.
• Figure 2: Analysis of Case 01 during the gentle reconnection phase at 05:19:30 UT (top row) and the enhanced phase at 05:44:00 UT (bottom row). Panels (a) and (d) show the CBP and the associated thin coronal jets (gray arrows). Panels (b) and (e) display space–time maps obtained by taking the maximum intensity along the width $W$ of the bent red slit of length $L$ shown in panels (a) and (d), respectively. Panels (c) and (f) illustrate the widths of the narrow jets, calculated using the FWHM at $L = 7.5$ Mm, as indicated by the blue dotted lines in panels (a) and (d), respectively.
• Figure 3: Plasmoid signatures in Case 08. Panel (a): Context view showing the CBP and the current sheet within a rectangle of length $L$ and width $W$. Panel (b): Zoomed-in view of the blue rectangle shown in panel (a), highlighting the illustrative plasmoid with a cyan arrow. Panel (c): Space–time plot of the current sheet, obtained by taking the maximum intensity along the $W$ direction. The cyan dashed line indicates the trajectory of the plasmoid. Panel (d): Intensity profiles along the current sheet at different times, illustrating the evolution of the plasmoid indicated in panel (c). An animation of this figure is available https://zenodo.org/records/16903189 showing the evolution of the plasmoid between 19:10:35 UT and 19:11:10 UT.
• Figure 4: Same as Figure \ref{['fig:figure_03']}, but for the plasmoid signatures in the 2D CBP simulation by Nobrega-Siverio_Moreno-Insertis:2022. The top row shows the HRI$_{\mathrm{EUV}}$ synthetic emissivity at the original resolution of the numerical experiment ($\approx 16$ km). The bottom row shows the results after degrading the resolution to match the best case achievable by HRI$_{\mathrm{EUV}}$ in our study (pixel size of 108 km). An animation of this figure is available https://zenodo.org/records/16903189 showcasing the plasmoid evolution between $t=29.9$ and $t=30.0$ min.
• Figure 5: Indirect signatures of plasmoid-mediated reconnection in Case 01. Panel (a): Context view illustrating the CBP and the associated ejections. The arrows mark the signatures that are interpreted as consequences of plasmoid-mediated magnetic reconnection. Panel (b): Space–time map obtained by sampling the intensity along the slit of length $L$ shown in panel (a). Panel (c): Intensity profiles along the slit at 05:44:00 UT. An animation of this figure is available https://zenodo.org/records/16903189, showing the time evolution between 05:43:48 UT and 05:44:12 UT.