Fine Structures of Tiny Quiet Sun Jets Observed by Solar Orbiter and Big Bear Solar Observatory

TL;DR

This work addresses how tiny quiet-Sun EUV jets couple with chromospheric dynamics by leveraging the first joint high-resolution observations from Solar Orbiter's EUI/HRI and GST/VIS. The authors apply time-distance analyses, magnetic-field context from HMI/NIRIS, and an AI-assisted differential emission measure (DEM) to characterize plasma properties and energetics, revealing a helical coronal jet with a substantial thermal energy component and a nearby envelope of sheath-like chromospheric flows. They interpret the results in the framework of interchange reconnection via a thin flux tube model and a chromospheric jet scenario, finding an energy budget of about $E\approx 1.9\times 10^{26}$ erg (87% thermal, 13% kinetic) and a footpoint separation of about $1.6$ Mm with a magnetic flux around $5.4\times 10^{17}$ Mx, consistent with the smallest quiet-Sun magnetic features. The study highlights the intricate corona–chromosphere coupling and demonstrates how high-resolution, multi-instrument observations can constrain reconnection-driven processes and their role in small-scale solar ejections across atmospheric layers.

Abstract

We present the first joint high-resolution observations of small-scale EUV jets using Solar Orbiter(SolO)'s Extreme Ultraviolet Imager and High Resolution Imager (HRI) and H$α$ imaging from the Visible Imaging Spectrometer (VIS) installed on the 1.6~m Goode Solar Telescope (GST) at the Big Bear Solar Observatory (BBSO). These jets occurred on 2022-10-29 around 19:10 UT in a quiet Sun region and their main axis aligns with the overarching magnetic structure traced by a cluster of spicules. However, they develop a helical morphology, while the H$α$ spicules maintain straight, linear trajectories elsewhere. Alongside the spicules, thin, elongated red- and blue-shifted H$α$ features appear to envelope the EUV jets, which we tentatively call sheath flows. The EUI jet moving upward at speed of ~110 km/s is joined by strong H$α$ red-shift ~20 km/s to form the bidirectional outflows lasting ~2 min. Using AI-assisted differential emission measure (DEM) analysis of SolO's Full Sun Imager (FSI) we derived total energy of the EUV jet as ~$1.9 \times 10^{26}$ erg with 87% in thermal energy and 13% in kinetic energy. The parameters and morphology of this small-scale EUV jet are interpreted based on a thin flux tube model that predicts Alfvenic waves driven by impulsive interchange reconnection localized as narrowly as ~1.6 Mm with magnetic flux of ~$5.4\times 10^{17}$ Mx, belonging to the smallest magnetic features in the quiet Sun. This detection of intricate corona--chromospheric coupling highlights the power of high-resolution imaging in unraveling the mechanisms behind small-scale solar ejections across atmospheric layers.

Figures (6)

• Figure 1: Projection effects of the quiet-region EUV jet for multiple instruments. ($a$) SDO/AIA 171 Å with a small jet encloseed by the dotted box. ($b$) SolO's EUI/HRI$_{\rm EUV}$ 174 Å of the same region. The three-color half circles are meant to show the projection effect. Model loops are constructed in the disk center and projected back to the two locations. Other images in the small FOV around the jets shown in ($c$--$e$) include a tilt-adjusted EUI/HRI$_{\rm EUV}$ 174 Å ($c$), the SDO/AIA 171 Å ($d$) and H$\alpha$ wing $\pm$0.8 Å images ($e,f$). As a reference, we overlay the outline of the AIA 171 Å profile (blue contour from $d$) on other images ($c, e, f$). A composite image of the H$\alpha$ blue wing image (gray-scale) and EUI/HRI$_{\rm EUV}$ in yellow color shades ($g$) shows different morphologies. The observation time of AIA and GST is delayed by 4.5 min from that of EUI/HRI$_{\rm EUV}$.
• Figure 2: The evolution of EUI/HRI$_{\rm EUV}$ jet structure at 174 Å (top), difference between H$\alpha \pm$0.8 Å wing images (middle), and pseudo-Dopplergram from 5 wavelength point GST/VIS images (bottom). They show pre-existing strand ($a$), knot-like structure ($b$), multiple stripes ($b$--$d$) and a rapidly turning or bending structure ($e, j, o$) as well as sheath flows (arrows in $f$--$i$, $k$--$n$). The Dopplergrams show strong redshift components concentrated under the EUV jets.
• Figure 3: EUV TD maps and time profiles of EUV flux, H$\alpha$ Doppler motions and magnetic flux. (a) An EUI/HRI$_{\rm EUV}$ image with slit positions set for the TD maps. (b--d) TD maps for EUI along the slits #1--3 show upward speeds of 110--120 km s$^{-1}$, and the evolving helical structure (white arrow). Time profiles of (e) the EUV flux, (f) H$\alpha$ Dopplershift fluxes, and (g) magnetic fluxes. In (g), the red (blue) curve corresponds to the positive (negative) flux. In (c--g) the vertical guides lines indicate the start (dotted line) and the end (dashed) times of the two jets. Animation of the panel (a) from 19:00:00 UT to 19:21:40 UT is available.
• Figure 4: Correspondence between the magnetic fields, spicules, and the EUV jet. (a) The H$\alpha$ spicule trajectories readouts (green lines) from the GST/VIS $-$0.8 Å image are taken as proxy for the magnetic field lines, and copied to (b-d). (b) SDO/AIA 171 Å image with the LOS magnetogram (contours). (c) Same as (a) over the the Dopplergram with the blue/red colors representing blueshift and redshits. The field lines are colored magenta in this panel. (d) An SDO/HMI LOS magnetogram with the contours at the levels of $-$40 G (blue) and $+30$ G (red). These contours are over-plotted in panels (a--c) as well. (e) The three panels are GST/NIRIS LOS magnetic fields in the small FOV (cyan box in d) in units of arcsec. (f) NIRIS magnetogram in the same FOV at another time in units of Mm. Two guide lines are the slits for scanning the 1-D magnetic field distributions. (g) Distribution of the vertical magnetic field, $B_z$, read along the two slits. Animation shows the panels (a) and (c) from 19:06:16 UT to 19:20:55 UT.
• Figure 5: DEMs of the jet region derived from EUV images. (a) The six panels show one EUI/FSI 174 Å image and five AIA equivalent images generated by deep learning. The red box indicates the pixels used to calculate the DEM. (b) The DEM derived from the SDO/AIA images (green) with AI-generated EUV images with observed FSI 174 Å image (purple). The solid lines represent the DEM profiles when the jet activity is strong (19:10:20 UT), while the dashed lines correspond to the profiles when the jet diminished (19:20:50 UT). (c) The net DEM calculated from the difference EUV images between the jet maximum and the jet quiet time.