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On the Origin of Coronal Picoflare Jets

Annu Bura, Daniel Nóbrega-Siverio, Tanmoy Samanta, Jayant Joshi

Abstract

Small-scale jet-like eruptions, such as picoflare jets and jetlets, are recognized as potential contributors to coronal heating and solar wind acceleration, yet their physical origin is still not fully established. Using ultra-high-resolution extreme ultraviolet imaging datasets from the Extreme Ultraviolet Imager on board the Solar Orbiter mission, we investigate tiny coronal jets observed off-limb in the Sun's polar regions. Visual inspection reveals that the majority of these jets exhibit distinct morphological features, including a bright spire accompanied by a dark eruptive jet component. We analyzed eleven of these jets in detail and found that their spatial and temporal scales are comparable to previously reported jetlets, while their kinetic energies are two to three orders of magnitude lower, placing them in the picoflare regime. The bright and dark components show distinct dynamics, with the dark structures generally displaying lower speeds. A comparison with coordinated Interface Region Imaging Spectrograph and the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory data, together with 2.5D radiative-MHD simulations performed with the Bifrost code, reveals a one-to-one morphological correspondence between the dark counterparts and cool chromospheric surges accompanying the bright jet spire. This association suggests that flux emergence and magnetic reconnection at low atmospheric heights may produce coupled bright-dark structures, providing a plausible mechanism for the generation of picoflare jets. Our results demonstrate Solar Orbiter's ability to resolve the dynamics of small-scale jets and place new constraints on their origin.

On the Origin of Coronal Picoflare Jets

Abstract

Small-scale jet-like eruptions, such as picoflare jets and jetlets, are recognized as potential contributors to coronal heating and solar wind acceleration, yet their physical origin is still not fully established. Using ultra-high-resolution extreme ultraviolet imaging datasets from the Extreme Ultraviolet Imager on board the Solar Orbiter mission, we investigate tiny coronal jets observed off-limb in the Sun's polar regions. Visual inspection reveals that the majority of these jets exhibit distinct morphological features, including a bright spire accompanied by a dark eruptive jet component. We analyzed eleven of these jets in detail and found that their spatial and temporal scales are comparable to previously reported jetlets, while their kinetic energies are two to three orders of magnitude lower, placing them in the picoflare regime. The bright and dark components show distinct dynamics, with the dark structures generally displaying lower speeds. A comparison with coordinated Interface Region Imaging Spectrograph and the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory data, together with 2.5D radiative-MHD simulations performed with the Bifrost code, reveals a one-to-one morphological correspondence between the dark counterparts and cool chromospheric surges accompanying the bright jet spire. This association suggests that flux emergence and magnetic reconnection at low atmospheric heights may produce coupled bright-dark structures, providing a plausible mechanism for the generation of picoflare jets. Our results demonstrate Solar Orbiter's ability to resolve the dynamics of small-scale jets and place new constraints on their origin.
Paper Structure (9 sections, 5 figures)

This paper contains 9 sections, 5 figures.

Table of Contents

  1. Introduction
  2. Data Analysis, Results and Discussion
  3. Observations and Data Reduction
  4. Numerical Experiment
  5. Dynamical Properties of Bright and Dark Structures
  6. Kinetic Energy of Jets
  7. Comparison with Flux Emergence Simulation
  8. Chromospheric Nature of Dark Structure
  9. Summary

Figures (5)

  • Figure 1: Examples of jets observed off-limb in the Sun's polar regions using HRI$_{\mathrm{EUV}}$ on board Solar Orbiter with a passband centered at 174 Å, each accompanied by a narrow, collimated dark structure indicated by white arrows. These jets are selected from three datasets: the north pole observation on September 14, 2021 (Jet 1), the south pole observations on September 14, 2021 (Jets 2-3), and on March 30, 2022 (Jets 4-9). An animation of this figure is available online. The real-time duration of the animation is 10 s.
  • Figure 2: Width estimation for jets observed in HRI$_{\mathrm{EUV}}$. Panel (A) shows the observation of Jet 1 in HRI$_{\mathrm{EUV}}$ with a white artificial slit marking the location used to extract the intensity profile. Panel (B) shows the corresponding intensity profile (histogram mode), where two Gaussian functions are fitted to the peak (red curve) and dip (blue curve) in the profile, corresponding to the adjacent bright and dark structures, to estimate their FWHM. Panels (C) and (D) show a similar analysis for jet 6. The green dashed curve in panels (A) and (C) represents the spline-interpolated curve from the jet base at the visible surface to the top of the spire, used to estimate the jet lengths.
  • Figure 3: Speed estimation of jets observed in HRI$_{\mathrm{EUV}}$. Panel (A) shows Jet 4 in HRI$_{\mathrm{EUV}}$ with two artificial slits overlaid: a white rectangle (5 pixels wide) and a yellow rectangle (7 pixels wide), used to construct space-time diagrams for the bright jet spire and the associated dark structure, respectively. Panels (B) and (C) display the resulting space-time plots along these artificial slits. For the bright jet spire, the maximum intensity values along the white slit are used to construct the space–time diagram, and the propagation speed is obtained by tracking the inclined intensity ridge corresponding to the upper part of the spire. For the dark structure, the minimum intensity values along the yellow slit are used in an analogous manner. Panels (D)–(F) present the same analysis for Jet 5.
  • Figure 4: Temporal evolution of jets and comparison with simulation. Panel (A): shows the temporal evolution of Jet 10 observed on April 5, 2024. Panel (B): shows the temporal evolution of Jet 1 observed on September 14, 2021, during the north polar observation. Panel (C): shows the temporal evolution of Jet 7 observed on March 30, 2022. Panel (D): Comparison with a flux emergence simulation from 2018ApJ...858....8N, showing synthetic emission in the HRI$_{\mathrm{EUV}}$ 174 Å filter. Blue and red contours correspond to plasma at T = 0.1 MK and T = 2 MK, highlighting the locations of the cool and hot ejections, respectively. The red, green, cyan, and white arrows mark the JBP, current sheet, bright spire, and dark structure, respectively. Panels (E–F) show the temporal evolution of the temperature and density maps of the jets, with the same temperature contours from Panel D overlaid. Note that the 2.5D synthetic 174 Å image appears dark in regions where plasma temperatures lie outside the passband’s sensitivity, such as the $\sim$2 MK spire and $\sim$0.1 MK dark jet; however, the temperature maps clearly reveal them. The animation of panels (D)-(F) is available online. The real-time duration of the animation is 13 s.
  • Figure 5: Panel (A): Temporal evolution of Jet 11 observed in the AIA 171 Å passband on August 7, 2019. The jet base exhibits a distinct inverted “Y” (or “$\lambda$”) morphology, most clearly visible at the 22:13:57 timestamp. Panel (B): coordinated IRIS observation showing the temporal evolution of raster maps, constructed by extracting intensity at 2796.2 Å in the Mg2 k spectral window. The green contour outlines the dark surge observed in Mg2 k 2796.2 Å and is overplotted in the AIA 171 Å images in panel (A), revealing that the dark surge appears adjacent to the bright jet spire. The white vertical dashed line in the AIA panels marks the FOV of the IRIS raster maps. An animation of this figure is available online. The real-time duration of the animation is 5 s.