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Rotation of a Solar Jet Driven by Plasma Flow along Helical Magnetic Fields in an Active Region

Lei Huang, Yang Guo, Zhen Li, Jinhan Guo, Mingde Ding

Abstract

Solar jets, collimated plasma ejections driven by magnetic reconnection, play a vital role in energy transport and coronal heating. While rotational motions in jets are often attributed to magnetic field untwisting, alternative explanatory mechanisms remain possible. This study investigates a rotating jet in an active region observed on 2023 August 1 using multi-wavelength observations from Atmospheric Imaging Assembly (AIA), Chinese Ha Solar Explorer (CHASE), and Interface Region Imaging Spectrograph (IRIS), combined with a self-consistent time-dependent magnetofrictional (TMF) model and magnetohydrodynamic (MHD) simulation. Spectral diagnostics reveal coexisting red and blue shifts along the edges and central axis of the jet, indicating helical plasma motion within a twisted magnetic structure. Numerical simulations demonstrate that the jet's rotation arises from plasma propagating along helical open field lines, formed via reconnection between a pre-existing flux rope and overlying magnetic fields. Contrary to classical untwisting models, both linear and rotational velocities decrease with altitude during the jet propagation. These results highlight that the observed rotation results from plasma spiral motion along twisted fields rather than untwisting dynamics of the magnetic field itself, providing new insights into solar jet energetics and their connection to broader solar phenomena.

Rotation of a Solar Jet Driven by Plasma Flow along Helical Magnetic Fields in an Active Region

Abstract

Solar jets, collimated plasma ejections driven by magnetic reconnection, play a vital role in energy transport and coronal heating. While rotational motions in jets are often attributed to magnetic field untwisting, alternative explanatory mechanisms remain possible. This study investigates a rotating jet in an active region observed on 2023 August 1 using multi-wavelength observations from Atmospheric Imaging Assembly (AIA), Chinese Ha Solar Explorer (CHASE), and Interface Region Imaging Spectrograph (IRIS), combined with a self-consistent time-dependent magnetofrictional (TMF) model and magnetohydrodynamic (MHD) simulation. Spectral diagnostics reveal coexisting red and blue shifts along the edges and central axis of the jet, indicating helical plasma motion within a twisted magnetic structure. Numerical simulations demonstrate that the jet's rotation arises from plasma propagating along helical open field lines, formed via reconnection between a pre-existing flux rope and overlying magnetic fields. Contrary to classical untwisting models, both linear and rotational velocities decrease with altitude during the jet propagation. These results highlight that the observed rotation results from plasma spiral motion along twisted fields rather than untwisting dynamics of the magnetic field itself, providing new insights into solar jet energetics and their connection to broader solar phenomena.
Paper Structure (8 sections, 4 equations, 10 figures, 3 tables)

This paper contains 8 sections, 4 equations, 10 figures, 3 tables.

Table of Contents

  1. Introduction
  2. Observations
  3. Modeling Description
  4. Results
  5. Spectral Analysis
  6. Simulation Results
  7. Mechanical Energy Budget
  8. Summary and Discussion

Figures (10)

  • Figure 1: Jet formation process. (a)--(b) SDO/AIA observations in 171 $\mathrm{\AA}$ and 304 $\mathrm{\AA}$ at 02:30 UT before the jet formation; (c)--(d) Corresponding 171 $\mathrm{\AA}$ and 304 $\mathrm{\AA}$ observations during the jet eruption at 02:48 UT. The attached animation, displaying AIA 171 $\mathrm{\AA}$ and 304 $\mathrm{\AA}$ images from 02:30 UT to 03:15 UT, clearly reveals the entire sequence of events: the presence and subsequent uplift of a small filament at the base prior to the eruption, followed by its eruption, the triggering of the jet, and the rotational motion of the jet.
  • Figure 2: Jet dynamics in multi-wavelength observations. (a)--(c) Running difference AIA 304 $\mathrm{\AA}$ images showing pre-jet configuration: FP1 and FP2 denote twin footpoints of a twist magnetic flux rope, and FP3 marks one footpoint of the external open field lines, with yellow stars indicating magnetic reconnection sites. (d) coordinated observations of AIA 304 $\mathrm{\AA}$ and IRIS/SJI 1400 $\mathrm{\AA}$. (e)--(h) Jet eruption phase of AIA 304 $\mathrm{\AA}$ images with black rectangles highlighting bright plasma blocks. (i)--(l) Running difference AIA 304 $\mathrm{\AA}$ images during jet descending phase, with red tracers follow plasma motion trajectories.
  • Figure 3: CHASE H$\alpha$ spectroscopic diagnostics of the jet dynamics. (a)--(d) CHASE H$\alpha$ blue-wing (6562.82-1.1 Å), core (6562.82 Å), red-wing (6562.82+1.1 Å), and composite blue-red wing images at 02:47:26 UT. The black box shows the background profile reference region. (e)--(h) Corresponding spectral components at 02:49:48 UT. The black arrow marks the position of the jet, the green arrow marks a blue shift region to the right of the jet. (i) Doppler velocity map at 02:47:26 UT. (j)--(m) The original spectral line profiles of the four points from left to right in panel (d) and the net spectral line profiles after subtracting the background line profile. The green dashed line marks the wavelength corresponding the minimum intensity of the net spectral line profile.
  • Figure 4: IRIS Si IV spectroscopic diagnostics of the jet dynamics. (a) Image of IRIS/SJI 1400 $\mathrm{\AA}$ at 02:49 UT. The attached animation, displaying IRIS SJI 1400 $\mathrm{\AA}$ observations from 02:30 UT to 03:15 UT, clearly reveals the filament prior to its eruption and the subsequent rotational motion of the jet following the eruption. (b)--(c) Doppler velocity maps within the jet in the white box in panel (a) calculated by single Gaussian fitting and double Gaussian fitting, respectively. (d)--(f) Spectral line profiles of the three points from left to right in panel (b). The observed profiles (black) with single-Gaussian (green) and double-Gaussian (red) fits, where yellow/purple dashed curves represent two components of the double Gaussian fit.
  • Figure 5: Magnetic Topology in the TMF model. (a)--(b) Magnetic flux rope morphology in TMF model superimposed on pre-eruption SDO/AIA 304 $\mathrm{\AA}$ background at 02:24 UT. (c)--(d) Open field lines in TMF model overlaid on HMI magnetogram at 02:24 UT. The arrows mark the magnetic flux rope and the open field lines.
  • ...and 5 more figures