Dynamics of Null-points across Shocks Interacting with Preexisting Turbulence
Year: 2026
Type: article
Abstract: In this study, we utilize 2.5D resistive magnetohydrodynamic (MHD) simulations to examine the generation and evolution of plasmoids resulting from the interaction between shock waves and turbulence in interplanetary space. We focus on (quasi-)perpendicular shock geometries with an out-of-plane mean magnetic field to investigate the impact of preexisting large-scale turbulent magnetic fluctuations upstream on MHD shock waves and on magnetic reconnection in the downstream region. Our findings reveal several key insights. First, the magnetic turbulence spectra exhibit three ranges: a low- k range characterized by cascading, a mid- k range potentially mediated by reconnection, and a high- k range corresponding to resistive diffusion. Importantly, these spectral features, including their characteristic breaks and slopes, remain invariant across the shock transition. Second, in all cases, the downstream occurrence of X-points and O-points increases, saturates to a peak value for a certain interval, and gradually decreases away from the shock. This behavior of X-points is consistent with the in situ measurements taken by the Magnetospheric Multiscale mission at Earth’s bow shocks. Third, the resistive simulations allow for the explicit calculation of the magnetic reconnection rate per unit area in the x–y plane, indicating a higher rate per unit area downstream than upstream. This is consistent with the increased occurrence of X-points.
Source: The Astrophysical Journal
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $4,499
Awards: THE PARTICLE ACCELERATION AT INTERPLANETARY SHOCKS HAS BEEN AN ACTIVE FIELD OF OBSERVATIONAL AND THEORETICAL INVESTIGATION IN THE PAST FIVE DECADES; HOWEVER THE SPATIAL DISTRIBUTION OF ENERGETIC PARTICLES ACROSS THE SHOCK CAN NOT BE REPRODUCED BY CURRENT THEORETICAL MODELS IN SEVERAL CASES. WE PROPOSE TO INVESTIGATE THE LOCAL INTENSITY ENHANCEMENTS AT THE SHOCK (SO-CALLED "SPIKES") OF SUPRA-THERMAL PARTICLES HAVING A SPEED WITHIN ONE ORDER OF MAGNITUDE GREATER THAN THE SHOCK SPEED IN THE UPSTREAM FLUID REST FRAME. THIS REGIME HOLDS BEYOND THE VALIDITY OF THE STANDARD DIFFUSIVE SHOCK ACCELERATION MODEL AND HAS BEEN POORLY STUDIED SO FAR. WE CONSIDER THIS WORK AN OVERDUE AND INNOVATIVE APPROACH TO THE SO-CALLED "INJECTION PROBLEM". WE PROPOSE A DATA-GUIDED STUDY TO COMBINE: 1) ANALYSIS AND INTERPRETATION OF INTERPLANETARY SHOCKS HIGH TIME RESOLUTION DATA COLLECTED BY ENERGETIC PARTICLE DETECTORS AND MAGNETOMETERS AT 1 AU ONBOARD ACE (ADVANCED COMPOSITION EXPLORER) AND STEREO (SOLAR TERRESTRIAL RELATIONS OBSERVATORY) A/B; 2) THEORY AND ADVANCED NUMERICAL SIMULATIONS AT SHOCKS PROPAGATING IN A TURBULENT MEDIUM TO INTERPRET THE AVAILABLE DATA. AN ANALYSIS RECENTLY CONDUCTED HAS SUGGESTED THAT THE OBSERVED ANISOTROPY AT SHOCK SPIKES RESULTS FROM BIDIRECTIONAL STREAMING OF IONS ALONG FIELD LINES THAT CROSS THE SHOCK MULTIPLE TIMES AT ODDS WITH A PREVIOUS INTERPRETATION BASED ON PILE-UP OF REFLECTED IONS; WE WILL COMPARE SUCH INTERPRETATIONS IN DETAIL. WE HAVE IDENTIFIED TWO CASES OF SHOCK SPIKE THAT WE WILL ANALYZE IN DETAIL AND WE WILL LOOK FOR OTHER CASES FROM EXISTING AND UPCOMING SPACECRAFT ARCHIVES. WE WILL COMPARE THOSE DATA WITH OUR MULTIPLE-APPROACH SIMULATIONS TO INVESTIGATE THE ORIGIN OF THE SHOCK SPIKES THEIR ANISOTROPY AND TIME-EVOLUTION., G8457443216
OpenAlex ID: W7124423874