Journal Article

PUBDB-2024-08055

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Observations of Turbulence and Particle Transport at Interplanetary Shocks: Transition of Transport Regimes

Zhao, S. (Corresponding author)DESY* ; Yan, H.DESY* ; Liu, T. Z.

2025
Institute of Physics Publ. London

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Please use a persistent id in citations: doi:10.3847/1538-4357/adc378  doi:10.3204/PUBDB-2024-08055

Abstract: The transport of energetic particles is intimately related to the properties of plasma turbulence, a ubiquitous dynamic process that transfers energy across a broad range of spatial and temporal scales. However, the mechanisms governing the interactions between plasma turbulence and energetic particles are not completely understood. Here we present comprehensive observations from the upstream region of a quasi-perpendicular interplanetary (IP) shock on 2004 January 22, using data from four Cluster spacecraft to investigate the interplay between turbulence dynamics and energetic particle transport. Our observations reveal a transition in energetic proton fluxes from exponential to power-law decay with increasing distance from the IP shock. This result provides possible observational evidence of a shift in transport behavior from normal diffusion ($\langle (\Delta \mathbf{x})^2\rangle \propto t$) to superdiffusion ($\langle (\Delta \mathbf{x})^2\rangle \propto t^\alpha$, with $\alpha>1$), where $\Delta \mathbf{x}$ is particle displacement over the timescale $t$. This transition correlates with an increase in the time ratio from $\tau_s/\tau_{c}<1$ to $\tau_s/\tau_{c}\gg1$, where $\tau_s$ is the proton isotropization time, and $\tau_{c}$ is the turbulence correlation time. Additionally, the frequency-wavenumber distributions of magnetic energy in the power-law decay zone indicate that energetic particles excite linear Alfv\'en-like harmonic waves through gyroresonance, thereby modulating the original turbulence structure. These findings provide valuable insights for future studies on the propagation and acceleration of energetic particles in turbulent astrophysical and space plasma systems.

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Contributing Institute(s):

1. Plasma-Astrophysik (Z_PLAS)

Research Program(s):

1. 613 - Matter and Radiation from the Universe (POF4-613) (POF4-613)

Experiment(s):

1. No specific instrument

Appears in the scientific report 2025

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