Abstract
Energetic particles are ubiquitous in the interplanetary space and their transport properties are strongly influenced by the interaction with magnetic field fluctuations. Numerical experiments have shown that transport in both the parallel and perpendicular directions with respect to the background magnetic field is deeply affected by magnetic turbulence spectral properties. Recently, making use of a numerical model with three dimensional isotropic turbulence, the influence of turbulence intermittency and magnetic fluctuations on the energetic particle transport was investigated in the solar wind context. Stimulated by this previous theoretical work, here we analyze the parallel transport of supra-thermal particles upstream of interplanetary shock waves by using in situ particle flux measurements; the aim was to relate particle transport properties to the degree of intermittency of the magnetic field fluctuations and to their relative amplitude at the energetic particle resonant scale measured in the same regions. We selected five quasi-perpendicular and five quasi-parallel shock crossings by the ACE satellite. The analysis clearly shows a tendency to find parallel superdiffusive transport at quasi-perpendicular shocks, with a significantly higher level of the energetic particle fluxes than those observed in the quasi-parallel shocks. Furthermore, the occurrence of anomalous parallel transport is only weakly related to the presence of magnetic field intermittency.
Highlights
Understanding the transport properties of energetic particles in space and astrophysical plasmas is crucial for assessing particle acceleration and propagation
For energetic particles accelerated at collisionless shocks, superdiffusive transport has been deduced from the analysis of energetic particle time profiles upstream of heliospheric shocks [5,6,7,8,9,10,11], from the upstream precursor of supernova remnant shocks detected in the X-rays [12,13], from the galactic cosmic ray spectra [14], from the discrepancy between the radio-derived and X-ray-derived Mach numbers at the galaxy cluster merger shocks [15,16], and from self-consistent particle-in-cell simulations of protons accelerated at shocks [17]
Using in situ spacecraft data, we investigated the influence of the turbulence properties on the energetic particle transport upstream of interplanetary shocks, in order to understand whether the occurrence of the power-law time profiles for energetic particles corresponds to particular turbulence conditions
Summary
Understanding the transport properties of energetic particles in space and astrophysical plasmas is crucial for assessing particle acceleration and propagation. Implementing a 3D isotropic model of static magnetic field turbulence [31] with adjustable turbulent spectral extension, fluctuation amplitude, and the degree of scale-dependent non Gaussianity, called magnetic intermittency [32], the transport of energetic particles in the direction parallel and perpendicular to the mean field has been investigated [33,34]. Intermittency only weakly affects the duration of the transient phase in the parallel direction, being the onset of the diffusive propagation a bit delayed in the presence of intermittency with respect to the presence of a Gaussian fluctuation field This is in full agreement with the cosmic-ray diffusion studied in a test-particle simulation in 3D turbulence by [33] (see their Figure 5). We analyzed in synergy the high-resolution magnetic field, plasma, and energetic particle measurements
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
