Bi-directional streaming of particles accelerated at the STEREO-A shock on 9th March 2008

Abstract

We present an interpretation of anisotropy and intensity of supra-thermal ions near a fast quasi-perpendicular reverse shock measured by Solar Terrestrial Relations Observatory Ahead (ST-A) on 2008 March 9th. The measured intensity profiles of the supra-thermal particles exhibit an enhancement, or "spike", at the time of the shock arrival and pitch-angle anisotropies before the shock arrival are bi-modal, jointly suggesting trapping of near-scatter-free ions along magnetic field lines that intersect the shock at two locations. We run test-particle simulations with pre-existing upstream magnetostatic fluctuations advected across the shock. The measured bi-modal upstream anisotropy, the nearly field-aligned anisotropies up to ~15 minutes upstream of the shock, as well as the "pancake-like" anisotropies up to ~10 minutes downstream of the shock are well reproduced by the simulations. These results, in agreement with earlier works, suggest a dominant role of the large-scale structure (100s of supra-thermal proton gyroradii) of the magnetic field in forging the early-on particle acceleration at shocks.

7 pages, 4 figures, MNRAS in press

References in corpus (4)

• Fractional Transport in Strongly Turbulent Plasmas
• First observations of irregular surface of interplanetary shocks at ion scales by Cluster
• Energetic particle transport across the mean magnetic field: before diffusion
• Localized enhancements of energetic particles at oblique collisionless shocks

Cited by in corpus (2)

• In-situ Measurement of the Energy Fraction in Supra-thermal and Energetic Particles at ACE, Wind, and PSP Interplanetary Shocks
• Density jump as a function of magnetic field strength for parallel collisionless shocks with anisotropic upstream pressure