Abstract
The topic of this review paper is on the influence of solar wind turbulence on shock propagation and its consequence on the acceleration and transport of energetic particles at shocks. As the interplanetary shocks sweep through the turbulent solar wind, the shock surfaces fluctuate and ripple in a range of different scales. We discuss particle acceleration at rippled shocks in the presence of ambient solar-wind turbulence. This strongly affects particle acceleration and transport of energetic particles (both ions and electrons) at shock fronts. In particular, we point out that the effects of upstream turbulence is critical for understanding the variability of energetic particles at shocks. Moreover, the presence of pre-existing upstream turbulence significantly enhances the trapping near the shock of low-energy charged particles, including those near the thermal energy of the incident plasma, even when the shock propagates normal to the average magnetic field. Pre-existing turbulence, always present in space plasmas, provides a means for the efficient acceleration of low-energy particles and overcoming the well known injection problem at shocks.
Highlights
Understanding shocks and its particle acceleration in the solar wind is an important topic in heliophysics, for both the effects of space weather and basic physics of shocks and particle energization
At 1 astronomical unit (AU), these shocks are mostly driven by coronal mass ejections, with a smaller population driven by Stream Interaction Regions (SIRs) (Sheeley et al, 1985; Richardson and Cane, 2010; Borovsky, 2020)
Strong energetic particles observed in the vicinity of interplanetary shocks are often termed as “Energetic Storm Particles” (ESP) (Bryant et al, 1962; Gosling et al, 1981), to distinguish them from the solar energetic particles (SEPs) accelerated close to the Sun, the SEPs can be well accelerated by the coronal counterpart of the interplanetary shock driven by the same coronal mass ejection (Kallenrode, 1996; Reames, 1999)
Summary
Understanding shocks and its particle acceleration in the solar wind is an important topic in heliophysics, for both the effects of space weather and basic physics of shocks and particle energization. The turbulent magnetic field can interact with the shock waves, distorting their surfaces, leading to shock ripples (Neugebauer and Giacalone, 2005) and enhance the downstream magnetic fluctuations (Zank et al, 2003; Lu et al, 2009) It is important for efficient particle acceleration (Giacalone, 2005; Jokipii and Giacalone, 2007; Guo et al, 2010; Guo and Giacalone, 2010; Guo and Giacalone, 2015). Where f0 is a normalization constant, r is the ratio of the downstream to upstream density, U1 is the upstream flow speed in the shock frame, and H(p) is the Heaviside step function This solution is obtained by solving the Parker transport equation (see a discussion in Section 3) for a onedimensional time-steady shock at x 0.
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