On the Transmission of Turbulent Structures across the Earth’s Bow Shock

Abstract

Collisionless shocks and plasma turbulence are crucial ingredients for a broad range of astrophysical systems. The shock–turbulence interaction, and in particular the transmission of fully developed turbulence across the quasi-perpendicular Earth’s bow shock, is here addressed using a combination of spacecraft observations and local numerical simulations. An alignment between the Wind (upstream) and Magnetospheric Multiscale (downstream) spacecraft is used to study the transmission of turbulent structures across the shock, revealing an increase of their magnetic helicity content in its downstream. Local kinetic simulations, in which the dynamics of turbulent structures are followed through their transmission across a perpendicular shock, confirm this scenario, revealing that the observed magnetic helicity increase is associated with the compression of turbulent structures at the shock front.

Properties of an Interplanetary Shock Observed at 0.07 and 0.7 au by Parker Solar Probe and Solar Orbiter

“…A crucial feature found for the energetic particle population is the fluctuations found in their fluxes immediately downstream of the shock, with typical timescales of 1-2 minutes, particularly evident for the lower-energy channels (0.05-0.35 MeV, shown in dark blue to green). Such fluctuations correlate well with the magnetic field structuring (Figures 7(a), (b), and (c)), thus suggesting that particle acceleration is indeed happening in an irregular fashion for this IP shock, where additional acceleration may be provided by the magnetic structures (Zhao et al 2018;Nakanotani et al 2021;Trotta et al 2022b). To quantify the variability associated with the shock crossing, the θ Bn and local θ BR angles have been estimated using the local magnetic field, the radial direction, and the average shock normal, as reported in Table 1.…”

Rankine–Hugoniot Relations and Magnetic Field Enhancement in Turbulent Shocks

“…It has been found observationally on the Earth's bow shock that very long waves with a period of tens of seconds pass from the foreshock and propagate in the magnetosheath toward the magnetopause (Turc et al 2023). Recent simulations show enhancement of the turbulence on transmission through the shock (Trotta et al 2021(Trotta et al , 2022(Trotta et al , 2023. In these simulations, there is a preexisting turbulence with amplitudes higher than those observed and wavelengths much smaller than those observed.…”

Irregular Proton Injection to High Energies at Interplanetary Shocks

“…The hybrid kinetic simulations are consistent with this complex scenario of proton acceleration, with irregularly distributed suprathermal particles along the shock front, an invaluable tool to elucidate the small-scale behavior of this IP shock and of shock transitions in a variety of astrophysical systems. Our model highlights the very small-scale behavior of the shock but neglects other effects like preexisting turbulence and IP disturbances that may be important (Lario & Decker 2002;Trotta et al 2022b;Nakanotani et al 2022;Trotta et al 2023b). The direct investigation of shock acceleration in systems other than the Earth's bow shock (having a small radius of curvature and many other properties important for planetary bow shocks) is important to build a comprehensive understanding of collisionless shocks energetics.…”