Evolution of MHD Turbulence through Shocks and a Role of the Foreshock in This Process

Abstract:

It is well established that as the solar wind expands into outer parts of our planetary system an additional heating is observed. Many mechanisms have been proposed to account for it; one of them is a dissipation of large-scale variations of solar wind parameters into the thermal energy via turbulent cascades. Shocks, including the planetary bow shocks, represent a component of the solar wind turbulence that carries a most significant portion of a free energy. Consequently, investigations of the shocks from the point of view of turbulence are of a great interest.

The BMSW instrument onboard the Spektr-R spacecraft provides a high-time resolution data (31 ms) of the ion flux, velocity, density, and temperature suitable for an analysis of the frequency spectra up to 10 Hz. Based on this high-time resolution, we analyze an evolution of the frequency spectra on MHD and kinetic scales across fast forward low-Mach number shocks as well as changes through the Earth’s bow shock representing high-Mach number reverse shocks. A role of the foreshock processes in this evolution is highlighted. We discuss the upstream and downstream plasma parameters that determine the properties of the turbulence such as spectral slopes and breaks in the frequency spectra.