High-Frequency Waves Associated with Collisionless Shocks

Abstract:

Collisionless shocks play a significant role in the solar wind interaction with the planets, and their studies are important for understanding of physical processes in the vicinity of astrophysical objects. The main process that takes place at the collisionless shock is the redistribution of the energy of the directed plasma motion to the plasma thermalization and acceleration of a part of particles to high energies. The shocks are often associated with high-frequency (several Hz) wave packets in both upstream and downstream regions. These waves could be resolved only in fast magnetic field data because the time resolution of plasma instruments is often insufficient for their detection. The BMSW instrument onboard the Spektr-R spacecraft measures solar wind parameters with a resolution of 32 ms and open new ways to a detailed analysis of these waves. In this paper, we compare the waves in regions adjacent to interplanetary shocks observed in course of the 2011–2013 years and with a set of bow shock crossings associated with wave activity. Since the magnetometer onboard Spektr-R is not in operation, we compare BMSW observations with Wind fast magnetic field measurements. We analyze differences in the ion structure of low-Mach number fast forward interplanetary shocks and bow shocks (as representatives of fast reverse high-Mach number shocks). The comparison is focused on the formation mechanism of both types of shocks and on a search for a best scaling parameter.