Solar Wind Discontinuity Transformation at the Bow Shock

Abstract

Solar wind plasma at the Earth’s orbit carries transient magnetic field structures including discontinuities. Their interaction with the Earth’s bow shock can significantly alter discontinuity configuration and stability. We investigate such an interaction for the most widespread type of solar wind discontinuities—rotational discontinuities (RDs). We use a set of in situ multispacecraft observations and perform kinetic hybrid simulations. We focus on the RD current density amplification that may lead to magnetic reconnection. We show that the amplification can be as high as two orders of magnitude and is mainly governed by three processes: the transverse magnetic field compression, global thinning of RD, and interaction of RD with low-frequency electromagnetic waves in the magnetosheath, downstream of the bow shock. The first factor is found to substantially exceed simple hydrodynamic predictions in most observed cases, the second effect has a rather moderate impact, while the third causes strong oscillations of the current density. We show that the presence of accelerated particles in the bow shock precursor highly boosts the current density amplification, making the postshock magnetic reconnection more probable. The pool of accelerated particles strongly affects the interaction of RDs with the Earth’s bow shock, as it is demonstrated by observational data analysis and hybrid code simulations. Thus, shocks should be distinguished not by the inclination angle, but rather by the presence of foreshocks populated with shock reflected particles. Plasma processes in the RD–shock interaction affect magnetic structures and turbulence in the Earth’s magnetosphere and may have implications for the processes in astrophysics.

Magnetic Discontinuities in the Solar Wind and Magnetosheath: Magnetospheric Multiscale Mission (MMS) Observations

“…Moreover, we find that the ID occurrence rate in the magnetosheath is quite lower than in the solar wind, which seems contradictory to the fact that many studies have demonstrated MHD turbulence can generate IDs, and plasmas become more turbulent crossing the bow shock (Greco et al 2008(Greco et al , 2009Borovsky 2010;Zhdankin et al 2012). One possible explanation is that the bow shock alters the IDs' stability and makes them dissipate (Kropotina et al 2021). It can also explain the two-exponential distribution of the field rotation angles of the IDs in the magnetosheath.…”

“…More recently, Liu et al (2021Liu et al ( , 2022 investigate, via the Parker Solar Probe mission (Fox et al 2016), the IDs in a previously unexplored region as close to the Sun as 0.13 au, and find an extreme abundance of RDs that may be related to the local turbulence therein and play an important role in accelerating particles in the pristine solar wind. The interaction of IDs with the terrestrial bow shock has also attracted much interest since it can significantly affect the near-Earth space environments (Koval et al 2005(Koval et al , 2006Omidi & Sibeck 2007;Samsonov et al 2007;Omidi et al 2010;Fu et al 2012a;Goncharov et al 2015;Kropotina et al 2021).…”

Asymmetric Interaction of a Solar Wind Reconnecting Current Sheet and Its Magnetic Hole With Earth's Bow Shock and Magnetopause

“…Bow shock and foreshock environments also significantly modify the current density within RDs (Kropotina et al., 2021). Crossing the bow shock can disrupt the reconnection exhausts and shut off the reconnection process within the RCS (Phan et al., 2011).…”

Magnetic Reconnection Inside Solar Wind Rotational Discontinuity During Its Interaction With the Quasi‐Perpendicular Bow Shock and Magnetosheath

“…More recently, Kropotina et al. (2021) showed that the bow shock‐RD interaction may alter the properties of the RD, which in turn makes the RD unstable to magnetic reconnection. Nevertheless, it is often hard for space observations to conclude whether reconnection has taken place inside the discontinuity before or after it touches with the bow shock.…”

“…Hamrin et al (2019) suggested that reconnection can take place at the quasi-perpendicular (Q-𝐴𝐴 ⟂ ) bow shock because of the compression of a directional discontinuity at the bow shock. More recently, Kropotina et al (2021) showed that the bow shock-RD interaction may alter the properties of the RD, which in turn makes the RD unstable to magnetic reconnection. Nevertheless, it is often hard for space observations to conclude whether reconnection has taken place inside the discontinuity before or after it touches with the bow shock.…”