First, a shock is a region where there is a relatively sudden change in pressure created when a body moves through a matter medium at a velocity greater than that of the transmission speed of pressure waves in the medium. That can be where the wave changes to supersonic, or from supersonic back to subsonic. The term sonic is typically used, even in the plasma because it originally came from investigations of the speed of sound in air, and then was generalized to gases, liquids and solids. Plasma wave velocities came later, but the name has stuck, whether or not audible "sound" is involved.
If one examines a single body moving at supersonic speed relative to its surrounding medium, note that there are always
two shockwaves. The bow shock occurs at the front or leading edge, where the medium is highly compressed and moves at supersonic speed relative to the moving body. Then the trailing shock occurs, when the body has moved on past the local volume of the medium and the medium's velocity relative to the moving body reverts to subsonic. The intensity of the shock wave decreases with distance from the moving body. This is a bulk flow situation; a proton moving through a medium of matter does not create shockwaves, although it can have near misses and collisions. It s scale is too small to have "fluid-like" interaction with a medium. If its medium is actually the "neutrino sea" or Bengt Nyman's tiny particle medium consisting of "sii", which is similar, perhaps there could be such an interaction, but we have no evidence of it, and how things work mechanically at Planckian and smaller scales is not well known except statistically.
Magnetic fields can exert pressure (i.e., force per unit area) so plasmas can have pressures involved with them that are different from thermal or physical particle collisions. Thus, the conditions are right for the Earth and its co-moving magnetosphere moving relative to the solar wind (the interplanetary medium) to set up conditions where a shock wave can be formed., both a bow shock around the "front" part of the megnetosphere, and a trailing shock which occurs aft in the "magnetotail" region of the magnetosphere.
It is being discovered that the larger analog, the heliosphere around the Sun, is not moving fast enough through the plasma interstellar medium beyond, or the density of the interstellar medium is not high enough, for a similar shock wave to form. That has come as a surprise as it counters the prevailing predictions of the scientists dealing with such questions and models.
Wal Thornhill's article on his
Holoscience site,
Electric Sun Verified, gets into this area of science in some detail. Recommended.
Jim