The Foreshock

Abstract

Although collisionless shocks primarily exist to mediate the flow of supermagnetosonic plasma, they also act as sites for particle acceleration. It is now well known that for certain magnetic field geometries, a portion of the inflowing plasma returns to the upstream region rather than being processed by the shock and passing irreversibly downstream. The combination of the inflowing plasma and this counterstreaming component upstream of the shock is subject to a number of plasma instabilities, leading to the generation of waves. These waves interact in a highly complex manner with the ions and electrons making up the plasma and can cause part of the plasma distribution to reach high energies.The region of space upstream of the bow shock, magnetically connected to the shock and filled with particles backstreaming from the shock is known as the foreshock. As discussed in Balogh et al. (2005), the bow shock can be classified into quasi-perpendicular and quasi-parallel shock regions according to the angle θ Bn between the shock normal n and the direction of the solar wind magnetic field B. For the quasi-perpendicular bow shock (θ Bn > 45 • ), the foreshock is restricted to the shock foot, while in the quasi-parallel part of the bow shock (θ Bn < 45 • ), it

Magnetic field and dynamic pressure ULF fluctuations in coronal-mass-ejection-driven sheath regions

“…Thus, it is expected that turbulent characteristics of the ICME sheath and embedded ULF fluctuations are also modified when the sheath interacts with the bow shock. The interaction begins already in the foreshock region, where a large variety of different plasma waves exist (e.g., Eastwood et al, 2005). It is also possible that part of the ULF fluctuations that eventually hit the magnetopause are generated by local sources in the foreshock and bow shock downstream regions (see e.g., Gutysnka et al, 2012;Hartinger et al, 2012, and references therein).…”

On the edge of the foreshock: model-data comparisons

“…Ion foreshock intervals can be identified on the basis of correlated 30 s period density and magnetic field strength fluctuations and suprathermal (>1 keV) ion fluxes (Fairfield et al, 1990;Eastwood et al, 2006). Based on these considerations, the observations shown in Fig.…”

Statistical study of foreshock cavitons

“…The ULF waves can appear as sinusoidal, transverse waves propagating almost parallel with respect to the upstream IMF, or they can be compressive, obliquely propagating fluctuations. The region upstream of the Earth's bow shock that is magnetically connected to it, is called the Earth's foreshock (Le and Russell, 1992a, b;Eastwood et al, 2005;Greenstadt et al, 1995).…”