Observation of the terrestrial bow shock in quasi‐electrostatic subshock regime

Abstract

[1] Electric field measurements made on board the four Cluster II satellites are used to estimate the spatial scale of the electrostatic potential in the front of the terrestrial bow shock in the quasi-perpendicular regime. High-amplitude electric fields (up to 70 mV m À1 ) were measured at the shock fronts encountered on 31 March 2001. The main change in the cross-shock potential took place on spatial scales of a few electron inertial lengths. Such small scales in the electrostatic potential can be explained in the framework of the quasi-electrostatic subshock concept. The high magnitude of the upstream magnetic field, which resulted in an unusually small b and moderate Mach numbers, created favorable conditions for the occurrence of quasi-electrostatic subshocks in the shock front.

Electric field scales at quasi-perpendicular shocks

“…Ion sound sub-shocks have been observed in laboratory plasmas with scales of ≈100 Debye lengths. For the shocks observed on 31 March 2001, the observed shock scale is closer to to characteristic scale of the fast magnetosonic mode (Balikhin et al, 2002).…”

“…The high value of the field resulted in an unusually small β≈0.07. The Alfvén Mach number for this shock (M a ≈3.6) lies close to the First and Second Critical Mach numbers and therefore the state of the solar wind would lead to favourable conditions for the formation of quasi-electrostatic sub-shocks at the shock front (Balikhin et al, 2002). Alfvénic Mach numbers are quoted rather than Magnetosonic Mach numbers, as it is felt that the Alfvén Mach number was more trustworthy.…”

“…Several different points of view have been published on the relationship between the scale size of the magnetic ramp and that over which the change in potential is observed. Some studies (Eselevich et al, 1971;Balikhin et al, 1993;Formisano and Torbert, 1982;Formisano, 1982Formisano, , 1985Balikhin et al, 2002;Krasnosel'skikh, 1985;Leroy et al, 1982;Liewer et al, 1991;Scholer et al, 2003) have proposed that the spatial scale of electrostatic potential is of the same order or smaller than that of the magnetic ramp under some conditions. Such shocks have been observed in numerous experimental and numerical studies of quasi-perpendicular supercritical shocks.…”

Spatial scales of the magnetic ramp at the Venusian bow shock

“…Typically the magnetic transition across the collision-less shock is the most commonly studied due to the reliability and availability of magnetic field measurements. As a result, the magnetic profile of the collision-less shock has been comprehensively studied in the space environment (Scudder et al, 1986;Farris et al, 1991;Krasnoselskikh et al, 1991;Newbury and Russell, 1996;Balikhin et al, 2002;Bale et al, 2005). Numerical simulations such as those by performed by Leroy et al (1982) have also played a critical role in our knowledge of shock structure.…”

Non-adiabatic electron behaviour due to short-scale electric field structures at collisionless shock waves

“…It is common that both scales have the same order of magnitude in simulations and observations (Balikhin et al, 1993(Balikhin et al, , 2002Formisano and Torbert, 1982;Formisano, 1982;Leroy et al, 1982;Liewer et al, 1991;Scholer et al, V. See, R. F. Cameron & S. J. Schwartz: Electron behaviour due to sho (5) - (7)). The shock width is set by the parameter D B with the D B = D E = 1 case illustrated in the figure.…”