Validation of single spacecraft methods for collisionless shock velocity estimation

Abstract

The velocity of a collisionless shock (CS) is an important parameter in the determination of the spatial scales of the shock. The spatial scales of the shock determine the processes that guide the energy dissipation, which is related to the nature of the shock. During the pre‐ISEE era, estimations of relative shock‐spacecraft velocity (VSh) were based on spatial scales of the shock front regions, in particularly the foot. Multispacecraft missions allow more reliable identification of VSh. The main objective of this study is to examine the accuracy of two single spacecraft methods, which use the foot region of quasi‐perpendicular shocks in order determine VSh. This is important for observational shock studies based on a single spacecraft data such as Venus Express (VEX) and THOR, a proposed single spacecraft mission of European Space Agency. It is shown that neither method provides estimates with an accuracy comparable to multipoint measurements of VSh. In the absence of alternative techniques to identify the VSh and therefore the spatial scales of the shocks, the methods can be used to provided order of magnitude estimations for the spatial scales of the shock front. Observations of the Venusian bow shock from VEX data have been used as an illustrative example for the application of these methods to estimate the shock spatial scale and the corresponding errors of this estimation. It is shown that the spatial width of the ramp of the observed shock is L ∼ 3.4 ± 1.4c/ωpe.

The Structure of the Martian Quasi‐Perpendicular Supercritical Shock as Seen by MAVEN

“…It is also in agreement with Giagkiozis et al. (2017), who measured a ramp for a Venusian shock. The clean monotonic jump we observed would fall under Newbury et al.…”

“…The observed ramp width agrees with Earth studies by Mazelle et al (2010), falling under their reported most probable values with ramp thicknesses below 5 c pe / , as well as several thin shocks reported by Hobara et al (2010) with ramps below 4 c pe / . It is also in agreement with Giagkiozis et al (2017), who measured a ( .…”

“…/  c pi  that suggested the dominance of ion kinetics in energy dissipation processes in the highly supercritical Kronian bow shock. Other works include Giagkiozis et al (2017) measurement of ramp widths of ∼3 c pe / for the Venusian shock, or Moses et al (1985) analysis of electron heating generated by ion reflection at the foot of the Jovian shock.…”

Laboratory evidence for proton energization by collisionless shock surfing

“…In contrast, when the B-field is switched off, only a smooth plasma expansion into the ambient (blue dashed line) can be seen. In the case when the magnetic field is applied, another clear signature of the magnetized shock, observed by satellite 27 , is the noticeable feature of a "foot" in the density profile, located in the shock upstream (US). It is due to the cyclic evolution of the plasma: the plasma in the foot is picked up to form the shock front, while the latter is also periodically dismantled by the Larmor.…”

Detailed characterization of laboratory magnetized super-critical collisionless shock and of the associated proton energization

“…The piston front is steepened by the compression of the magnetic field (see also below). Besides, we can clearly see a "foot" structure ahead of the shock front in the upstream (US) region for the case with both ambient gas and B-field, indicating the formation of the magnetized shock 47 .…”