English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Tools annual

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools monthly

Global: Zendy Plus monthly

Presents the access of premium content as premium feature

Premium Content

Global: Zendy Plus annual

Global: Zendy Free Plan

Abstract. The nonstationarity of the terrestrial bow shock is analyzed indetail from in situ magnetic field measurements issued from the fluxgate magnetometer (FGM)experiment of the Cluster mission. Attention is focused on statisticalanalysis of quasi-perpendicular supercritical shock crossings. The presentanalysis stresses for the first time the importance of a careful andaccurate methodology in the data processing, which can be a source ofconfusion and misunderstanding if not treated properly. The analysis performedusing 96 shock front crossings shows evidence of a strong variability of themicrostructures of the shock front (foot and ramp), which are analyzed ingreat detail. The main results are that (i) most statistics clearly show that theramp thickness is very narrow and can be as low as a few c/ωpe(electron inertia length); (ii) the width is narrower when the angleθBn (between the shock normal and the upstream magnetic field)approaches 90∘; (iii) the foot thickness strongly varies, but itsvariation has an upper limit provided by theoretical estimates given inprevious studies (e.g., Schwartz et al., 1983; Gosling and Thomsen, 1985;Gosling and Robson, 1985); and (iv) the presence of foot and overshoot, as shownin all front profiles, confirms the importance of dissipative effects.Present results indicate that these features can be signatures of the shockfront self-reformation among a few mechanisms of nonstationarity identifiedfrom numerical simulation and theoretical studies. A comparison with 2D particle-in-cell (PIC) simulation for a perpendicular supercritical shock(used as reference) has been performed and shows the following: (a) the rampthickness varies only slightly in time over a large fraction of thereformation cycle and reaches a lower-bound value on the order of a fewelectron inertial length; (b) in contrast, the foot width strongly variesduring a self-reformation cycle but always stays lower than an upper-bound value in agreement with the value given by Woods (1971); and (c) as aconsequence, the time variability of the whole shock front is depending onboth ramp and foot variations. Moreover, a detailed comparative analysis shows that many elements ofanalysis were missing in previous reported studies concerning both (i) theimportant criteria used in the data selection and (ii) the different andcareful steps of the methodology used in the data processing itself. Theabsence of these precise elements of analysis makes the comparison withthe present work difficult; worse, it makes some final results and conclusivestatements quite questionable at the present time. At least, looking for aprecise estimate of the shock transition thickness presents nowadays arestricted interest, since recent results show that the terrestrial shock israther nonstationary, and one unique typical spatial scaling of themicrostructures of the front (ramp, foot) must be replaced by some“variation ranges” (with lower-bound and upper-bound values) within which thespatial scales of the fine structures can extend.

annales geophysicae

Evidence of the nonstationarity of the terrestrial bow shock from multi-spacecraft observations: methodology, results, and quantitative comparison with particle-in-cell (PIC) simulations