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Conference papers

Cross-Shock Potential in Rippled vs. Planar Quasi-Perpendicular Shocks Observed with MMS

Abstract : The unprecedented high detail of field and plasma measurements by the four MMS spacecraft allows investigation of the cross-shock electric potential and related plasma dynamics in shock crossings, as well as validation of different techniques used and appropriate proxies for indirect estimation of the potential. The current study compares two quasi-perpendicular shocks observed by MMS: a terrestrial bow shock (with moderate Mach number, reflected ions, and a rippled front) and an interplanetary shock (with low Mach number, no reflected ions, and a planar front). For each shock, we have calculated the cross-shock potential by integrating either the measured electric field across the shock or a reconstruction of it under certain assumptions.

The cross-shock potential of the bow shock crossing was found to be about 350-400 V in the Normal Incidence (NI) frame, which is confirmed by the energy threshold of the reflected ion population. Comparing the measured potential to proxies obtained from ion and electron moments and the magnetic field, we find that contamination by reflected ions spoils the upstream values of proxies dependent upon ion moments, whereas proxies based on electron moments yield reasonable potential estimates upstream but are invalid downstream. The estimates of the shock normal from Maximum Variance Analysis on the electric field data indicate that the surface of the shock front is rippled rather than planar. This leads to differing potential values in the NI frame for different satellites.

The cross-shock potential of the interplanetary shock was found to be about 25-30 V in the NI frame. While there were no reflected ions to impair the potential proxies, comparison of the measured and proxy potentials was difficult because the shock speed is much higher, with the ramp observation lasting about 0.1s, close to the data rate of the ion moments. Shock normals obtained using minimum variance analysis of the magnetic field data for each spacecraft and timing analysis of data from all four spacecraft agreed to within ten degrees, indicating a planar shock front.

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https://hal-insu.archives-ouvertes.fr/insu-03565543
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Submitted on : Friday, February 11, 2022 - 8:59:27 AM
Last modification on : Tuesday, May 10, 2022 - 3:24:58 PM

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E. Hanson, O. V. Agapitov, F. Mozer, V. Krasnoselskikh, S. D. Bale, et al.. Cross-Shock Potential in Rippled vs. Planar Quasi-Perpendicular Shocks Observed with MMS. American Geophysical Union, 2018, San Francisco, United States. pp. 10. ⟨insu-03565543⟩

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