Dr Louis Richard: Publications

Ion Anisotropy in Earth's Magnetotail: Importance of High‐Energy Ions

Journal of Geophysical Research: Space Physics American Geophysical Union (AGU) 131:6 (2026) e2026JA035223

Authors:

Xiaofei Shi, Vassilis Angelopoulos, Louis Richard, Anton Artemyev

Abstract:

Abstract The reconfiguration of the magnetotail current sheet during substorms often includes the formation of a thin current sheet (TCS) with a strong magnetic field line tension force. This force cannot be balanced by isotropic plasma pressure gradients, and force balance in such a TCS requires ion anisotropy and/or agyrotropy of plasma pressure. A statistical investigation of these plasma properties in the magnetotail is challenging because a significant contribution to ion anisotropy or agyrotropy stems from the suprathermal ion population, which often has energies beyond the upper limit of electrostatic analyzer measurements. In this study, we compare ion measurements from Cluster, MMS, and THEMIS to investigate the ion anisotropy in the magnetotail current sheet. We show that the central region of the magnetotail is characterized by transverse anisotropy of suprathermal ions, whereas subthermal field‐aligned anisotropic ions populate the magnetotail current sheet boundaries. Our results indicate that different ion populations (subthermal, thermal, and suprathermal ions) exhibit distinct behaviors within the current sheet, showing that different combinations of these populations contribute differently to the stability of current sheets.

Occurrence of Flat-top Electron Velocity Distributions in Magnetotail Plasma Jets

ArXiv 2604.05992 (2026)

Authors:

Louis Richard, Yuri V Khotyaintsev, Cecilia Norgren

Finding Local Parallel Electric Fields in Magnetotail Reconnection Using a Two‐Spacecraft Method

Geophysical Research Letters American Geophysical Union (AGU) 53:6 (2026) e2025GL119588

Authors:

JD White, Yu V Khotyaintsev, C Norgren, DB Graham, L Richard

Abstract:

Abstract We investigate the use of a novel two‐spacecraft Liouville‐mapping method using data from the Magnetospheric Multiscale mission to determine local magnetic‐field‐aligned (parallel) electric fields in the Earth's magnetotail. The method detects the presence of local acceleration potentials by mapping phase‐space density between electron velocity distribution functions from two field‐aligned spacecraft upstream and downstream of acceleration regions. Applying the method to a magnetic reconnection event, we find that local parallel electric fields near the current sheet (CS) center are, on average, directed away from the center, resulting from the need to maintain quasi‐neutrality across the CS. Despite significant measurement uncertainties, we find that the local acceleration potentials are smaller than the total acceleration potential, typically 1%–2% on average and up to 9% for individual measurements. This indicates that many potential drops, over distances much larger than the spacecraft separations, contribute to the net work done on electrons by parallel electric fields.

Statistical study of Field-Aligned Currents in the Ionosphere associated with Bursty Bulk Flows Events

(2026)

Authors:

Vanina Lanabere, Andrew P Dimmock, Adrian Blagau, Stephan Christoph Buchert, Octav Marghitu, Louis Richard

Ion temperature anisotropy limits from magnetic curvature scattering in magnetotail reconnection jets

Physics of Plasmas AIP Publishing 33:2 (2026) 022110

Authors:

Louis Richard, Anton V Artemyev, Cecilia Norgren, Xin An, Sergei R Kamaletdinov, Yuri V Khotyaintsev

Abstract:

In collisionless plasmas, relaxation of the deviations of ion velocity distribution functions (VDFs) from local thermodynamic equilibrium occurs through particle interactions with electromagnetic fields. In particular, in the Earth's magnetotail, the deviations of the ion VDFs, typically consisting of multiple components, from the equilibrium must be limited to maintain stability of the current sheet. Curvature scattering is a leading candidate mechanism to limit such deviations, but its role remains insufficiently understood. We investigate the limits of ion temperature anisotropy in a magnetotail-like configuration by modeling a quasi-1D current sheet with a finite magnetic field curvature and three ion populations. We derive analytical thresholds for anisotropy based on current sheet stability and validate against spacecraft observations and numerical simulations. Our findings demonstrate that curvature scattering imposes limits on ion anisotropies, thereby maintaining the stability of the current sheet.

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Dr Louis Richard

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Ion Anisotropy in Earth's Magnetotail: Importance of High‐Energy Ions

Authors:

Abstract:

Occurrence of Flat-top Electron Velocity Distributions in Magnetotail Plasma Jets

Authors:

Finding Local Parallel Electric Fields in Magnetotail Reconnection Using a Two‐Spacecraft Method

Authors:

Abstract:

Statistical study of Field-Aligned Currents in the Ionosphere associated with Bursty Bulk Flows Events

Authors:

Ion temperature anisotropy limits from magnetic curvature scattering in magnetotail reconnection jets

Authors:

Abstract:

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Dr Louis Richard

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Ion Anisotropy in Earth's Magnetotail: Importance of High‐Energy Ions

Authors:

Abstract:

Occurrence of Flat-top Electron Velocity Distributions in Magnetotail Plasma Jets

Authors:

Finding Local Parallel Electric Fields in Magnetotail Reconnection Using a Two‐Spacecraft Method

Authors:

Abstract:

Statistical study of Field-Aligned Currents in the Ionosphere associated with Bursty Bulk Flows Events

Authors:

Ion temperature anisotropy limits from magnetic curvature scattering in magnetotail reconnection jets

Authors:

Abstract:

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