Dr Louis Richard: Publications

Mapping and Characterizing Parallel Electric Field Structures During a Magnetotail Reconnection Event

(2026)

Authors:

Jack White, Yuri V Khotyaintsev, Daniel Bruce Graham, Konrad Steinvall, Cecilia Norgren, Louis Richard

More details from the publisher

Rapid Magnetotail Reconfiguration and Ion‐Scale Wave Activity at Mercury

Journal of Geophysical Research: Space Physics American Geophysical Union (AGU) 131:9 (2026) e2026JA035864

Authors:

M Persson, RM Dewey, AI Eriksson, M André, E Yordanova, L Richard, A Dagore, J‐E Wahlund

Abstract:

Abstract Mercury's magnetosphere is an extremely dynamic environment, where substorm‐like activity, including dipolarization fronts and particle acceleration, periodically disrupts the stability and radial extent of the closed field line region. The common narrowband ∼1 Hz waves at Mercury, near the local proton gyrofrequency are preferentially observed on closed field lines during quieter intervals, but their relationship to magnetospheric dynamics remains poorly understood. Here, we combine MESSENGER data sets of ∼1 Hz wave activity and dipolarization fronts to investigate whether newly closed field lines can sustain wave growth. We find that ∼1 Hz waves on the nightside are systematically absent during orbits with dipolarization intervals and typically confined within 1.3 R M , compared to greater downtail extents during quiet intervals. The results indicate that ∼1 Hz waves require long‐lived, stable closed field lines to grow; therefore, when they are observed, they can serve as diagnostics of Mercury's magnetospheric state, establishing a clear connection between field‐line history, magnetospheric dynamics, and wave occurrence in Mercury's magnetotail.

More details from the publisher

More details

Statistical Study of Betatron and Fermi Electron Acceleration at Dipolarization Fronts

Geophysical Research Letters American Geophysical Union (AGU) 53:15 (2026) e2026GL122885

Authors:

A Kolokotronis, DB Graham, Yu V Khotyaintsev, C Norgren, K Steinvall, L Richard

Abstract:

Abstract Magnetic reconnection jets in Earth's magnetotail are regions of electron heating and acceleration. They are often associated with dipolarization fronts (DFs), which are characterized by sharp increases in the northward magnetic field component . Electrons can be accelerated at DFs mainly through the betatron and Fermi mechanisms. We perform a statistical study of betatron and Fermi electron rate of energy change at Earthward‐propagating DFs observed by the Magnetospheric Multiscale (MMS) spacecraft. Our results show that betatron acceleration is dominant ahead of DFs, where suprathermal electron fluxes perpendicular to the magnetic field are detected. Up to ion inertial lengths inside the outflow, Fermi acceleration acts on the low‐density electron population, potentially driving them to high energies (∼100 ). Spatially in the magnetotail, betatron acceleration is statistically larger near the most probable X‐line location, while Fermi‐dominated events are observed closer to the Earth.

More details from the publisher

More details

Occurrence of Flat‐Top Electron Velocity Distributions in Magnetotail Plasma Jets

Geophysical Research Letters American Geophysical Union (AGU) 53:12 (2026) e2026GL123161

Authors:

L Richard, Yu V Khotyaintsev, C Norgren

Abstract:

Abstract Non‐Maxwellian electron velocity distributions (eVDFs) are ubiquitous in collisionless plasmas. For example, various types of non‐Maxwellian eVDFs exist in magnetic reconnection jets in the Earth's magnetotail. At thermal energies, eVDF can be flat‐topped due to electron trapping associated with magnetic reconnection. However, the occurrence of such eVDFs in magnetotail reconnection remains largely unconstrained. Here, we statistically investigate flat‐top eVDFs in fast plasma jets in the magnetotail using a new method for classifying eVDFs. We show that at least of the eVDFs in the jets are flat‐tops. In addition, we find that most jets exhibit flat‐top eVDFs, indicating that this signature of parallel acceleration and electron streaming is characteristic of the jets. We find that these flat‐top eVDFs are localized within an ion‐inertial‐length‐scale region near the edges of the current sheet and the ion diffusion region. Our results highlight the importance of flat‐top eVDFs in non‐local thermodynamic equilibrium collisionless plasmas.

More details from the publisher

More details

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.

More details from the publisher

Dr Louis Richard

Research theme

Sub department

Mapping and Characterizing Parallel Electric Field Structures During a Magnetotail Reconnection Event

Authors:

Rapid Magnetotail Reconfiguration and Ion‐Scale Wave Activity at Mercury

Authors:

Abstract:

Statistical Study of Betatron and Fermi Electron Acceleration at Dipolarization Fronts

Authors:

Abstract:

Occurrence of Flat‐Top Electron Velocity Distributions in Magnetotail Plasma Jets

Authors:

Abstract:

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

Authors:

Abstract:

FIND US

CONTACT US

Dr Louis Richard

Research theme

Sub department

Research groups

Mapping and Characterizing Parallel Electric Field Structures During a Magnetotail Reconnection Event

Authors:

Rapid Magnetotail Reconfiguration and Ion‐Scale Wave Activity at Mercury

Authors:

Abstract:

Statistical Study of Betatron and Fermi Electron Acceleration at Dipolarization Fronts

Authors:

Abstract:

Occurrence of Flat‐Top Electron Velocity Distributions in Magnetotail Plasma Jets

Authors:

Abstract:

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

Authors:

Abstract: