Turbulence-driven Anisotropic Acceleration of Energetic Electrons in Solar Wind Current Sheets

Coherent structures in the solar wind, such as current sheets, are widely recognized as potential sites for energy dissipation and particle acceleration. However, the mechanisms driving energetic electron acceleration within these structures, particularly the role of embedded turbulence, remain observationally unconstrained. In this Letter, we present a statistical analysis of 103 mesoscale current sheet events observed by the WIND spacecraft. Our results reveal modest enhancements in energetic electron fluxes (40–310 keV) within these structures. More notably, the acceleration exhibits a pronounced anisotropy, with a preferential energization in the perpendicular direction. Further analyses indicate that this anisotropic energization is strongly modulated by the local turbulence. The perpendicular energy spectrum systematically hardens with increasing intermittency and with higher values of the local energy transfer rate. These findings are consistent with a turbulence-driven, second-order Fermi-like process, where acceleration efficiency is enhanced when the interaction scale permits quasi-adiabatic scattering. The observed perpendicular energization appears closely linked to the compressive, intermittent structures frequently generated within the current sheets. The subtle nature of the observed signatures also provides an explanation for the historical scarcity of definitive evidence for energetic electron acceleration in solar wind current sheets. By establishing the first systematic observational connection between anisotropic acceleration signatures and scale-dependent turbulence diagnostics, this study might provide a critical step toward bridging theoretical models and in situ observations of energetic electron acceleration in the heliosphere.