Foreshock transients upstream of Earth's bow shock have been recently observed to accelerate electrons to many times their thermal energy. How such acceleration occurs is unknown, however. Using THEMIS case studies, we examine a subset of acceleration events (31 of 247 events) in foreshock transients with cores that exhibit gradual electron energy increases accompanied by low background magnetic field strength and large-amplitude magnetic fluctuations. Using the evolution of electron distributions and the energy increase rates at multiple spacecraft, we suggest that Fermi acceleration between a converging foreshock transient's compressional boundary and the bow shock is responsible for the observed electron acceleration. We then show that a one-dimensional test particle simulation of an ideal Fermi acceleration model in fluctuating fields prescribed by the observations can reproduce the observed evolution of electron distributions, energy increase rate, and pitch-angle isotropy, providing further support for our hypothesis. Thus, Fermi acceleration is likely the principal electron acceleration mechanism in at least this subset of foreshock transient cores.
PIC simulations of nonrelativistic high-Mach-number oblique shocks propagating in a turbulent medium
University of Wisconsin-Madison（威斯康星大学麦迪逊分校）；University of Potsdam（波茨坦大学）；Deutsches Elektronen-Synchrotron DESY（德国电子同步辐射中心）；Institute of Physics of the Czech Academy of Sciences（捷克科学院物理研究所）；Max-Planck-Institut für Plasmaphysik（马克斯·普朗克等离子体物理研究所）；The University of Tokyo（东京大学）
The Wave-Regulated Precursor of a Near-Parallel Interplanetary Shock Observed by Parker Solar Probe
University of Turku（图尔库大学）；Space Sciences Laboratory, University of California, Berkeley（加州大学伯克利分校空间科学实验室）；National Taras Shevchenko University of Kyiv（基辅塔拉斯舍甫琴科国立大学）；Ben Gurion University of the Negev（内盖夫本古里安大学）；University of California, San Diego（加州大学圣地亚哥分校）；Eureka Scientific（尤里卡科学公司）；The Johns Hopkins University Applied Physics Laboratory（约翰斯·霍普金斯大学应用物理实验室）；Queen Mary University of London（伦敦大学玛丽女王学院）；KU Leuven（荷语鲁汶大学）
Multi-Mission Observations of Relativistic Electrons and High-Speed Jets Linked to Shock Generated Transients
The Johns Hopkins Applied Physics Laboratory（约翰斯·霍普金斯大学应用物理实验室）；Queen Mary University of London（伦敦大学玛丽女王学院）；University of California, Los Angeles（加州大学洛杉矶分校）；Northumbria University（诺森比亚大学）；Harbin Institute of Technology (Shenzhen)（哈尔滨工业大学（深圳））；Universidad Nacional Autónoma de México（墨西哥国立自治大学）；NASA Goddard Space Flight Center（美国国家航空航天局戈达德太空飞行中心）；University of Helsinki（赫尔辛基大学）
