Multispacecraft Analysis of Electron Holes

Abstract

Abstract Electron holes (EHs) are nonlinear electrostatic structures in plasmas. Most previous in situ studies of EHs have been limited to single‐ and two‐spacecraft methods. We present statistics of EHs observed by Magnetospheric Multiscale on the magnetospheric side of the magnetopause during October 2016 when the spacecraft separation was around 6 km. Each EH is observed by all four spacecraft, allowing EH properties to be determined with unprecedented accuracy. We find that the parallel length scale, l ∥ , scales with the Debye length. The EHs can be separated into three groups of speed and potential based on their coupling to ions. We present a method for calculating the perpendicular length scale, l ⊥ . The method can be applied to a small subset of the observed EHs for which we find shapes ranging from almost spherical to more oblate. For the remaining EHs we use statistical arguments to find l ⊥ / l ∥ ≈5, implying dominance of oblate EHs.