Model of electromagnetic signals of Electron phase-space Holes observed by THEMIS

Strong Electron phase-space Holes (EHs) (eΦ / Te ∼> 1, where Φ is the amplitude of the potential associated with an EH, and Te is the local electron temperature) in space plasmas are of particular interest because they are likely generated by nonlinear, energetic behavior such as magnetic reconnection and strong double layers. Andersson et al. [2009, PRL] reported unusual EHs in Earth’s plasma sheet observed by THEMIS that are large in size, moving very fast, and associated with strong potentials. These characteristics of EHs are derived from the large-amplitude electric field signals δE as well as the magnetic field signals δB associated with these EHs. The perpendicular magnetic field signals δB⊥ are interpreted as being primarily from the Lorentz transformation of the BGK electric fields of EHs from the EH rest frame to the spacecraft frame, while the parallel magnetic field signals δB∥ come from the δE × B0 drift of electrons. Based on this interpretation, a model of EHs is constructed which shows that δB∥ depends on the local plasma density n0, the ambient magnetic field B0, and the shape of the EH. A statistical study of EHs supports that interpretation and shows that most EHs have perpendicular sizes a few times their parallel sizes, but some EHs likely have spherical shapes in the burst reported by Andersson et al. [2009, PRL]. Because strong EHs are likely related to nonlinear, energetic behavior in space, such as magnetic reconnection and double layers, we believe it is important to study their generation mechanism in order to reveal both their possible sources and the relation between the characteristics of strong EHs and their sources.