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Electric fields associated with small‐scale magnetic holes in the plasma sheet: Evidence for electron currents
Author(s) -
Goodrich Katherine A.,
Ergun Robert E.,
Stawarz Julia E.
Publication year - 2016
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1002/2016gl069601
Subject(s) - gyroradius , current sheet , magnetic field , physics , plasma sheet , magnetohydrodynamics , electron , plasma , electric current , current (fluid) , magnetohydrodynamic drive , electric field , ion , radius , pressure gradient , boundary layer , atomic physics , magnetosphere , mechanics , quantum mechanics , computer security , computer science , thermodynamics
We report observations of magnetic holes (MHs) in the near‐Earth (8 R E to 12 R E ) plasma sheet that have physical sizes perpendicular to the magnetic field ( B ) on the order of the ion Larmor radius ( ρ i ) and, more importantly, have current layers less than ρ i in thickness. Small‐scale MHs can have >90% depletion in | B | and are commonly associated with the braking of bursty bulk flow events. The generation of MHs is often attributed to magnetohydrodynamic (MHD) instabilities, which requires a size greater than ρ i ; the depletion in | B | is from an ion current consistent with a pressure gradient. Electric field ( E ) observations indicate a negative potential inside of small‐scale MHs that creates an outward E at the boundary, which drives an E × B electron current in a thin layer. These observations indicate that a Hall electron current is primarily responsible for the depletion of | B | in small‐scale magnetic holes, rather than the ion pressure gradient.