Publication Date:
2016-06-12
Description:
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.
Print ISSN:
0094-8276
Electronic ISSN:
1944-8007
Topics:
Geosciences
,
Physics
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