Kinetics of sub-ion scale magnetic holes in the near-Earth plasma sheet

In collisionless space plasmas, the energy cascade from larger to smaller scales requires effective interactions between ions and electrons. These interactions are organized by sub-ion scale plasma structures in which strong electric fields connect demagnetized ions to magnetized electrons. We consider one such structure, magnetic holes, observed by THEMIS spacecraft in the dipolarized hot plasma sheet. Magnetic holes are localized depressions of the magnetic field with strong currents at their boundaries. Taking advantage of slow plasma convection (∼10 − 20 km/s), we reconstruct the electron velocity distribution within magnetic holes and demonstrate that the current at their boundaries is predominantly carried by magnetized thermal electrons. The motion of these electrons is the combination of diamagnetic drift and E × B drift in a Hall electric field. Magnetic holes can effectively modulate the intensity of electron cyclotron harmonic (ECH) waves, and thus the spatial distribution of thermal electron precipitation. They may also contain field-aligned currents with magnitudes of ∼5 nA/m2(one order of magnitude smaller than the cross-field current density). Therefore, sub-ion scale magnetic holes can be important for ionosphere-magnetosphere coupling.

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