2/3/2017 - Kinetics of sub-ion scale magnetic holes in the near-Earth plasma sheet

Information:

3:30 PM - 4:30 PM
Geology 6704

Presented By:
Xiaojia Zhang - AOS/EPSS

Abstract

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 an effective interaction between ions and electrons. These interactions are organized by sub-ion scale kinetic plasma structures, where strong electric fields connect the decoupling motion of demagnetized ions and magnetized electrons. In this study, we consider one such example of sub-ion scale kinetic structures – magnetic holes, observed by THEMIS spacecraft in the dipolarized hot plasma sheet. Magnetic holes represent localized depressions of the magnetic field with strong currents at the boundaries. Taking the advantage of a very slow plasma convection (~10-20 km/s), we reconstruct the electron velocity distribution within magnetic holes and demonstrate that the current at boundaries is predominantly carried by magnetized thermal electrons. The electron motion is dominated by E×B drifts in a Hall electric field. The corresponding scalar potential drop across the hole is about a fraction of the electron temperature. We also show that magnetic holes can effectively modulate the intensity of electron cyclotron harmonic (ECH) waves, and thus modulate the spatial distribution of hot electron precipitations. The configuration of magnetic holes contains field-aligned currents with amplitudes of ~ 5 nA/m2 (one order of magnitude smaller than the amplitude of Hall current density). Therefore, these sub-ion scale magnetic holes can be important for ionosphere-magnetosphere coupling.

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