Generalized Ohm’s Law Decomposition of the Electric Field in
Magnetosheath Turbulence: Magnetospheric Multiscale Observations
Abstract
Decomposing the electric field (E) into the contributions from
generalized Ohm’s law provides key insight into both nonlinear and
dissipative dynamics across the full range of scales within a plasma.
Using high-resolution, multi-spacecraft measurements of three intervals
in Earth’s magnetosheath from the Magnetospheric Multiscale mission, the
influence of the magnetohydrodynamic, Hall, electron pressure, and
electron inertia terms from Ohm’s law, as well as the impact of a finite
electron mass, on the turbulent spectrum are examined observationally
for the first time. The magnetohydrodynamic, Hall, and electron pressure
terms are the dominant contributions to over the accessible length
scales, which extend to scales smaller than the electron inertial length
at the greatest extent, with the Hall and electron pressure terms
dominating at sub-ion scales. The strength of the non-ideal electron
pressure contribution is stronger than expected from linear kinetic
Alfvén waves and a partial anti-alignment with the Hall electric field
is present, linked to the relative importance of electron diamagnetic
currents in the turbulence. The relative contribution of linear and
nonlinear electric fields scale with the turbulent fluctuation
amplitude, with nonlinear contributions playing the dominant role in
shaping for the intervals examined in this study. Overall, the sum of
the Ohm’s law terms and measured agree to within ~20%
across the observable scales. These results both confirm general
expectations about the behavior of in turbulent plasmas and highlight
features that should be explored further theoretically.