Anomalous transport effects on the parallelEfield in downward auroral current regions of the Earth's magnetosphere

Abstract

[1] The physical processes that determine the fluid quantities and the self-consistent electric field (E∥) parallel to the magnetic field have been an unresolved problem in magnetospheric physics for over 40 years. We review a recently developed kinetic and multimoment fluid theory for inhomogeneous, nonuniformly magnetized plasma with temperature anisotropy in the guiding-center and gyrotropic approximation and apply the theory to solve for the quasi steady state in the long-range potential region of a downward Birkeland current sheet when electrostatic ion cyclotron turbulence is dominant. We find that an electron, bump-on-tail-driven ion cyclotron instability produces the turbulence and that a large enhancement in ∣E∥∣ by nearly a factor of 40 occurs when the turbulence is present compared to the case when it is absent. Anomalous momentum transfer (anomalous resistivity) by itself has a very small effect on E∥; however, the presence of the turbulence and the anomalous energy transfers (anomalous heating and cooling) that result have a very large effect on the entire solution. In the electron and ion momentum balance equations for E∥, the turbulence enhances the magnitude of E∥ by reducing the effect of the generalized parallel pressure gradients and thereby enhancing the effect of the mirror forces. A new, nonlinear formula for the current-voltage relationship in downward Birkeland current regions is also given.