Ion Distribution Functions and Transport Properties in Collision-free Auroral Ionosphere Under Arbitrary Electric Fields

Abstract

Filamentary space-charge aurorae bring about cylindrical structures symmetric to local geomagnetic field lines in auroral ionosphere. It produces arbitrary structured electric fields. Developed from previous work on a backward mapping technique to solve ion velocities and transport properties under both collision-free and collisional conditions in cylindrically symmetric, uniformly charged auroral ionosphere, this paper studies the collision-free case by numerically solving the Boltzmann-Vlasov equation in the presence of three arbitrarily chosen electric field configurations: (1) an electric field which is proportional to the radius inside a space charge cylinder but drops off slowly outside the cylinder; (2) an electric field which is still proportional to the radius inside the space charge cylinder but drops off more quickly out side the cylinder; and, (3) an electric at the edge of the cylinder. Various shapes of non-Maxwellian ion velocity distributions and associated transport properties are obtained. In regimes where the electric field dropped outside the space-charge region, the evolving velocity distribution with time is found to have many possible types of shapes, such as, deformed pancake, horseshoe, teardrop, core-halo, etc. If the electric field drops sharply on both sides of the boundary of the region, the distribution develops into an ear-collar appearance with time. Under all electric field structures, the non-Maxwellian distributions and related transport parameters are localized to the region where the electric field permeates. The results are expected to be applicable to account for ongoing and future high-resolution observations.