Theoretical models of ionospheric electrodynamics and plasma transport

Abstract

A relationship between J, the current density, and E′, the electric field measured in the frame of the neutral wind, is derived for a planetary ionosphere: J = Q + E′. If pressure gradients and gravity are neglected, this reduces to the well‐known J = E′, where is the conductivity tensor. If J = 0, this reduces to ambipolar diffusion. Neither J = E′ nor ambipolar diffusion can describe the vertical motion of plasma in a dynamo region, a region where electrons are tied to fieldlines, but ions are not. This has prevented models from accurately describing how vertical plasma transport affects plasma densities in the martian ionosphere. The relationship J = Q + E′ is applied to a one‐dimensional ionospheric model to study ion velocities, electron velocities, currents, electric fields, and induced magnetic fields simultaneously and self‐consistently. In this model, ion and electron velocities transition smoothly from moving across fieldlines below the dynamo region to moving along fieldlines above the dynamo region. This relationship is valid for the terrestrial ionosphere; replacing J = E′ with J = Q + E′ in terrestrial models may alter some of their predictions.