On the Kinetic Theory of Subauroral Arcs

Abstract

AbstractWe report on a novel scenario of subauroral arcs within strong subauroral ion drifts (SAID)‐STEVE and Picket Fence. Their explanation requires a local source of low‐energy, ε < 18.75 eV, suprathermal electrons, and N2 vibrational and electronic excitation below ∼270 km. We show that the ionospheric feedback instability in strong SAID flows with depleted density troughs generates intense, small‐scale field‐aligned currents and parallel electric fields below the F2 peak. With these fields, we employed a rigorous numerical solution of the Boltzmann kinetic equation for the distribution of ionospheric electrons and determined the power going to excitation and ionization of neutral gas (the energy balance). The obtained suprathermal electron population and energy balance at altitudes of ∼130–140 km are just what is necessary for Picket Fence. Concerning STEVE, the kinetic theory predictions are in a good qualitative agreement with its basic features, such as the enhanced continuum emissions. Besides, the theory predicts that subauroral arcs might have the transient phase with typical aurora‐like emissions that fade out afterward.