Indirect Experimental Evidence for the Existence of Hall and Pedersen Currents in the Auroral E Region

Abstract

THE conductivity of the ionosphere can be expressed as a tensor containing three components—σ₀, σ₁ and σ₂ representing, respectively, conductivity along the magnetic field (“longitudinal”), along an applied electric field itself perpendicular to the magnetic field (“transverse” or “Pedersen”¹), and perpendicular to both the electric and magnetic fields (“Hall”^2,3). A sample computation of Hall and Pedersen conductivities based on an electron density profile taken during auroral activity⁴ is shown in Fig. 1. For a given applied electric field independent of height the resultant current is obviously a function of height and can be computed from the geometry. It now seems that afternoon radio aurorae are basically reflexions from ion acoustic waves generated by a two-stream instability set up when electrons flow through the ions with a relative velocity some factor greater than the ion acoustic speed^5–9. The auroral echoes are received only when the radial from the radar is perpendicular to the magnetic field, and most favourable circumstances occur when the electric current flows along this direction also.