Motion of Current Systems in the Ionosphere

Abstract

THEORETICAL studies of the behaviour of electric current systems in the lower ionosphere, treated as a rigid anisotropic shell, indicate that the Hall-current conductivity produces a rotation of these systems from west to east about the geomagnetic axis. When a given current system is expressed in terms of spherical harmonics, it is found that the components of the system corresponding to harmonics of different order n rotate with different speeds, because the angular velocity contains a factor (2n + 1)/(n² + n) (refs. 1 and 2). It follows that the pattern of the current system is distorted as it rotates, but the rate of distortion may be fairly slow if only a few close values of n are involved. Using the conductivity tensor adopted by Ferris and Price, the corresponding velocities of the current pattern at latitude λ range from 8.3 × 10⁶ sin λ cm/sec for n = 1 to 1.06 × 10⁶ sin λ cm/sec for n = 10.