Penetration of ELF Currents and Electromagnetic Fields into the Off-Equatorial E-Region of the Earth's Ionosphere

Abstract

The generation of ELF (of the order of 10 Hz) currents and electromagnetic fields in the off-equatorial E-region (90-120 km) of the Earth's ionosphere and their subsequent penetration into the deeper ionospheric layers is studied theoretically and numerically. These ELF currents and fields are generated by the interaction of an electromagnetic pulse with the E-region at its lower boundary located at 90 km above the Earth's surface. The wave penetration (with a typical wavelength of the order of 10 km) of the generated ELF currents and fields into the deeper ionospheric layers up to 120 km takes place due to the dominance of the Hall conductivity over the Pederson conductivity in the region between 90-120 km and penetration becomes diffusive above 120 km. During night time, the increase in the wave speed due to the reduced conductivities leads to the deeper penetration. As the angle between Earth's magnetic field and horizontal is increased (going away from the equator), the currents and fields penetrate deeper into the ionospheric layers with increased wavelength, the magnitudes of horizontal (east-west) and vertical currents decrease near the boundary and the vertical electric field decreases drastically. The horizontal (east-west) current integrated along vertical is fitted with a current distribution which can be replaced by a line current raised above its actual height by the half width of the current distribution for the purpose of the calculation of its radiation. The maximum of the total east-west current (310 Amps) remains same for various simulation parameters due to the magnetic shielding.