Transmission of a Magnetospheric Pc1 Wave Beam Through the Ionosphere to the Ground

Abstract

AbstractA characteristic feature of the upper ionosphere is the occurrence of the ionospheric Alfvén resonator (IAR) and the ionospheric fast‐mode waveguide (IFW), which can trap electromagnetic wave energy in the Pc1 frequency range from fractions of a hertz to a few hertz. This wave trapping ensures the dependence of ionospheric transmission/reflective properties on frequency. We numerically model magnetospheric Alfvén wave transmission through the ionosphere to the ground based on solution of the magnetohydrodynamic full‐wave equations in a realistic ionosphere, whose parameters are reconstructed from the International Reference Ionosphere model. The spatial structure of an incident wave is modeled as a localized beam with a finite latitudinal scale λ⊥ and an azimuthally propagating wave. The IAR and IFW modes are coupled owing to the Hall conductivity and geomagnetic field inclination. Ground spatial and spectral structures of the Pc1 wave (0.1‐ to 6‐Hz band) have been calculated for summer day/night conditions at the Antarctic Halley observatory, though results may be qualitatively applied to any midlatitude site. An incident wave with azimuthal wave vector ky=1.7·10−3 km−1, and λ⊥=102 km has been considered. The model predicts that beneath the incident beam the ground magnetic response “duplicates” its structure after accounting for a π/2 rotation and some latitudinal shift/widening. The transmission has an oscillatory dependence on frequency, thus forming “transmission windows” at resonant frequencies of IAR and IFW modes. The spectra vary depending on distance from an incidence point. Interference between IFW modes is revealed in the nonmonotonic and frequency‐dependent character of latitudinal variations of wave amplitude.