Interaction of magnetospheric Alfvén waves with the ionosphere in the Pc1 frequency band

Abstract

A characteristic feature of the upper ionosphere is the occurrence of the ionospheric Alfvén resonator (IAR) and MHD waveguide, which can trap electromagnetic wave energy in the range from fractions of a Hz to a few Hz. This wave trapping ensures the strong dependence of the ionospheric transmission/reflective properties on frequency. We have developed a numerical model of the magnetospheric Alfvén wave interaction with the ionosphere and transmission to the ground based on the solution of multifluid magnetohydrodynamic (MHD) full wave equations in a realistic ionosphere, whose parameters were reconstructed from the International Reference Ionosphere model. The MHD modes are coupled owing to the frequency‐dependent Hall conductivity and geomagnetic field line inclination. This model can be applied to the interpretation of the spectral structure of electromagnetic emissions of the magnetospheric origin in the band 0.1–10 Hz observed at various latitudes. The model predicts that the upper part of the ULF spectrum (f > 1 Hz) will be severely absorbed upon wave transmission through the daytime ionosphere to the ground. At nighttime the transmission coefficient of Alfvén waves has an oscillatory dependence on frequency, with “transmission windows” at the lowest IAR eigenfrequencies (<3 Hz). At higher frequencies (3–10 Hz) the reflection/transmission coefficients are dominated by periodic scale‐dependent modulation owing to the waveguide modes. Broad maxima/minima of the transmission coefficient are determined by the phasing between Alfvén and fast magnetosonic waves at the bottom of the ionosphere.

Observation of Ionospheric Alfvén Resonances at 1–30 Hz and Their Superposition With the Schumann Resonances

“…In Figure , the 22:35–23:25 UT plot (red line) suggests that the IAR remain relatively constant in magnitude from 3 Hz to 12 Hz, once the SR is accounted for. This observation is in disagreement with much of the modeling work on IAR, which usually suggest a rapid decrease of IAR magnitude with frequency (e.g., Fedorov, Mazur, Pilipenko, & Engebretson, ; Fedorov, Mazur, Pilipenko, & Baddeley, ). However, Schekotov et al () and Fedorov, Mazur, Pilipenko, and Baddeley () suggest alternative mechanisms for IAR related to generation of fields from local lightning storms within 1,000 km.…”

“…As an interesting geophysical phenomenon, they have been extensively studied and modeled to understand their origin (e.g., Fedorov et al, ; Lysak, , ). In terms of observations, Belyaev et al () looked at the properties of IAR at high latitude ( L > 5), while Bösinger et al (, ) examined them at low latitudes ( L = 1.3).…”

Alfvén waves in the auroral region, their Poynting flux, and reflection coefficient as estimated from Swarm observations

“…These waves can be reflected at the ionosphere due to the mismatch between the Alfvén conductance and that of the ionosphere. There have been many theoretical studies on Alfvén wave reflection by the ionosphere [e.g., Knudsen et al , ; Lysak , ; Vogt , ; Fedorov et al , ]. For the simplest case of reflection we may refer to the approach of Burke et al [, and references therein], which can be summarized as follows.…”

Modulation of the ionosphere by Pc5 waves observed simultaneously by GPS/TEC and EISCAT

“…The coupled MHD equations describing these modes in an anisotropic collisional plasma can be found in Waters et al (2007) and Fedorov et al (2016). The vertical profile of local of the ionospheric parameters (conductivity tensor, Alfven velocity, electron mobility tensor, etc.)…”