Ionospheric radio-frequency wave modeling using a finite element method analysis environment Petra-M code

We present applications of the 3D full-wave solver, Petra-M code, for ionospheric radio-frequency plasma wave physics. The Petra-M (Physics Equation Translator for MFEM) is an integrated multi-physics finite element method (FEM) analysis environment based on the MFEM module and is developed to model radio-frequency (RF) plasma wave propagation in the laboratory plasma machines, such as tokamaks. One of the advantages of the FEM simulation code is that the boundary shapes, plasma density profiles, and magnetic field configurations are easily adapted; therefore, the Petra-M has also been applied to Earth's dipole, compressed, and stretched magnetic field topologies, as well as tokamak machine geometry. In this study, we adopt a spherical geometry around the Earth and the international ionosphere reference into the Petra-M model, then focus on ionospheric RF waves, such as medium frequency (MF) bursts and auroral kilometric radiation (AKR). To examine those waves, we limit the simulation domain near the polar region and adopt fine meshes to examine short wavelength electromagnetic waves. The auroral MF bursts, left-hand polarized and wideband radio emissions, are believed to be generated in the topside ionosphere as Z-mode waves and observed at ground level during substorm onsets. The AKR generated by the electron cyclotron-maser instability near the ionospheric density cavity also leaks to low altitudes ionosphere. Since the Z-mode waves in the topside ionosphere cannot penetrate the F-region, a linear mode-conversion process between incoming Z-mode and freely propagating EM radiation is critical for wave propagation to the ground. We launch the MF or AKR waves in the topside or mid-ionosphere and perform the wave simulation in the ionosphere including linear mode conversion process.