Simulations of ELF radiation generated by heating the high‐latitude D region

Abstract

Three‐dimensional simulations show the ELF (extremely low frequency) radiation generated by heating the high‐latitude D region and modulating the polar electrojet The simulations use a time‐varying current perturbation in the D region. The ELF radiation is calculated in the Earth‐ionospheric waveguide to a radial distance of 2400 km. The angular and radial dependence and the polarization of the horizontal, ground‐level magnetic field are determined. The radiation pattern is a combination of a linear dipole antenna and a right‐hand circular antenna. At ELF frequencies because of low D region absorption the dipole is dominant. The polarization and field strength in the near‐field can predict the orientation of the radiation pattern and the wave amplitude in the far‐field. The near‐field polarization indicates the direction and strength of the electrojet. As the electromagnetic wave propagates in the waveguide, it drives whistlers waves into the D region. Because of reflection from the D region the mode inside the waveguide is not purely transverse. This gives a counterclockwise rotation to the polarization. Directly above the heated region, waves are also launched along the Earth's magnetic field. The near‐field polarization shows good agreement with observations from the high‐power auroral stimulation array (HIPAS) and Tromsø.