Effect of ionosphere and inhomogeneity of the Earth structure on the polarization characteristics of magnetic field at frequencies of 0.2–200 Hz in the near-field zone of a horizontal grounded antenna

Polarization characteristics of the field of an on-Earth emitter located at the Kola Peninsula are experimentally measured at a distance that is no greater than the height of an effective ionospheric waveguide in the FENICS-2014 experiment. Variations in the field amplitude and orientation of the major axis of polarization ellipse are observed at lower frequencies upon significant changes of the K index of geomagnetic activity. Polarization characteristics of the horizontal component of magnetic field calculated with allowance for the ionosphere and two-layer Earth structure prove the observed sensitivity of the ultralow- and lower-frequency filed in the near-field zone to the state of ionosphere at lower conductivity of underlying medium. Theoretical results are compared with the experimental data. The results are important for deep sounding of the Earth and monitoring of ionosphere with the aid of controlled low-frequency ground sources.