Abstract
We present a systematic analysis of Power Line Harmonic Radiation (PLHR) electromagnetic wave events observed by the Van Allen Probes spacecraft over the entire duration of the mission (2012-2019). PLHR events are radiated by electric power systems on the ground at harmonics of the base power system frequency (50 or 60 Hz, depending on the region).
We analyze wave intensities at frequencies corresponding to the first few harmonics and we demonstrate that they are significantly enhanced at the times when the field-aligned magnetic footprint of the spacecraft is above industrialized areas. Considering the spacecraft locations close to the equatorial plane, this represents experimental evidence that PLHR emissions may propagate up to radial distances as large as about 4 Earth radii.
Average frequency spectra above selected industrialized regions reveal increased wave intensities at the frequencies corresponding to the first and the third harmonics, in particular during the nighttime. Multicomponent wave measurements allow us to perform a detailed wave analysis of polarization and propagation properties of the events.
The waves are typically right-handed elliptically or nearly circularly polarized, propagating with oblique wave normal angles from low latitude sources and more field-aligned wave vectors from high latitude sources. The sign of the parallel component of the Poynting flux confirms that the events indeed propagate from the anticipated ground regions.
Few events observed above the United States region propagate in the opposite direction, which is interpreted as wave bouncing between the hemispheres.