Ground-Based PWING Observations of Power Line Harmonic Radiation in Finland During Geomagnetic Disturbances: Initial Results

Power line harmonic radiation (PLHR) is an important anthropogenic source of electromagnetic waves generated by power networks. It appears at harmonic frequencies of the fundamental power grid frequency, and these harmonics can reach up to several thousand Hz. In this study, we analyse PLHR using wave measurements from the ground-based PWING network. This study primarily focuses on measurements conducted in northern Finland, specifically at Angeli (69.02°N, 25.82°E), Kannuslehto (67.74°N, 26.27°E), and Oulujarvi (64.51°N, 27.23°E). Wave intensity data with a high frequency resolution (1 Hz) are used to investigate the properties of PLHR from 50 Hz up to 1000 Hz, particularly its dependence on geomagnetically induced currents (GICs) associated with space weather events. The wave data are complemented by nearby 1 s magnetometer measurements from the Finnish IMAGE network stations, which are used to estimate GIC strength via the temporal variation of the horizontal magnetic field component (dB/dt). Preliminary results for geomagnetic storms of October 2024 and January 2025 indicate that the intensity of PLHR is significantly enhanced by an order of magnitude during geomagnetic active times, particularly for even harmonics at 300 Hz, 600 Hz, and 900 Hz, which are usually weak or absent in well-operating power systems and appear mostly when the current waveform gets distorted. We also investigate a possible delay between GIC events and the resulting distortion of the current waveforms, and discuss the implications for the required time resolution of magnetometer data.