Power line harmonic radiation observed by the Kannuslehto station and the DEMETER spacecraft

Properties of power line harmonic radiation (PLHR), electromagnetic radiation produced by electric power networks, are examined. Particularly, we study how PLHR intensity depends on local time and geomagnetic activity and what are its characteristic spatial scales. We use high-resolution wave data measured by the ground-based Kannuslehto station in northern Finland, supplemented with corresponding conjugate measurements from the low-altitude DEMETER spacecraft. PLHR intensities are calculated by subtracting the background wave intensities at nearby frequencies (+/- 2 Hz). The effects of geomagnetic activity on PLHR are associated with geomagnetically induced currents (GICs) that are created at the Earth’s surface by the space weather-related events and that influence the creation of PLHR directly in the power grids. We characterize the strength of GICs using the change of the horizontal component of the geomagnetic field measured by magnetometers (IMAGE magnetometer network) located close to the Kannuslehto station. We show that PLHR is continuously detected by Kannuslehto, being more intense at odd harmonics during the day and during periods of large magnetic field changes. Data from the DEMETER spacecraft are used for selected PLHR events to estimate their characteristic spatial scales.