Combined ground-based VLF/LF electric field and particle measurements related to solar variations in the solar cycle 25

In this study we investigate intermittent phenomena in VLF/LF electric fields and particle outbursts caused by solar activity fluctuations and affecting principally the Earth’s ionosphere. Strong events from the current solar cycle 25, e.g., x-ray flares, generate electric field amplitude and phase variations occurring on the ray-path between the VLF/LF transmitter stations and the reception facilities. These variations in the sub-ionospheric waveguide, with the lower ionosphere as upper boundary (D/E-layer during day/night), are complementary to secondary cosmic ray data measured by ground-based (muon) detectors. VLF/LF measurements are from the European INFREP receiver network and muon particle observations are collected from the Belgrade detector in Serbia. With the combined observation sets we analyze and characterize single events and corresponding statistical parameters. The study benefits from continuous ground based long-term measurements and the multi-parameter approach using complementary instrumentations.