The importance of lightning has long been recognized from the point of view of climate-related phenomena. However, the detailed investigation of lightning on global scales is currently hindered by the incomplete and spatially uneven detection efficiency of ground-based global lightning detection networks and by the restricted spatio-temporal coverage of satellite observations. We are developing different methods for investigating global lightning activity based on Schumann resonance (SR) measurements. SRs are global electromagnetic resonances of the Earth-ionosphere cavity maintained by the vertical component of lightning. Since charge separation in thunderstorms is gravity-driven, charge is typically separated vertically in thunderclouds, so every lightning flash contributes to the measured SR field. This circumstance makes SR measurements very suitable for climate-related investigations. In this study, 19 days of global lightning activity in January 2019 are analyzed based on SR intensity records from 18 SR stations and the results are compared with independent lightning observations provided by ground-based (WWLLN, GLD360 and ENTLN) and satellite-based (GLM, LIS/OTD) global lightning detection. Daily average SR intensity records from different stations exhibit strong similarity in the investigated time interval. The inferred intensity of global lightning activity varies by a factor of 2-3 on the time scale of 3-5 days which we attribute to continental-scale temperature changes related to cold air outbreaks from polar regions. While our results demonstrate that the SR phenomenon is a powerful tool to investigate global lightning, it is also clear that currently available technology limits the detailed quantitative evaluation of lightning activity on continental scales.

Pc1 pulsations cover the 0.2–5 Hz frequency range with electromagnetic ion cyclotron (EMIC) waves of magnetospheric origin being generally accepted as their most important source. In the ionosphere, the initially transverse EMIC waves can couple to the compressional mode and propagate long distances in the ionospheric waveguide. By studying the Pc1 frequency range in the topside ionosphere, we can obtain information on the spatial distribution of both the transverse (incident EMIC) waves and the compressional waves. In the present paper, we make use of a new Swarm L2 product developed for characterizing ultra low frequency Pc1 waves to explore the spatial distribution of these waves relative to the midlatitude ionospheric trough (MIT), which corresponds to the ionospheric footprint of the plasmapause (PP) at night. It is shown that the vast majority of Pc1 events are located inside the plasmasphere and that the spatial distributions clearly follow changes in the MIT/PP position at all levels of geomagnetic activity. In the topside ionosphere, the number of transverse Pc1 (incident EMIC) waves rapidly decreases outside the PP, while their occurrence peak is located considerably equatorward (|ΔMlat| = -5o – -15o) of the PP. On the other hand, the compressional Pc1 waves can propagate in the ionosphere outside the PP towards the poles, while in the equatorial direction there is a secondary maximum in their spatial distribution at low magnetic latitudes. Our results suggest that mode conversion taking place at the plasmapause plays a crucial role in the formation of the presented spatial distributions.