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.

The electromagnetic and electrostatic fields from powerful lightning heat and ionize the lower ionosphere. The disturbances appear as halos, sprites and elves, and are also observed as perturbations in crossing radio signals. The characteristic of the lightning discharges leading to the various types of perturbations is not fully understood. Here we present an analysis of 63 elves and corresponding VLF and MF signal perturbations from an almost stationary thunderstorm that allows us to untangle some of the dependencies of perturbations on the lightning characteristics. We characterize the perturbations to a VLF-transmitter signal as “long-recovery-early-events” (LOREs), “early” events, or “rapid-onset-rapid-decay” (RORD) events. We find that LOREs are related to high lightning current and bright elves, and their amplitude and sign depend on their location along the signal path. With observations in the ELF and MF band, we find that lightning with elves has three times the impulse charge moment change (iCMC) and ten times the power than lightning of similar peak current without elves. Attenuation in MF links appear in a higher proportion and longer duration observed with elves than with high peak current lightning without elves. The remaining types of VLF perturbations occur without TLEs but with sequences of lightning that produce slowly rising CMCs reaching high values (up to ~3500 C km within ~500 ms). Slower rise times lead to lower fields in the mesosphere that may not create significant ionization but instead drive dissociative attachment of free electrons. The depletions can result in perturbations to crossing VLF signals.

We present a multi-instrumental analysis of a 20-hour duration Mesoscale Convective System (MCS) over the northwestern Mediterranean sea on September 21, 2019, that produced 21 sprites recorded with a video camera, of which 19 (90$\%$) were dancing sprites. The asymmetric trailing stratiform MCS developed in strong convective conditions (3500 J kg$^{-1}$) and formed a large and persistent overshoot with several convective cores (up to 25,000 km$^2$ with cloud top temperature $<$ -66$^{\circ}$C). It exhibited a bow echo structure with a probable inverted charge dipole within the convective region before the main sprite production period and associated with a large decrease of the negative cloud-to-ground (CG) flash rate. The sprite producing positive cloud-to-ground (SP+CG) flashes mainly initiated at the edge of the convective line on the side of the stratiform region. The flashes propagated over long distances (up to $\sim$ 200 km) across it producing both positive and negative CG strokes. Some parent flashes initiated within the stratiform region close to convective structures and propagated reversely. The 19 dancing sprite events included 49 sequences, of which 46 (94$\%$) were associated with distinct SP+CG strokes and 3 with surges during the continuing current. An especially bright and wide sprite sequence was produced by three distinct SP+CG strokes that occurred within 3 ms and separated by 54 km. This sprite sequence could be classified as a new sprite category resembling to a â\euroœwallâ\euro? but structured in three groups, each associated with one of the +CG strokes, but not separated by the video imagery.