ELF Electromagnetic Waves and Ionospheric Physics SeminarNovember 25, 2026Gabriella Sátori (HUN-REN Institute of Earth Physics and Space Science, Sopron, Hungary) "Latitude-Dependent Solar-Cycle Modulation of Global Lightning Area" Abstract: A long-term record of Schumann resonance (SR) frequencies, derived from measurements of the vertical electric field component at Nagycenk (NCK; 47.6°N, 16.7°E), Hungary, covering the period from May 1993 to December 2025, was used to investigate solar-cycle variations in the spatial extent of global lightning activity over three consecutive solar cycles. SR frequencies exhibit diurnal excursions of several tenths of a hertz as the dominant lightning source regions move toward or away from the observation site or pass across nodal regions (Sátori et al., 2024). The magnitude of these daily frequency excursions, referred to as the daily frequency range (DFR), depends on the spatial extent of the regions in which lightning discharges occur randomly. Both model calculations and observations indicate that larger lightning source regions are associated with narrower DFRs, and vice versa (e.g., Nickolaenko and Hayakawa, 2002; Sátori et al., 2024). The mean daily spatial extent of lightning source regions can be estimated from DFR values using calibration curves specific to the NCK station. The lightning area (LA) is systematically larger during Northern Hemisphere (NH) summer than during Southern Hemisphere (SH) summer, reflecting the asymmetry in land distribution between the two hemispheres. Monthly mean LA time series derived from DFR measurements at NCK cover three solar cycles and reveal a clear solar-cycle modulation. During NH summer, the mean LA is larger in solar maximum years (~2002, ~2014, and ~2024) than in solar minimum years (~1996, ~2008, and ~2019), when lightning activity extends to latitudes as high as ~70°N. In contrast, during all other seasons, the mean LA is smaller during solar maximum years and larger during solar minimum years, when lightning source regions are confined to the latitudinal band between ~50°S and ~50°N. This latitudinal distinction can be identified because the annual and semiannual cycles in LA exhibit different sensitivities to the geographic distribution of lightning activity, particularly in latitude. These cycles effectively act as natural spatial filters, making it possible to extract the latitude dependence of solar-cycle modulation from a single, globally integrated Schumann resonance signal Contact: Contact_ELFseminar(at)oa.uj.edu.pl |