Seasonal and Interannual Variations in the Schumann Resonance Observed in the ELF Electromagnetic Networks in China.

Based on 9 years of quasi‐continuous data observed at extremely low‐frequency electromagnetic stations, the long‐term variations of Schumann resonances (SRs) are compared and analyzed. We obtained two major parameters, namely the peak intensity and peak frequencies by Lorentz fitting and focus on their seasonal and interannual variations of the first three modes in 10 stations. Fengning station was taken as an example to show the seasonal variations of the intensity and frequency of each electromagnetic component and each mode of SR, with the intensity reaching the maximum in Northern Hemisphere summer and minimum in winter; while the frequency has an inverse phase. And the amount they change from summer to winter also shows different characteristics. The interannual variation of the 10 stations shows the unified law of change in the magnetic field than in the electric field. Finally, in conjunction with observations from other regions of the globe, the periodic intensity variation and migration of the lighting activities were considered the dominant controlling factors for the SR parameters. And by comparing with the El Niño index and solar X‐radiation flux, the strong links between SR parameters and the 11‐year solar cycle are confirmed, and intensity enhanced under the influence the 2015/2016 super E1 Niño phenomenon. Plain Language Summary: Schumann resonance (SR) is an electromagnetic phenomenon displayed in the low‐frequency band. The Earth's surface and the bottom boundary ionosphere form a cavity that enables specific frequency enhancements. Three major sources of lightning on Earth act as the sources, and due to the extreme low attenuation of electromagnetic waves, their radiated signals can be observed anywhere on Earth. We use ground‐based observations of the natural electromagnetic field to obtain SR information. By analyzing the seasonal and interannual variation of the intensity and frequency in the first three SR modes, we have a preliminary understanding of the SR periodic variation characteristics. We subsequently aim to explain the main reasons for these variations. The intensity changes and the migrations of thunderstorm activity play important roles in the seasonal SR variation. The interannual variation of the frequency and intensity is synchronous with the solar activity, and there is an 11‐year period, while the long‐term variation pattern of the intensity is controlled by global temperature change, especially the super El Niño phenomenon. Key Points: Long‐periodic variation in the Schumann resonance (SR) parameters is examined at 10 extremely low‐frequency electromagnetic stations in ChinaCorrelations are confirmed among the SR parameters, global climate change, and the solar activity cycle [ABSTRACT FROM AUTHOR]