Excitation of the middle latitude ionospheric Alfvén resonator (IAR) due to global thunderstorm activity is considered. The lightning discharges in thunderstorm centers are modeled in terms of a stochastic Poisson process. The lightning onset time and the current moment amplitude are supposed to be random values, while the shape of current moment is assumed to be a given function. Electromagnetic TM mode radiated from the lightning discharges penetrates into the ionosphere via mode coupling to the shear Alfvén and magnetosonic wave modes in the E layer of the ionosphere. The ionospheric resonance cavity can trap and accumulate the shear Alfvén wave energy with periods from one second to a few tenths of seconds, thereby exciting the IAR resonances. Using a simplified model of the topside ionosphere, we have analyzed a possibility for the IAR excitation far from the tropical thunderstorm region. The low‐frequency power spectra of the IAR on the ground surface is studied both analytically and numerically. It is shown that the IAR power spectra exhibit spectral resonance structure (SRS) only during the nighttime conditions. Furthermore, it is found that the calculated spectra are one or two orders of magnitude lower than that observed at Karimshino station in Kamchatka region. This fact suggests that the SRS is not simply due to stochastic lightning discharge process but that some generation mechanisms for the IAR excitation at middle latitudes might also be operative.

—Anomalous variations in radon emissions from the soil are sometimes observed before and after strong earthquakes. In this paper, we theoretically analyze the known hypothesis that these variations in radioactive emanations in the surface layer of the atmosphere cause variations in the vertical background current in the atmosphere with subsequent changes in the electron density $${{n}_{e}}$$ in the lower ionosphere. For this purpose, we will first assess the relation between radon emission variations and the vertical atmospheric current flowing into the ionosphere. Then we will solve a model problem concerning the spatial distribution of plasma density and electric field perturbations occurring in the E -layer of the ionosphere caused by an inflowing vertical current. It was believed that the current flowing into this layer contains only an electron component and is attenuated only by the recombination of electrons. The estimate of the maximum variation $${{n}_{e}}$$ is at least 3–5 orders of magnitude smaller than the observed anomalous variations, which allows us to conclude that this hypothesis is not plausible.

The generation mechanism of the geomagnetic field perturbations associated with tsunami wave propagation in ocean is examined. The geomagnetic perturbations are produced by electric currents generated in both the seawater and conductive layers of the ionosphere. The electric current in conductive seawater is caused by the seawater motion due to tsunami wave propagation whereas the current in the ionospheric plasma is generated by acoustic gravity wave (AGW) incident on the ionosphere from the atmosphere. The AGW is originated from vertical displacements of seawater surface due to the tsunami wave propagation. Although the ionospheric plasma conductivity is much lower than the seawater conductivity, the electric current in the ionosphere can be greater than that in the seawater due to an exponential increase of amplitude of the upward-propagating AGW. Our calculations are indicative of the possibility of space monitoring of tsunami wave based on onboard measurements of the geomagnetic field perturbations.

Approaches to magnetotelluric monitoring of variations in apparent resistivity and electromagnetic emission that may serve as earthquake precursors are considered. Monitoring of apparent resistivity is advised in the range 7–300 Hz, where natural electromagnetic fields exhibit stable behavior, while at lower frequencies the behavior of the electrotelluric and magnetic fields should be analyzed. We present results of studies aimed at identifying active faults and searching for stress–strain sensitive zones for installing measurement equipment based on the registration of tidal variations in apparent resistivity. The features of apparent resistivity anomalies preceding earthquakes in China based on direct current measurements are discussed. Based on the analysis of natural electromagnetic field monitoring in the ULF and ELF ranges in China, the anomalies recorded prior to several recent earthquakes are considered. Before the Yangbi earthquake (2017) and the series of Yangbi (2021) and Ninglang (2022) earthquakes, variations in apparent resistivity were observed that have a pulsed behavior and probably are manifestations of electromagnetic emission. Possible sources of these anomalies are active faults located near the monitoring stations.