Volodymyr Grimalsky

Ionospheric space weather (ISW) is formed when LEAIM system is impacted by powerful sources located above the ionosphere (from solar wind and magnetosphere during strong magnetic storms), within atmosphere-ionosphere (lightnings; instabilities in active nonlinear atmosphere-ionosphere), and below the ionosphere (in the lower atmosphere or within Earth, including hurricanes, earthquakes, and volcanoes). One of the key issues in understanding mechanisms of ISW formation is the study, modeling, and comparison with experiment of processes of interactions and propagation of wave disturbances in "vertical" and "horizontal" (latitude-longitude) directions in open dynamic active/dissipative LEAIM system, including the ionosphere. Synergistic approach required for such studies requires multiparameter ground-based and satellite methods for diagnosing ionospheric plasma structures (IPS), including Traveling Ionospheric Disturbances (TIDs). Radio diagnostics, including the use of GNSS data, LOFAR (Low-FRequency Radio Telescope Array), Ionosondes, VLF (Very Low Frequency/kHz) Radio Waves in the Earth-Ionospheric Waveguide, etc., constitutes an important part of radio diagnostic methods. In particular, methods and models for excitation of electromagnetic waves (EMW) and acoustic-gravity waves (AGW) by current and hydrodynamic/thermal sources are being developed and will be presented, including lightning sources EMWs in lower atmosphere and mesosphere associated with volcanoes; excitation of AGW and EMW by ground and lithospheric current sources associated with seismic processes; excitation by ionospheric current-thermal sources of AGW/IPS/TIDs (Travelling Ionospheric Disturbances), penetrating from upper to middle and low latitudes; these sources are located at high latitudes/auroral oval or middle latitudes, and they are associated with the penetration of magnetospheric currents into ionosphere during magnetic storms; solar terminator as a source of AGW/TIDs; developing Perkins instability in the middle-latitude ionosphere in the presence of AGWs as a seeding factor and radio wave scattering on the excited nonlinear IPS; models of scattering of high-frequency EMW/LOFAR (MHz) radio waves on IPS. The following breakthrough experimental-theoretical results in the field of atmospheric electricity theory will be presented. (1) Hunga Tonga volcano eradication (HTVE) (January 2022) caused unprecedented lightning currents in lower atmosphere of order 5*10-7 A/m2, exceeding fine-weather current by 5 orders of magnitude; unprecedented influence of radon on conductivity, electric and magnetic fields in the lower atmosphere in region of Popocatepetl volcano was discovered; electric field can exceed the fine-weather field by 5 orders of magnitude, with coronal discharge between charged cloud and volcano cone. Therefore seismogenic electromagnetic fields of ULF and ELF (Ultra- and Extremally Low frequencies, respectively) and VLF ranges penetrate into ionosphere and are capable to form ISW; (2) new model of planetary-scale MHD/AGW vortex structures gives spatial periods and velocities which are in agreement with ionospheric satellite observations; (3) combined complex-geometrical optics-beam method for radio weave scattering on the IPS/TIDs is developed; birefringence and dependence of radio wave frequency on the TID velocity is included; astrophysical sources are used as “projectors” irradiating the IPS under investigation, while LOFAR is used as a detector of the scattering waves; (4) new model of AGW/TIDs excitation by solar terminator provides characteristics parameters (periods, velocities) and tiny peculiarities of structures corresponding to GNSS and LOFAR observations.

This work presents the analysis of a normally open, electrothermally actuated double-layer microgripper using a chevron device. A Silicon-On-Insulator (SOI) wafer is used for its implementation, consequently the structural layer is made of silicon, in this case, with a thickness of 70 μm, The materials used to implement the upper layers of the double-layer microgrippers are silicon nitride (Si3N4) and polysilicon (Poly-Si), with three different thicknesses: 1, 2 and 5 μm, The highest values of displacement and reaction force, determined at the tips, considering both single- and double-layer microgrippers, correspond to the double-layer gripper, designed with the upper layer of polysilicon of 5 μm.

Over the past 10 years, increasingly intensive studies of ionospheric plasma structures have been carried out using data from the Low-Frequency Array for radio astronomy (LOFAR) radio telescope system. Recently more and more attempts are taken to combine LOFAR ionospheric studies with other monitoring techniques such as GNSS observations. LOFAR detects scattering of high-frequency (HF) (MHz) electromagnetic waves (EMW) on the above-mentioned plasma structures. Astrophysical sources of such EMWs may be, for example, radio galaxies, supernovae remnants and pulsars. The plasma structures under investigations are excited due to impacts on the ionosphere “from below”, namely powerful natural hazards, including typhoons, volcanoes and earthquakes, and “from above”, in particular strong magnetic storms, accompanied by corresponding disturbances of auroral currents and due to flows of charged particles; as well as because of solar flares, eclipses and the terminator, as well as various plasma instabilities and nonlinearities, etc. Now we are focusing on identifying quasi-periodic and quasi-wave ionospheric disturbances in the low frequency range, including traveling ionospheric disturbances (TIDs). Results will be presented (1) based on developed models of linear and nonlinear TIDs in the presence of corresponding linear and nonlinear atmospheric gravity waves (AGWs); (2) appropriate modulation of the ionospheric plasma; (3) examples of scattering of high-frequency (HF) (MHz) electromagnetic waves (EMWs) on plasma structures, including the characteristics of the Doppler shift on moving plasma structures, taking into account birefringence in ionospheric plasma, as well as results regarding the qualitative influence on the scattering characteristics of EMWs such factors as height and horizontal dimensions of the ionospheric plasma scatterer. Algorithms are being developed to take into account the influence of plasma resonances and photochemical interactions on the characteristics of emerging ultra-low frequency (ULF) plasma structures. A database has been created that includes dynamic spectra of plasma disturbances with reference to the times of sunrise and sunset over a number of months in 2024. Observations of plasma structures were carried out at various LOFAR stations. Slant TEC maps are being developed on the basis of GNSS data. Spectral processing (using in particular Fast Fourier Transform, wavelets and transformation from dynamic spectra to Doppler shifter spectra) of the LOFAR and GNSS data is carried out with the aim of identifying quasi-periodic and quasi-wave ultra-low frequency (ULF) plasma structures with subsequent comparison “Theory-Experiment”.

The 2022 Hunga Tonga Volcano Eruption (HTVE) had unprecedented impacts on atmospheric space weather. It provided a clear example of how space weather may be impacted by influences both “from above” (e.g. the solar wind, geo-magnetic storms) and “from below” (e.g. powerful volcanoes, hurricanes, earthquakes). Manifestations of unprecedented geophysical effects from HTVE were an acoustic wave that circled the Earth several times, the formation of strong ionospheric plasma bubbles and plasma depletion. An important method for diagnosing ionospheric space weather is ionospheric radio scintillation (IS). The purpose of this work is data analysis, modelling and interpretation of radio scintillation data of ionospheric effects from HTVE using the Low-Frequency Array (LOFAR), supported by observations from the European Space Agency’s Swarm mission and other geophysical instruments. Specifically, LOFAR observed TIDs in the ionospheric plasma over the Europe, which, based on typical velocities and pulse widths (on the order of 10 s), are interpreted as the effect of waves generated as a result of the HTVE. The physical modelling carried out corresponds to a picture corresponding to the penetration of Lamb waves into ionospheric altitudes, with their source being a pressure pulse associated with HTVE. Moreover, the corresponding physical explanation, based on the modelling carried out, is given from two points of view: (1) acoustic mode and (2) acoustic impulse representations. (1) Modes with periods of about 12 min were studied. It turned out that such frequencies correspond to a number of eigenmodes of Lamb waves which, accounting for attenuation, travelled thousands of km from the source to the observation site and having a finite/non-zero excitation efficiency (velocity value) near the Earth’s surface. At the same time, the acoustic field of such waves is concentrated at the heights of the altitude region of the E region of the ionosphere. (2) It has been shown that a pressure pulse with a duration of about 10 s in the lower atmosphere effectively penetrates to the heights of the E region of the ionosphere, its acoustic field is concentrated in the E region and it tends to propagate in the horizontal direction, exciting the E region. An analytical algorithm is proposed to determine the response of the ionosphere to the corresponding acoustic pulse, and a method of complex geometric optics is presented, which makes it possible to simulate the scattering of high-frequency (HF) electromagnetic waves (EMW) in the LOFAR (MHz) range. In general, the observations, estimates and numerical simulations confirm the effect of pulsed impact on the ionosphere of acoustic waves penetrating to ionospheric heights at distances of many thousands of kilometres from the source associated with HTVE and causing the scattering of HF EMW detected by the LOFAR radio telescope. The above-mentioned model is under development now. Its appropriate application will allow us to study and interpret other effects of acoustic waves from a source associated with HTVE and develop further the methods for radio diagnostics of ionospheric space weather.

Radio diagnostics, including scattering of electromagnetic waves (EMW) by spatiotemporal disturbances of the ionospheric plasma in the ELF (Extremely Low Frequencies, Hz), VLF (Very Low Frequencies, kHz), HF (High Frequencies, MHz) and microwaves (GHz) ranges, is one of the most effective methods for detecting and studying extreme modifications of ionospheric “space weather”. Such modifications are caused, in particular, by influences “from above” (from the Solar wind and magnetospheric storms) and “from below” (from tropical cyclones, earthquakes and volcanoes) and other Natural Hazards. Such ionospheric modifications are manifested, in particular, in the excitation of TIDs (Traveling Ionospheric Disturbances) and scintillations on various scales of the HF waves detected by LOFAR (Low Frequency Array) Radio Telescope.In combination with other ionosphere sounding techniques (as GNSS) LOFAR can give a complementary insight to the ionospheric structures. We present LOFAR scintillation observations compared with GNSS-observed ionospheric irregularities in order to assess the ionospheric plasma structures. Classified ionospheric scintillation data will be presented. These include quasi-periodic, quasi-pulse, flare-like and other disturbances detected on the LOFAR radio telescopic systems in Poland, Great Britain, Germany and other countries. Spectral processing of LOFAR data is currently being carried out to identify various types of ionospheric disturbances, including TIDs, that characterize ionospheric space weather. We are currently developing TID modelling methods aimed at comparison with experimental data. Theoretical and experimental data on ionospheric disturbances associated with the eruption of the Hunga-Tonga-Hunga-Ha'apai volcano in January 2022 are presented and the results of their comparison are discussed. Based on the data-driven approach, effective current sources associated with lightning discharges caused by the eruption of the Hunga-Tonga-Hunga-Ha'apai volcano are identified in the ULF (Ultra-Low Frequency), ELF and VLF ranges. In particular, theoretical results are given on: (i) the excitation of the first and second modes of the Schumann resonator; (ii) the fundamental possibility of simultaneous excitation of coupled global Schumann and local Alfvén resonators. The results of applying the model for the scattering of HF electromagnetic waves (EMWs) on ionospheric disturbances such as increased and decreased plasma densities will be presented. The effects of birefringence, the dependence of EMW frequency on time in moving plasma, diffraction and dispersion of EMWs will be included, based on the advanced method of Complex Geometrical Optics.An information is provided on the Ukrainian Ground-Based Space Weather Monitoring Network. This network includes GNSS stations, VLF receivers, Magnetotelluric stations, Ionosonde and magnetometer INTERMAGNET. Examples of corresponding measurements are presented.Yu.R. and L.B. are grateful, for partial funding this research, by National Science Centre, Poland, grant No 2023/49/B/ST10/03465, “Modern Radio-Diagnostics of the Ionosphere using LOFAR and GNSS Data”

The simulations presented here are based on the observational data of lightning electric currents associated with the eruption of the Hunga Tonga volcano in January 2022. The response of the lithosphere (Earth)–atmosphere–ionosphere–magnetosphere system to unprecedented lightning currents is theoretically investigated at low frequencies, including ultra low frequency (ULF), extremely low frequency (ELF), and very low frequency (VLF) ranges. The electric current source due to lightning near the location of the Hunga Tonga volcano eruption has a wide-band frequency spectrum determined in this paper based on a data-driven approach. The spectrum is monotonous in the VLF range but has many significant details at the lower frequencies (ULF, ELF). The decreasing amplitude tendency is maintained at frequencies exceeding 0.1 Hz. The density of effective lightning current in the ULF range reaches the value of the order of 10⁻⁷ A/m². A combined dynamic/quasi-stationary method has been developed to simulate ULF penetration through the lithosphere (Earth)–atmosphere–ionosphere–magnetosphere system. This method is suitable for the ULF range down to 10⁻⁴ Hz. The electromagnetic field is determined from the dynamics in the ionosphere and from a quasi-stationary approach in the atmosphere, considering not only the electric component but also the magnetic one. An analytical/numerical method has been developed to investigate the excitation of the global Schumann resonator and the eigenmodes of the coupled Schumann and ionospheric Alfvén resonators in the ELF range and the eigenmodes of the Earth–ionosphere waveguide in the VLF range. A complex dispersion equation for the corresponding disturbances is derived. It is shown that oscillations at the first resonance frequency in the Schumann resonator can simultaneously cause noticeable excitation of the local ionospheric Alfvén resonator, whose parameters depend on the angle between the geomagnetic field and the vertical direction. VLF propagation is possible over distances of 3000–10,000 km in the waveguide Earth–ionosphere. The results of simulations are compared with the published experimental data.

The nonlinear conductivity of 2D electron gas in graphene and 3D electron gas in the narrow-gap n-InSb semiconductor has been simulated in terahertz (THz) range by various methods including the direct quantum approach, the quasi-classical kinetics, and the quasi-relativistic hydrodynamics. These methods yield the same results under the electron temperatures ≤100 K when the kinetic electron effective mass used in the nonlinear hydrodynamics is equal to the effective mass in n-InSb and it is equal to some nonzero mass that depends on 2D electron concentration in the graphene. The linear resonant dependencies of the complex electron conductivity are simulated both from the kinetic theory and from the hydrodynamic one. The kinetic dependencies of the resonant conductivity on frequency coincide with ones obtained from the hydrodynamic theory under realistic electron concentrations and collision frequencies. Thus, the nonlinear hydrodynamic equations are valid to describe the nonlinear dynamics of the electron gas in graphene and in n-InSb. The nonlinear hydrodynamics has been applied for simulations of nonlinear propagation of THz electromagnetic waves through the multilayer structures dielectric - graphene or n-InSb - dielectric placed in a bias magnetic field. The simplest three-layer structures demonstrate the sharp nonlinear switching of the transparency of THz waves and the bistability under relatively low values of amplitudes of the incident electromagnetic wave.

The noise-like behavior of geomagnetic anomalies observed in Tlamacas station (the Popocatepetl volcano, Mexico), linked to the ionization produced by intensive radon release, is presented in the experimental part of the study. The magnetic-field perturbations produced by electrical currents due to micro-discharges on the terrain irregularities are considered in a theoretical model. The simulations demonstrated that the discharge mechanism can generate perturbations with magnitudes of up to 1–10 nT in the ultra-low frequency (ULF)) range of 10⁻³–10⁻¹ Hz. ULF Magnetic-field perturbations can be higher within storm-weather conditions under an accumulation of electric charges in clouds in the mountainous regions.

We have used 2014–2017 data from the eight receiving stations of the Japan very low frequency (VLF) monitoring network. The nighttime data of the signals of the JJI transmitter on Kyushu Island, excited VLF electromagnetic waves (EMWs) in the Earth-Ionosphere waveguide (EIWG) had been processed. The wavelet transform with a preliminary detrending, to exclude influence of daily variations, has been applied. We have observed ultra-low frequency (ULF) modulation of VLF EMW spectra in the EIWG. We therefore concluded that modulating oscillations with periods of 4 minutes belong to the acoustic branch of acoustic-gravity waves (AGWs) in the Earth–Thermosphere waveguide; modulation of VLF with periods of 6–7 minutes corresponds to global evanescent/reactive Brunt–Väisälä AGW oscillations; the oscillations with periods 20–60 min and ~3 hours may characterize evanescent/reactive Lamb gravity wave mode of AGW [1]. The appearance of the combination frequency of VLF EMW and ULF AGW is likely due to the following effects: (1) the drag of charged plasma particles by ULF AGWs jointly with the background of VLF electron density disturbances and (2) the motion of charged plasma particles in the VLF EMW field jointly with the background of ULF changes in the plasma concentration caused by AGWs.The theory [2,3] is extended to the excitation of ionospheric Schumann resonator (SR) [4] and ionospheric Alfvén resonator (IAR) in the ULF range. It is shown that IAR oscillations with a high quality factor (for geophysical resonators) (>10) can be excited in the SR range. The features of the excited ULF and VLF modes associated with the modification of the ionosphere as a result of the powerful eruption of the Hunga-Tonga volcano are under consideration [5,6].A ULF model of perturbations in the atmosphere-ionosphere with a boundary transition from dynamic to static limit is developed and the preliminary results of the corresponding modelling will be presented. This ensures the "recovery" of magnetostatic disturbances "lost" in most of previous models of the atmospheric electrical circuit, important for understanding the mechanisms of seismo-ionospheric coupling, volcano-ionospheric coupling and influences of the other natural hazards on the ionosphere and ionospheric monitoring of the natural hazards.[1] Rapoport et al. Sensors 22, 10.3390/s22218191, 2022; [2] Grimalsky et al. JEMAA 2012, 4, 192-198 ; [3] Yutsis V. et al. Atmosphere 2021, 12, 801 ; [4] Nickolaenko and Rabinovich Space Res. 1982, XX, 67-88 ; [5] Astafyeva et al. GRL, 2022 ; [6] D’Arcangelo et al., Rem. Sens., 14, 3649, 2022.This research was partially funded by the National Science Centre, Poland, grant No. 970 2022/01/3/ST10/00072