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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. Lightning is recognized as a climate variable indicating the changing climate of the Earth. Surface temperature changes on the order of 1°C can result in a significant change in lightning frequency. Lightning activity is monitored on a global scale by satellites and by ground‐based global lightning detection networks. However, the detection efficiency of these available technologies is limited which restricts the investigation of global lightning activity especially on the day‐to‐day time scale. In this study, we propose an alternative method to monitor day‐to‐day changes in global lightning activity based on Schumann resonance measurements and thus we compare SR‐based observations with available global lightning monitoring techniques. We show that the overall intensity of global lightning activity can vary considerably (by a factor of 2–3) within a few days, further motivating our efforts to monitor such changes and understand their causes. It is also clear from our study that new methods are needed to quantitatively characterize continental‐scale lightning activity. Daily average Schumann resonance intensity is a quasi‐global invariant quantity that shows good agreement with global daily stroke rates and thunder hoursGlobal lightning activity can vary by a factor of 2–3 on a 3–5 day timescale which could be attributed to cold air outbreaksCurrently available technology does not allow the detailed quantitative evaluation of lightning activity on continental scales Daily average Schumann resonance intensity is a quasi‐global invariant quantity that shows good agreement with global daily stroke rates and thunder hours Global lightning activity can vary by a factor of 2–3 on a 3–5 day timescale which could be attributed to cold air outbreaks Currently available technology does not allow the detailed quantitative evaluation of lightning activity on continental scales

Results of ionospheric disturbances observations using multisite total electron content (TEC) measurements over the Antarctic Peninsula for the period from 2009 to 2012 are presented. Diurnal dependencies of the disturbance occurrence frequency, velocity, and direction of motion are established. Parameters of the disturbances are calculated using dynamic approach to the problem of ionospheric disturbances diagnostics which has been extended to allow for an arbitrary waveform of TEC perturbations. Specific data quality constraints are introduced to determine the presence of wavelike disturbances in the TEC records and to satisfy the required accuracy of parameter reconstruction. Statistical treatment of the results shows that during the daytime disturbances propagate predominantly in the northern and northeastern directions. In the evening and nocturnal hours the northwestern direction is prevailing, with the characteristic disturbance velocities ranging from 10 to 250 m/s. The most probable velocities are tens of meters per second, while the mean values are equal to about 100–130 m/s. In the daytime the velocities of the ionospheric disturbances are even higher. During the Antarctic winter time disturbances are usually observed at local noon time, in sharp contrast with the summer time, when they are present during the nights and mornings. Evidence for neutral wind filtering effect in the lower ionosphere is shownTIDs propagation direction depends on geomagnetic conditionsTID parameters can be derived from GNSS TEC data

A statistical picture of the occurrence and characteristics of Traveling Ionospheric Disturbances (TIDs) over the Antarctic Peninsula is established using Global Navigation Satellite System Total Electron Content and High Frequency sounding observations. The measured parameters of the majority of the disturbances allow classifying them as medium scale TIDs (MSTIDs). Overall, the observed climatology of ionospheric disturbances in the Antarctic Peninsula region varies significantly with the season and makes it possible to differentiate two major types of the disturbances: winter daytime and summer nighttime, based on their occurrence periods and characteristics. During the Antarctic summer period, the disturbances are present mainly during the nighttime and morning hours, when the background plasma density is at maximum (due to Weddell Sea Anomaly). These disturbances predominantly propagate northwestward and their occurrence probability is well correlated with the sporadic E layer observations, suggesting that these are electrified MSTIDs. During the winter, the TID events are almost exclusively observed during the daytime. The propagation direction of the disturbances during the daytime shows a strong correlation with the background neutral wind direction in the thermosphere. A possible mechanism for this effect is wind filtering of the Atmospheric Gravity Waves originating in the troposphere, which indicates that their source is in the lower atmosphere. The periods of the TIDs also significantly differ between the seasons. Wintertime TIDs have noticeably shorter periods (10–50 min) than those observed during other parts of the year (30–140 min), which also likely reflects the fact that the two types of TIDs are generated by different physical mechanisms. Majority of Traveling Ionospheric Disturbances (TIDs) observed in Antarctica are medium scale TIDsTwo major peaks in TID occurrence is observed: winter daytime and summer nighttimePropagation direction of daytime TIDs is primarily controlled by neutral wind Majority of Traveling Ionospheric Disturbances (TIDs) observed in Antarctica are medium scale TIDs Two major peaks in TID occurrence is observed: winter daytime and summer nighttime Propagation direction of daytime TIDs is primarily controlled by neutral wind

A study is presented of artificial ionospheric turbulence (AIT) induced by HF heating at High Frequency Active Auroral Research Program (HAARP) using frequencies close to the fourth electron gyroharmonic, in a broad range of radiated powers and using a number of different diagnostics. The diagnostics include GPS scintillations, ground‐based stimulated electromagnetic emission (SEE), the HAARP ionosonde, Kodiak radar, and signals received at the Ukrainian Antarctic Station (UAS). The latter allowed analysis of waves scattered by the AIT into the ionospheric waveguide along Earth's terminator, 15.6 mm from the HAARP facility. For the first time, the amplitudes of two prominent SEE features, the downshifted maximum and broad upshifted maximum, were observed to saturate at ~50% of the maximum HAARP effective radiated power. Nonlinear effects in slant total electron content, SEE, and signals received at UAS at different transmitted frequencies and intensities of the pump wave were observed. The correlations between the data from different detectors demonstrate that the scattered waves reach UAS by the waveguide along the Earth's terminator, and that they were injected into the waveguide by scattering off of artificial striations produced by AIT above HAARP, rather than via direct injection from sidelobe radiation. Several independent diagnostic techniques were used to study AIT induced by HAARP near the fourth gyroharmonicHF waves from HAARP were scattered by the AIT into the ionospheric waveguide and detected at the UAS 15.6 mm away

This paper describes a system for multi‐position Doppler ionosphere sounding implemented at the beginning of 2018 in the Kharkiv region of Ukraine, the data processing technique and initial results of data analysis. The system comprises a high frequency (HF) transmitter and three receiving sites making almost a right triangle with catheti of 32.8 and 58 km. The transmitter continuously emitting a monochromatic signal of a ∼20 W power at a frequency in most cases slightly lower than foF2is located in the city of Kharkiv. The foF2value was permanently controlled by the ionosonde installed in about 45 km from the transmitter. We report and discuss the initial results of traveling ionospheric disturbances (TIDs) observations for three years since January 2018 until December 2020. Statistical distributions of the frequency of appearance, periods, horizontal speeds, and propagation directions of TIDs are presented. The range of their most probable wavelengths is from 120 to 260 km, while their propagation velocities are from 80 to 220 m/s. The preferred direction of the TID propagation changes during the daytime and shows a tendency to rotate clockwise in azimuth. Notably, such regular long‐term measurements in the Eastern Europe have been carried out for the first time. We describe a novel multi‐position high frequency Doppler facility in Ukraine and data processing technique capable of exploring the traveling ionospheric disturbances (TID) parametersVariations of the Doppler frequency shift from each of three sites revealed the salient TID characteristics in several case studiesStatistical distributions of the appearance frequency, periods, horizontal speeds, and directions of TIDs during a few years are presented We describe a novel multi‐position high frequency Doppler facility in Ukraine and data processing technique capable of exploring the traveling ionospheric disturbances (TID) parameters Variations of the Doppler frequency shift from each of three sites revealed the salient TID characteristics in several case studies Statistical distributions of the appearance frequency, periods, horizontal speeds, and directions of TIDs during a few years are presented

Observations of traveling ionospheric disturbances (TIDs) associated with atmospheric gravity waves (AGWs) generated by the moving solar terminator have been made with the Millstone Hill incoherent scatter radar. Three experiments near 1995 fall equinox measured the AGW/TID velocity and direction of motion. Spectral and cross-correlation analysis of the ionospheric density observations indicates that ST-generated AGWs/TIDs were observed during each experiment, with the more-pronounced effect occurring at sunrise. The strongest oscillations in the ionospheric parameters have periods of 1.5 to 2 hours. The group and phase velocities have been determined and show that the disturbances propagate in the horizontal plane perpendicular to the terminator with the group velocity of 300–400 m s-1 that corresponds to the ST speed at ionospheric heights. The high horizontal group velocity seems to contradict the accepted theory of AGW/TID propagation and indicates a need for additional investigation.