Diurnal variation in the effect of the weekend in global seismic activity

The influence of the earthquake probability diurnal variation on specific features in the weekend effect in global seismic activity is revealed. The dependence of the global earthquake number on the local time and its possible relation to a quiet solar diurnal variation (Sq) in the geomagnetic field have been considered in detail. It has been indicated that a stable diurnal effect, which has a maximum near midnight and a minimum near local noon, exists in the global seismicity of the Earth. The diurnal variation amplitude changes insignificantly during days of week and substantially decreases (by a factor of almost 3) on Saturday and Sunday. The weekend effect is not revealed during “local nights.” Since the daily effect of a quiet solar diurnal variation (Sq) should not depend on days of week, we arrive at the conclusion that the diurnal variation in global seismicity evidently contains the anthropogenic activity product. The Sunday effect in the earthquake number decreases over the course of time and is most probably real but weak and not stationary since weekly variations occur against a background (or under the action) of stronger variations, i.e., an increase in the earthquake number and diurnal variations.     

Ionospheric response to the entry and explosion of the South Ural superbolide

The South Ural meteoroid (February 15, 2013; near the city of Chelyabinsk) is undoubtedly the best documented meteoroid in history. Its passage through the atmosphere has been recorded on videos and photographs, visually by observers, with ground-based infrasound microphones and seismographs, and by satellites in orbit. In this work, the results are presented of an analysis of the transionospheric GPS sounding data collected in the vicinity of the South Ural meteoroid site, which show a weak ionospheric effect. The ionospheric disturbances are found to be asymmetric about the explosion epicenter. The received signals are compared, both in shape and amplitude, with the reported ionospheric effects of ground level explosions with radio diagnostics. It is shown that the confident registration of ionospheric effects as acoustic gravity waves (AGWs) by means of vertical sounding and GPS technologies for ground explosions in the range of 0.26–0.6 kt casts doubt on the existing TNT equivalent estimates (up to 500 kt) for the Chelyabinsk event. The absence of effects in the magnetic field and in the ionosphere far zone at distances of 1500–2000 km from the superbolide explosion epicenter also raises a question about the possibility of an overestimated TNT equivalent. An alternative explanation is to consider the superposition of a cylindrical ballistic wave (due to the hypersonic motion of the meteoroid) with spherical shock waves caused by the multiple time points of fragmentation (multiple explosions) of the superbolide as a resulting source of the AGW impact on ionospheric layers.     

Dynamics of artificial plasma clouds in “SPOLOKH“ experiments : Cloud deformation

Data on the evolution of the density profiles of the neutral and ionized components of barium clouds obtained in “Spolokh” experiments are presented. The ion density in the cigar-like structure exceeds by more than an order of magnitude that of the background plasma, while the density in the plasma tail out flowing from the cigar-like structure is of the same order as that of the background plasma. The Ba⁺ outflow rate is determined. The results agree with observed cloud motion and with the estimates following from Dzubenko et al. (1983).     

Perturbation Features Imprinted on Ionosphere by Successive Clusters of Strong Earthquakes: Role of Atmospheric Coupling Dynamics

Geomagnetism and Aeronomy - The paper presents atmospheric coupling physics through identifying a few significant features imprinted on the ionosphere by certain unique seismic environments when a...     

Dynamics of artificial plasma clouds in “Spolokh” experiments: Movement pattern

The data on space location and movement of the high-density (n_c? n_b) barium clouds injected at midlatitudes during the “Spolokh-1” and “Spolokh-2” shaped-charge experiments in the ionosphere are presented. At the initial stage, the neutral and ionized components move together at a speed of the neutral wind. An outflow of ions in the form of a stratified tail was also observed. Its movement is interpreted as a drift in [E₀ × B] fields. The evolution pattern of artificial plasma clouds agrees with the qualitative scheme described in the paper.     

Controlled injection of high-power radio pulses into the ionosphere-magnetosphere system and appearance of microsubstorms on October 2, 2007

Insignificant geomagnetic disturbances, which originated during the experimental injection of high-power radio pulses into the magnetosphere-ionosphere system with the help of an HF transmitter of the Sura heating facility, are considered. The experiment was performed at 1840–1900 UT on October 2, 2007 (～2100 MLT) at geomagnetic latitudes close to the zone of generation of the current wedge westward branch, responsible for geomagnetic substorms. The series of two magnetic microsubstorms, with a sudden initial pulse and an insignificant delay relative to the facility switching, was observed at 1840–2000 UT. A disturbance was registered at many stations in the Northern Hemisphere as a global event. The equivalent ionospheric current system of an initial pulse was similar to such a system of the westward auroral surge and had an intensity maximum at Karpogory magnetic observatory, which is the closest station to the Sura facility. Under the conditions of a quiet solar wind and low planetary geomagnetic activity, the AE auroral index correlated with the interplanetary medium parameters (the correlation coefficient reached 0.65) at 1710–2000 UT. It has been confirmed that an initial geomagnetic pulse is generated as a result of radiowave injection. The arguments for and against the generation of microsubstorms due to stimulated precipitation of magnetospheric electrons, as well as the assumption that the geoeffective impact of the interplanetary medium is intensified during the injection of high-power radiowaves near the zone where the westward branch of the current wedge of magnetospheric substorms is generated, are considered.     

Auroral activity caused by high-power radioemission from the SURA facility

A series of experimental modifications of the ionosphere in the HF range, performed at the SURA facility base, together with optical measurements onboard the International Space Station (ISS), indicated that such impacts on the ionosphere are effective when the facility operational frequency is higher than the critical plasma frequency (for the main ionospheric F2 layer). The experimental measurements were supported by measurements at ground-based observatories, ISS, and the Demeter and GPS satellites. The analysis results of the entire data set are presented. The ray HF radio tracing for the experiment of October 2, 2007, has been calculated, and it has been indicated that the ionosphere to the north of the facility up to 60°–62° N latitudes was irradiated by the facility beam (the effects of ray redistribution and refocusing) due to refraction on the gradient of the F2 layer critical frequencies. An analysis of the ground-based and satellite measurements (both in the vicinity of a heater and in the magnetically conjugate region) indicates that it is possible to trigger a substorm in experiments with the Sura heating facility.     

Physical mechanism of ionospheric total electron content perturbations over a seismoactive region

A mechanism for the total electron content (TEC) perturbation in the ionosphere during seismic activity strengthening is proposed. The spatial distribution of the TEC perturbation is shown to be determined by the joint effect of the following two factors: the heating of the ionosphere by electric current and the plasma drift in the electric field of this current. The TEC perturbation behavior depends on the relationship between these processes. The current arises in a global electric circuit as the EMF, which is related to the dynamics of charged aerosols injected into the atmosphere, and comes into being in atmospheric surface layers. The developed model allows calculation of the spatial TEC distribution in the ionosphere for a prescribed horizontal distribution of the charged aerosol concentration at the Earth’s surface.     

The anomaly of plasmapause and ionospheric trough positions from DEMETER data

The paper addresses the study of the specific pattern of the subauroral ionosphere marked with the anomalous positions of the plasmapause, the equatorial boundary of the mid-latitude (main) ionospheric trough, and the light-ion trough under quiet solar and geophysical conditions near the magnetospheric shell with the McIlwain parameter L = 3. The anomaly was identified on the base of data of active experiments with the SURA heating facility on October 2, 2007, which were conducted as part of the SURA-International Space Station (SURA-ISS) program in the framework of the DEMETER satellite mission. Joint analysis of the orbital data from DEMETER and ISS, together with the results of the complex ground-based measurements, shows that the revealed effect, which is characteristic of the premidnight sector north of the Moscow-SURA satellite path, is not local. It is observed in a vast territory, extending from the west to the east along the same L-shell, from at least Sweden to Kamchatka. The conclusions suggested by the DEMETER data are supported by analysis of the meridional distributions of the F2-peak plasma frequencies provided by GPS radio probing of the ionosphere. Comparison of these results with the model latitudinal-longitudinal and meridional distributions of the F2-peak plasma density provided by the IRI 2007 and SMI (Russian standard model of the ionosphere) models shows that the model predictions are at odds with the empirical data.     

Effects Stimulated by Radiation of the SURA Facility in the Geophysical Experiments Program at the International Space Station in 2017

The set of experiments in 2017 included the forecasting of geo- and heliophysical conditions in the ionosphere, the choice of heating regimes at a minimum critical frequency of the F2 ionospheric layer, analysis of the ionosphere radio sounding results and measurements of geomagnetic perturbations using ground-based facilities, study of the potential for higher efficiency and probability of artificial effects on the ionosphere, and the establishment of a correlation between geomagnetic field variations and the radio heating facility cyclogram. The experiments were carried out with a combination of new heating conditions (pulse ratio, period of action, two-frequency and continuous heating, variations in radiated power, polarization, shortwave radiation direction, etc.) in the intervals between recurrent magnetic storms. Geomagnetic field pulsations (in accordance with the cyclogram) and substorm effects were stimulated by the SURA facility against a background of quiet geophysical conditions.