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An increase in the flux of energetic particles under thunderstorm clouds is a result of the multiplication and acceleration of particles of secondary cosmic rays in the electric field of the cloud. Study of the particle multiplication mechanisms requires an assessment of the electrical properties of clouds. In this paper, we propose a method for evaluating the electrical structure of a cloud that creates a flux of energetic particles. The developed technique for estimating the distribution of a charge in the cloud is based on the ground-based measurements of the electric field and energetic particle flux. The technique was used to study the clouds that create the descending fluxes of energetic particles observed at the Aragats Research Station. The characteristic charge distribution involves a two-layer structure with a charge density of 0.5–5 nC/m3 in the lower layer and –0.2…–3 nC/m3 in the upper layer. The total charges of the two charge regions are in the range of 1– 20 and –1…–30 C, respectively.

Thunderclouds act as the sources of energetic radiation, the main components of which are gamma particles and electrons. The radiation can be registered by satellite or ground-based detectors. The effect is caused by the bremsstrahlung of electrons accelerated by the cloud electric field. The study of high-energy atmospheric phenomena requires analyzing the data on the distribution of cloud particles and the electrical structure formed by them. In this study, the comparison of the information on meteorological conditions for energetic emission from thunderclouds obtained from satellite observations in the infrared and optical ranges is performed.

The most important factor determining the dynamics and structure of high-altitude discharges is the significant difference in atmospheric pressure along their length. The Sprite device was designed at the Institute of Applied Physics. It makes it possible to produce an extended concentration gradient of a neutral gas and ignite a large-scale electric discharge in it. This work presents the results of laboratory experiments simulating some properties of high-altitude discharges, primarily sprites and gigantic jets. A high-voltage pulse discharge, which is similar to sprites and gigantic jets in structure, is studied using a wide arsenal of laboratory diagnostics, including macroscopic electrophysical measurements, inductive probes for measurement of the spatial current profile, plasma microwave interferometry, and photography with nanosecond exposures. The similarity of laboratory and natural discharges is shown, and the physical problems and possible means of their solution with limited laboratory simulation are indicated.

A regional system of a short-term forecast of hazardous convective phenomena within WRF-ARW is described. It is shown that major maxima of errors in prognostic temperature and vertical velocity correlate with intense convective events, which indicates the need for additional verification procedures. A new method is proposed for forecasting hazardous convective events based on analyzing the simulated spatiotemporal distributions of the radar reflectivity of an event and comparing them with characteristic parameters (the duration, area, and maximum radar reflectivity) of intense convective events. Threshold values of the area and duration of the event are selected using field observations of powerful convective clouds, while the threshold of the maximum radar reflectivity in the vertical column is tailored for regional features. The method is verified against World-Wide Lightning Location Network (WWLLN) data and ground-based field measurements of the quasi-static electric field. It is shown that, for selected thresholds of duration (20 min) and area (50 km2), the optimal threshold of maximum radar reflectivity for Nizhny Novgorod oblast is 55 dBZ, in which case the Pierce skill score and the Heidke skill score take values of 0.61 and 0.62, respectively.

This review contains the most significant results of Russian studies in the field of atmospheric electricity in 20152018. It is part of the Russian National Report on Meteorology and Atmospheric Sciencesto the International Association of Meteorology and Atmospheric Sciences (IAMAS). The report was presented and approved at the XXVII General Assembly of the International Union of Geodesy and Geophysics (IUGG) 1. The review is followed by a list of the main published works on the studies of atmospheric electricity of Russian scientists in 20152018.

In order to separate global and local effects of atmospheric electricity, measurements of the fair-weather electric field were performed in Nizhny Novgorod in 2013-2018. As a result of processing 139 diurnal records from four observation points spaced 6–8 km apart, diurnal variations in the fair-weather atmospheric electric field for different seasons and weekdays (working days and weekends) were studied. The curve of the local diurnal variation is shown to always have two maxima. The evening maximum of the diurnal variation (19:00–20:00 UT) coincides in time with the maximum of the Carnegie curve, which is a characteristic of the global electrical circuit. The highest values of the field amplitude are reached in the winter period. The field-intensity maximum in the first half of the day (09:00–11:00 LT) is characteristic of the urban environment and shows that local effects associated with the presence of aerosol particles in the air significantly contribute to the formation of diurnal variation, especially in summer. According to the 2013–2018 measurements, the seasonal variation in the monthly-average values of the atmospheric electric field is revealed and analyzed compared with the results of measurements of seasonal variation in other regions of the globe. The obtained results allow one to reveal the role of local effects in the formation of diurnal variation in the mid-latitude areas with temperate continental climate and provide a basis for developing a theory which can explain the physical mechanisms of local effects and suggest appropriate parametrization for finding the surface electric field in the weather and climate models.

The description of global electric circuit (GEC) generators in continuous numerical models is analysed and discussed. It is shown that voltage-source generators, sometimes employed in simple lumped-element GEC models, have a consistent generalisation in continuous GEC models: just as current-source generators generalise to source current density distributions, voltage-source generators generalise to distributions of the relative potential on cloud boundaries. The difference between non-ideal and ideal current or voltage sources is investigated for both lumped-element and continuous GEC models. As in modern three-dimensional GEC models the formal generalisation of voltage-source thunderstorms turns out to be difficult to implement, two alternative approaches involving the replacement of voltage-source generators with equivalent current-source generators are developed. One approach is based upon a rough estimation of the source current producing the same contribution to the GEC as the original voltage source; the other approach uses the fact that each voltage-source generator can be shown to be a limiting case of a certain current-source generator with increased conductivity. For the first time voltage-source generators are implemented in a numerical GEC model (using both the direct generalisation and the suggested alternative approaches).

It is known that the global electric circuit (GEC) intensity can be characterised by a single global index, namely the ionospheric potential (IP), made up of contributions from electrified clouds all over the globe. Using the Weather Research and Forecasting model, we have reproduced the atmospheric dynamics for 2008–2018 and simulated the variation of the GEC by parameterising regional contributions to the IP in terms of convection and precipitation. Considering that the El Nino—Southern Oscillation (ENSO) can be quantitatively characterised by sea surface temperatures (SSTs) in the Nino 3.4 region, this allowed us to identify and study in detail the effect of ENSO on regional contributions to the GEC. Our simulations have shown that contributions to the GEC from the land and oceanic parts of the Earth's surface respond oppositely to the ENSO cycle. The oceanic contribution is positively correlated with the Nino 3.4 SST, largely owing to increases in convection over the Pacific Ocean. In contrast to the oceans, the land contribution shows a negative correlation with ENSO due to decreases in convection over the Maritime Continent and South America. The observed correlations are statistically significant and are clearly seen on the decadal timescale; at the same time contributions to the IP for individual years do not always clearly reflect the corresponding Nino 3.4 SST anomalies. During the two El Ninos and two La Ninas that occurred between 2008 and 2018, the oceanic contribution always changed in phase with ENSO, increasing in El Nino years and decreasing in La Nina years; on the other hand, the contribution of land showed a clear variation in antiphase with ENSO only for the 2015/16 El Nino and 2010/11 La Nina, characterised by extremely large SST anomalies, with a small and indefinite effect for the two lesser events. When summing the contributions of land and ocean, two strong effects of opposite signs nearly counterbalance each other and we obtain a much less pronounced effect of ENSO on the total IP. This effect is generally positive since land and ocean provide nearly equal contributions to the GEC during Northern Hemisphere winters and, according to our analysis, the contribution of ocean is slightly more sensitive to ENSO than that of land.

We consider the relations between the mixed layer height and atmospheric electric parameters affected by convective mixing. Vertical turbulent transport of radon, its progeny and electrically charged particles is described under Lagrangian stochastic framework, which is the next step to develop a consistent model for the formation of electrical conditions in the atmospheric boundary layer. Using the data from detailed and complex measurements of vertical profiles of the temperature and turbulence statistics as input, we calculated non-stationary vertical profiles of radon and its daughter products concentrations, atmospheric electric conductivity and intensity of electric field in the convective boundary layer from the morning transition through early afternoon quasi-stationary conditions. These profiles demonstrate substantial variability due to the changing turbulent regime in the evolving boundary layer. We obtained quantitative estimates of the atmospheric electric field variability range essentially related to the sunrise and convection development. It is shown that the local change in the electrical conductivity is the only factor that can change the intensity of electric field at the earth's surface more than twice during the transition from night to day. The established relations between electric and turbulent parameters of the boundary layer indicate that the effect of sunrise is more pronounced in the case when development of convection is accompanied by an increase in aerosol concentration and, hence, a decrease in local conductivity.

In this paper the contribution of turbulence into the electrification of thunderstorms, snowstorms, and dust storms is investigated for the first time. A model of large-scale electric field generation in a weakly conducting medium, containing two types of particles charging by collisions, is used. Thunderstorm and snowstorm electrification are considered in detail in this paper; dust storm electrification is also considered, despite being substantially different from the two other cases, to demonstrate the universality of the proposed method. A comparison of the results with the experimental data for thunderstorms, blizzards, and dust storms is carried out. It is found that the situation is notably different for inductive and noninductive charge separations. For inductive charge separation there is a range of thunderstorm and snowstorm parameters (conductivity and the particle radii being the most important factors) for which the electric field grows exponentially with time. This effect can make the inductive mechanism dominant near the breakdown field in turbulent zones of thunderclouds. For noninductive (or triboelectric) charge separation caused by intense velocity fluctuations, the electric field strength grows only linearly with time. The most substantial effect of turbulence on noninductive charging is expected to occur in snowstorms and dust storms, whereas noninductive turbulent charging has a little impact on the thunderstorm electrification.

A fair-weather electric field has been observed near the Earth's surface for over two centuries. The field is sustained by charge generation in distant disturbed weather regions, through current flow in the global electric circuit. Conventionally, the fair-weather part of the global circuit has disregarded clouds, but extensive layer clouds, important to climate, are widespread globally. Such clouds are not electrically inert, becoming charged at their upper and lower horizontal boundaries from vertical current flow, in a new electrical regime—neither fair nor disturbed weather; hence it is described here as semi-fair weather . Calculations and measurements show the upper cloud boundary charge is usually positive, the cloud interior positive and the lower cloud boundary negative, with the upper charge density larger, but of the same magnitude (∼nC m −2 ) as cloud base. Globally, the total positive charge stored by layer clouds is approximately 10 5 C, which, combined with the positive charge in the atmospheric column above the cloud up to the ionosphere, balances the total negative surface charge of the fair-weather regions. Extensive layer clouds are, therefore, an intrinsic aspect of the global circuit, and the resulting natural charging of their cloud droplets is a fundamental atmospheric feature.

We developed a hybrid optical pump–x-ray probe facility based on the “Kurchatov’s synchrotron radiation source” and terawatt (TW) femtosecond laser. The bright x-ray photon source is based on either synchrotron radiation [up to 6 × 1014 photons/(s mm2 mrad2 0.1% bandwidth)] or laser-plasma generators (up to 108 photons/sr/pulse). The terawatt (TW) femtosecond laser pulse initiated phase transitions and a non-stationary “extreme” state of matter, while the delayed x-ray pulse acts as a probe. The synchronization between synchrotron radiation and laser pulses is achieved at 60.3 MHz using an intelligent field-programmable gate array-based phased locked loop. The timing jitter of the system is less than 30 ps. In laser-plasma sources, the x-ray and laser pulses are automatically synchronized because they are produced by using the same laser source (TW laser system). We have reached an x-ray yield of about 106 photons/sr/pulse with 6-mJ sub-ps laser pulses and using helium as a local gas medium. Under vacuum conditions, the laser energy increase up to 40 mJ leads to the enhancement of the x-ray yield of up to 108 photons/sr/pulse. The developed hybrid facility paves the way for a new class of time-resolved x-ray optical pump–probe experiments in the time interval from femtoseconds to microseconds and the energy spectrum from 3 to 30 keV.

The global electric circuit (GEC) is a unique atmospheric system driven by the global distribution of thunderstorms and electrified shower clouds. The GEC unites electric fields and currents in the entire atmosphere and is characterized by the permanent production and dissipation of huge amounts of electrical energy. In this study, aimed at investigating the links between the GEC and El Niño—Southern Oscillation (ENSO), the GEC variability during 2008–2018 is simulated on the basis of reanalysis meteorological data using the Weather Research and Forecasting model and a parameterization of the ionospheric potential (IP), which is a natural measure of the GEC intensity. Modelling shows that strong El Niño and La Niña events influence the global distribution of electrified clouds over the Earth’s surface, thereby consistently affecting the shape of the diurnal variation of the GEC. Further analysis shows that anomalies in the Niño 3.4 sea surface temperature, which characterize the ENSO phase, and anomalies in the relative IP are positively correlated at 9:00–15:00 UTC and negatively correlated at 18:00–23:00 UTC. This correspondence between ENSO and the GEC is most prominent at 13:00 UTC and 21:00 UTC, and most pronounced anomalies in the relative IP around these hours are precisely associated with strong El Niño and La Niña events. In particular, during strong El Niños the relative IP is larger than usual around 13:00 UTC and smaller than usual around 21:00 UTC, whereas during strong La Niñas it behaves oppositely.

Complex electrical measurements with the use of sodar data show that electric field pulsation analysis is useful for electrodynamics/turbulence monitoring under different conditions. In particular, the number of aeroelectric structures (AES) generated per hour is a convenient measure of the turbulence intensity. During convectively unstable periods, as many as 5–10 AES form per hour. Under stable conditions, AES occasionally form as well, indicating the appearance of occasional mixing events reflected in the electric field perturbations. AES magnitudes under stable conditions are relatively small, except in special cases such as high humidity and fog. The analysis of electric field (EF) spectra gives additional useful information on the parameters of the atmospheric boundary layer and its turbulence. A rather sharp change in the spectrum slope takes place in the vicinity of 0.02 Hz under stable conditions. The characteristic slope of the spectrum and its change are reproduced in a simple model of EF formation.

In this paper, we present the first results of the ionospheric potential (IP) calculations with the chemistry-climate model (CCM) SOCOL (Solar Climate Ozone Links). For the study, we exploit a parameterization of the difference in electric potential between Earth's surface and lower boundary of the ionosphere as a function of thunderstorm and electrified cloud properties. The model shows a good enough agreement with the IP obtained by balloon soundings. The simulated UT variation of IP exhibits a maximum at 20 Universal time (UT) and minimum at about 2 UT which agree with the UT cycle of the lightning activity. The obtained results allow understanding of IP variability pattern at diurnal, seasonal and annual timescales. We also compare our results with the IP simulated with the climate model INMCM4 using similar IP parameterization. The comparison shows a good agreement of UT cycles especially before 12 UT. Simulated IP annual cycle reaches its maximum in late spring in both models. However, the comparison also reveals some differences in amplitudes of IP variability on different time scales. The large deviations occur after 12 UT for all seasons except summer where the maximum of both results happens before 12 UT. The UT cycle of IP simulated with CCM SOCOL is in a better agreement with observations after 12 UT in terms of phase with similar timing of maximum values. The calculation of IP using climate models can help to fill up the gaps when the observed IP is not available. The interactive calculation of IP is also a step forward in coupling atmospheric and ionospheric processes.

The possibility of initiation of electric discharges by a crossbow bolt (projectile) moving in the electric field of a cloud of negatively charged water droplets has been demonstrated for the first time [1]. Over one hundred of discharges have been produced. For each event, a high-speed video camera recorded the images of upward positive leaders developing from both the nearby grounded sphere and the projectile, followed by the return-stroke-like process. Corresponding currents were measured and integrated photos of the events were obtained. The results can help to improve our understanding of lightning initiation by airborne vehicles and by a vertical conductor rapidly extended below the thundercloud in order to trigger lightning with the rocket-and-wire technique.

We have observed unusual plasma formations (UPFs) in artificial clouds of charged water droplets using a high-speed infrared camera operating in conjunction with a high-speed visible-range camera. Inferred plasma parameters were close to those of long-spark leaders observed in the same experiments, while the channel morphology was distinctly different from that of leaders, so that UPFs can be viewed as a new type of in-cloud discharge. These formations can occur in the absence of spark leaders and appear to be manifestations of collective processes building, essentially from scratch, a complex hierarchical network of interacting channels at different stages of development (some of which are hot and live for milliseconds). We believe that the phenomenon should commonly occur in thunderclouds and might give insights on the missing link in the still poorly understood lightning initiation process.

The planetary boundary layer (PBL), which directly interacts with the underlying surface, differs significantly in its nature from the low-turbulent stably stratified free atmosphere. Fluctuations of the Earth’s surface heat balance immediately affect the PBL and assimilate there owing to the effective mechanism of turbulent heat transfer. In this case the upper boundary of the PBL plays the role of a cover, preventing the direct penetration of thermal effects and contaminants into an overlying atmospheric layer. In view of this, air pollution is especially dangerous when associated with shallow PBL. In addition, local peculiarities of climate change are mainly determined by the PBL height due to the high sensitivity of thin stably stratified PBLs to the thermal effects. Deep convective PBLs are not very sensitive to weak thermal effects, but they significantly affect the formation of convective cloudiness and the climate system as a whole by means of the turbulent entrainment of the thermal energy, humidity, aerosols, and other admixtures through the upper boundary. The PBL height and turbulent entrainment must be calculated when simulating and forecasting air pollution, abnormal frosts and heat, and other hazardous phenomena. In this paper we discuss the state-of-the-art knowledge in the area of PBL height simulation and suggest a new model of turbulent entrainment for convective PBLs.

The Global atmospheric Electric Circuit (GEC) is a fundamental coupling network of the climate system connecting electrically disturbed weather regions with fair weather regions across the planet. The GEC sustains the fair weather electric field (or potential gradient, PG) which is present globally and can be measured routinely at the surface using durable instrumentation such as modern electric field mills, which are now widely deployed internationally. In contrast to lightning or magnetic fields, fair weather PG cannot be measured remotely. Despite the existence of many PG datasets (both contemporary and historical), few attempts have been made to coordinate and integrate these fragmented surface measurements within a global framework. Such a synthesis is important elvinin order to fully study major influences on the GEC such as climate variations and space weather effects, as well as more local atmospheric electrical processes such as cloud electrification, lightning initiation, and dust and aerosol charging. The GloCAEM (Global Coordination of Atmospheric Electricity Measurements) project has brought together experts in atmospheric electricity to make the first steps towards an effective global network for atmospheric electricity monitoring, which will provide data in near real time. Data from all sites are available in identically-formatted files, at both one second and one minute temporal resolution, along with meteorological data (wherever available) for ease of interpretation of electrical measurements. This work describes the details of the GloCAEM database and presents what is likely to be the largest single analysis of PG data performed from multiple datasets at geographically distinct locations. Analysis of the diurnal variation in PG from all 17 GloCAEM sites demonstrates that the majority of sites show two daily maxima, characteristic of local influences on the PG, such as the sunrise effect. Data analysis methods to minimise such effects are presented and recommendations provided on the most suitable GloCAEM sites for the study of various scientific phenomena. The use of the dataset for a further understanding of the GEC is also demonstrated, in particular for more detailed characterization of day-to-day global circuit variability. Such coordinated effort enables deeper insight into PG phenomenology which goes beyond single-location PG measurements, providing a simple measurement of global thunderstorm variability on a day-to-day timescale. The creation of the GloCAEM database is likely to enable much more effective study of atmospheric electricity variables than has ever been possible before, which will improve our understanding of the role of atmospheric electricity in the complex processes underlying weather and climate.