Search

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.

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).

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.

Sensitivity of the global electric circuit (GEC) to variations of atmospheric conductivity and current sources is analyzed and discussed. When the undisturbed exponential conductivity profile is assumed all over the Earth, the most substantial changes in the ionospheric potential (IP) are caused by conductivity perturbations inside thunderstorms; if, in addition, conductivity reduction inside thunderstorms and nonelectrified clouds is assumed, the IP becomes less sensitive to conductivity perturbations; besides, the IP is even more sensitive to source current variations than to conductivity. Current source and voltage source descriptions of GEC generators are compared; it is shown that the IP variation may critically depend on the chosen description. As an application, the IP variation due to nuclear weapons testing is studied; it is shown that neither local nor global increase of conductivity in the stratosphere could alone explain the observed 40% IP increase in the 1960s; at the same time this increase might be accounted for by a 40% increase in the source current density or a 46% reduction of the conductivity inside thunderstorms, provided that it was not reduced initially. The IP variation due to solar activity and, in particular, due to solar modulation of galactic cosmic ray flux is also discussed and modeled, which required an adequate parameterization of the rate of atmospheric ion pair production over the solar cycle. It is estimated that the maximum IP variation on the scale of the solar cycle does not exceed 5% of the mean value, unless source current perturbations are taken into account.

[1] Light detectors sensitive to wavelength ranges 240–400 nm and beyond 610 nm (which we refer to, for simplicity, as the UV and Red bands) on board Universitetsky-Tatiana-2 satellite have detected transient flashes in the atmosphere of duration 1–128 ms. Measured ratio of the number of Red photons to the number of UV photons indicates that source of transient radiation is at high atmosphere altitude (>50 km). Distribution of events with various photon numbers Qa in the atmosphere found to be different for “luminous” events Qa = 1023 – 1026 (with exponent of differential distribution –2.2) and for “faint” events Qa = 1021 – 1023 (with exponent − 0.97). Luminous event parameters (atmosphere altitude, energy released to radiation, and temporal profiles) are similar to observed elsewhere parameters of transient luminous events (TLE) of elves, sprites, halo, and gigantic blue jets types. Global map of luminous events demonstrates concentration to equatorial zones (latitudes 30°N to 30°S) above continents. Faint events (with number of photons Qa = 1020 – 5⋅ 1021) are distributed more uniformly over latitudes and longitudes. Phenomenon of series of transients registered every minute along satellite orbit (from 3 to 16 transients in one series) was observed. Most TLE-type events belonged to series. Single transients are in average fainter than serial ones. Some transients belonging to series occurs far away of thunderstorm regions. Origin of faint single transients is not clear; several hypothetical models of their production are discussed.

The first results obtained through the university small satellites program developed at Moscow State University (MSU) are presented. The space environment was investigated aboard two MSU microsatellites designed for scientific and educational purposes, Universitetsky-Tat’yana and Universitetsky-Tat’yana-2. The scientific equipment is described to study charged particles in near Earth space and atmospheric radiations in ultraviolet, red, and infrared optical wavelength ranges. The dynamic properties of fluxes of charged particles in microsatellite orbits are studied and findings are presented regarding specific parameters of solar proton penetration during the geomagnetic disturbances. Experimental results are considered concerning flashes of ultraviolet (UV), red (R), and infrared (IR) radiation that are transient light phenomena in the upper atmosphere. The space educational MSU program developed on the basis of the Universitetsky-Tat’yana projects is reviewed.

This section focuses on the physical phenomena, leading to large-scale space-charge and electric field generation (electric dynamo) in the planetary atmospheres, and ways of their theoretical description. The main attention is paid to charge-layer formation in atmospheres. Under terrestrial conditions, a problem of charge-layer formation in the atmosphere is important from the viewpoint of both thunderstorm and fair weather electricity. It is important also for the problems of intense layer generation under perturbed ionization conditions, charge layer formation over deserts, high field generation in the mesosphere etc. On the other hand, charge-layer treatment allows verifying electrification theories being applied to more or less simple 1D conditions such as the electrode effect, cloud screening layers, long-term charge layers in mesoscale convective systems. The paper reviews the results of recent research in this field. General conditions of the electro-hydro-dynamic description and their applications to the planetary atmospheres are discussed in terms of the Debye length, mean free path length of charged particles, Langmuir frequency and electrical conductivity. In terms of electrostatic interaction energy, it is found that three phases for charge carriers co-exist in strongly electrified clouds in the Earth’s atmosphere. Crucial role of turbulent motion of conducting media for electric dynamo realization is revealed. The results of recent research in the modeling of the electrode effect, fog electrodynamics, screening layers in clouds and aerosol/dust structures, long-term charge layers in mesoscale convective systems are presented. Nonlinear solutions, demonstrating the formation of charge layers in planetary atmospheres, are examined.

Ultralow frequency pulsations of electric field in the surface atmospheric layer were investigated under fair weather conditions. A new method of structural-temporal analysis has been applied to the study of spatiotemporal structures of the electric field described previously by [Anisimov et al., 1994]. The method is based on exploration of the structural function by averaging the remote sensing data over respective temporal spans. This analysis allows quantitative estimations of spatial scales L ≃ 500 - 103 m and temporal scales not less than τ = 10 min for the structural elements of the planetary boundary layer electricity; we call these recently examined elements “aeroelectric structures” (AES). Quasiperiodic sequences and high-amplitude solitary AES have been recognized. Three-dimensional structural-temporal patterns are presented which directly characterize the level of electric energy perturbations connected with AES formation during night-day evolution. A model of AES formation has been developed, taking into account the occurence of convective cells with respective turbulent air and space charge density distributions that are transferred by the wind over the ground and cause the electric field fluctuations at the points of observation. Therefore formation of such submesoscale structures can be explained by the redistribution of space charge within the surface layer, with the structures of the smallest scales coupled to the turbulent mixing of the ions and aerosols. In addition to the advection and turbulent mixing of space charge, we also consider the cooperative electroaerodynamic effects which might occur in a system of bipolar ion and aerosol particles under the influence of a terrestrial electric field. We have proposed an advanced model treating the AES formation as the result of instability arising in such a system, taking into account the dependence of the effective ion-aerosol attachment coefficient on the external electric field strength.

[1] We present a new experiment on the detection of thunderstorm neutrons at orbital altitudes. The aims of the experiment called “Scafandr” are to establish the nature of the neutrons and to explore their properties. Also, the dosimetric measurement program is included in the experiment mission. For the neutron program, measurement of the thermal neutron fluxes from an altitude of 350 km down to 200 km is planned. We plan to obtain substantial statistics and resolution of neutron bursts. This will allow for mapping of the neutrons' distribution on the considered altitudes for their comparison with the thunderstorm activity maps and for comparison with the results of neutron burst numerical modeling. Previous experiments carried out are discussed, and their comparative analysis with the presented one is given.

[1] In this paper we perform a theoretical analysis of the direct passage of neutrons in the atmosphere from an altitude of about 5 km up to several hundred kilometers. We consider that these neutrons are generated during thunderstorms in what favor there is some experimental evidence. Two main mechanisms of the neutrons generation in thunderstorms appeared in the literature: the nuclear synthesis directly in the lightning channel and the photonuclear synthesis owing to production of gamma-rays by the runaway electrons. Both of them are discussed in the present work. For the qualitative analysis we considered the process of neutrons propagation in the atmosphere as consisting of three stages: initial neutron deceleration to thermal energies, then diffusion, and further free propagation. Absorption of neutrons was neglected. Also, in modeling the atmospheric matter only nitrogen and oxygen were considered as the main atmospheric components. With these conditions and taking into account the predicted parameters of the neutron generation source, it is shown that the estimated flux well corresponds to the known experimental results. On this basis the preferred mechanism of the neutron generation is indicated. For a more rigorous picture of the neutrons propagation, capable for description of the slowing down, thermalization, and diffusion processes, one has to perform a numerical calculation and for this we propose a computer simulation scheme based on the cellular automation method. The corresponding plain analysis of the neutrons passage confirms the estimation mentioned above. The proposed scheme can be used for modeling the real neutron source. On the basis of our results we discuss some characteristic features of the observed neutron fluxes. The obtained results are to be tested by the “Radioskaf” experiment based on the scientific device called “RAZREZ.” One of the experiment objectives is detection of neutrons with different energies at altitudes of 200–400 km aiming to reveal the nature and characteristics of the neutron radiation source.

[1] In Russia several space missions are now planned to study transient luminous events in the atmosphere and high-energy charged particles at satellite altitudes. The experimental goal is to investigate the origin of the high-energy electrons and gamma ray quanta for specific transient luminous events (TLEs) and their role in the ionosphere-magnetosphere system. Simultaneous measurements of electrons at the orbit of the satellite and TLE atmospheric radiation in many wavelength bands will be performed in two missions, Tatiana-2 and RELEC. In the TUS mission UV transient event detection will be accompanied by measurements of the weak UV emission from the “seed” electrons of extensive air showers of extremely high-primary energies.

[1] Computer simulations on transient luminous emissions in the mesosphere and lower ionosphere have been performed for realistic lightning modelings with fast-varying current surges (M components) superimposed on the lightning continuing current (CC). The algorithm used here is an electromagnetic (EM) code, which enables us to estimate self-consistently the reduced electric field, electron density, conductivity, and luminosity as a function of space and time by solving the Maxwell equations. It is found that M components in the CC with small amplitudes, but with a fast-varying EM effect, can initiate or enhance the occurrence of sprites. Even for a return stroke (RS) without CC, subsequent high-frequency current variations (like M components) are found to lead to dramatic changes in the sprite occurrence. The physics underlying these changes is studied by means of, e.g., temporal and spatial variations of luminosity, electron density, and conductivity. As the conclusion, the RS is a fundamental agency for spites, but high-frequency variations as EM effects exhibit an additional essential influence on sprite occurrence. These computational results are used to offer some useful ideas concerning the unsolved problems of sprites and halos, including polarity asymmetry, long-delay characteristics, and morphological shapes of sprites.

[1] A layered system of external currents is used to model the electric environment of a mesoscale convective system (MCS). The model takes into account the multilayer structure and appropriate horizontal scales of the MCS charge regions. The detailed model determines the electric field and current inside and in the vicinity of a stationary MCS as well as the net vertical current above the thunderclouds, which is an important measure of its contribution to the global electric circuit. The relatively large horizontal scale of an MCS ensures a more effective coupling to the ionosphere than for an isolated thunderstorm. In the model calculations the MCS-trailing stratiform region had a net vertical current magnitude of about 25 A versus only 0.4 A for a convective element of the MCS (which is similar to the contribution of an isolated thunderstorm). Additionally, it has been found that an MCS can serve either as an effective generator in the global circuit or as a discharger of it depending on the polarity, magnitude, and thickness of the layers of external current.

As a result of electric field measurements in remote points of the surface layer and analysis of obtained statistical characteristics (structural function, temporal spectra) two typical scales of electric field pulsations are found. The lowest one L0 ≃ 20–60 m coincides with an external scale of neutral gas turbulence under fair weather conditions. The highest scale L1 ≳ 60 m testifies to the existence of long-time electric field perturbations which lead to the anomalous growth of the structural function DE(r) at a distance r > L1. The relation between the scales L0 and L1 depends on the particular experimental conditions. The theoretical model for the function DE(r) has been developed, taking into account the turbulent mixing of charged particles and thermal convection in the surface layer. It is shown that the expression for DE consists of two parts. The first part describes fluctuations caused by the charge separation due to neutral gas turbulent mixing; the second part gives a contribution of large-scale convective cells, which can transfer a volume charge along the Earth's surface.

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.