Search

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.

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.

We analyze the formulation of the problem of global atmospheric electric circuit modeling. It was shown that under some relatively simple and widely used simplifying assumptions this problem can be reduced to finding the temporal and spatial dependencies of the electric potential on the specified generators, which are determined by the external electric current density. They correspond to thunderclouds in the real atmosphere. The ionospheric potential (the potential difference between the upper and lower atmospheric boundaries) is not specified explicitly but can be uniquely determined from the solution. The formulations of the stationary and nonstationary problems are given in terms of the potential and their well-posedness is discussed. We obtained a number of analytical relations under some restrictions on the distribution of conductivity. They include the formulas which explicitly express the ionospheric potential in terms of the problem parameters. The examples of numerical calculations using the software developed on the basis of general formulations of the stationary and nonstationary problems are demonstrated.

[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.

Millisecond ultraviolet (240–400 nm) and red-infrared (610–800 nm) flashes were detected in the nighttime atmosphere with the scientific payload installed onboard the Universitetsky-Tatiana-2 micro-satellite. Flashes with various numbers of photons, from 1020 to 1026, were detected within the atmospheric area 300 km in diameter observed by the detector. The flashes differ in duration and temporal profile: from single short flashes ∼1 ms in duration to flashes with a complex profile more than 100 ms in duration. Different global geographic distributions are observed for flashes with different numbers of photons. Flashes with fewer than 1022 photons are distributed uniformly over the Earth’s map. Flashes with more than 1022 photons are concentrated near the equator and above the continents. Series of flashes were observed in one turn of the satellite when flying not only over thunderstorm regions but also over cloudless ones. The flash number distribution has been derived from the ratio of the numbers of red-infrared and ultraviolet photons. As applied to discharges in the upper atmosphere, whose glow is dominated by the emission in the first and second positive systems of molecular nitrogen bands (1PN2 and 2PN2), this distribution is equivalent to the flash altitude distribution in the atmosphere. The observed ratio of the numbers of photons in red-infrared and ultraviolet flashes agrees with the calculated one for electric discharges at altitudes higher than 50 km. In-orbit measurements of the charged particle flux (with a threshold energy for electrons of 1 MeV) provide no evidence for a synchronous occurrence of an ultraviolet flash and a burst in the particle flux in the orbit.

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.

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.

[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] 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] Short-term (f ≃ 10−3–1 Hz) electric field pulsations in the surface atmospheric layer have been measured during 1999–2001 under the fair-weather and fog conditions. At the frequencies of 10−2–1 Hz these pulsations have a power-law spectrum with the spectral index varying in the range from −1.23 to −3.36 while the most probable values of the index fall into the range from −2.25 to −3.0, unlike the temperature fluctuation spectra which obey in the inertial subrange the Kolmogorov power law with the spectral index close to −5/3. Under the fog conditions the intensity of electric-field pulsations increases by about an order of magnitude compared to the fair-weather conditions. The relation of spectral characteristics to the formation of aero-electric structures (AESs) is evident; the spectral index distribution during AES flyby has two maxima. Analysis of the mechanisms explains the relationship between electric-field spectra and the neutral-gas turbulence and AES formation.

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 Pan-Eurasian Experiment (PEEX) is a new multidisciplinary, global change research initiative focusing on understanding biosphere-ocean-cryosphere-climate interactions and feedbacks in Arctic and boreal regions in the Northern Eurasian geographical domain. PEEX operates in an integrative way and it aims at solving the major scientific and society relevant questions in many scales using tools from natural and social sciences and economics. The research agenda identifies the most urgent large scale research questions and topics of the land-atmosphere-aquatic-anthropogenic systems and interactions and feedbacks between the systems for the next decades. Furthermore PEEX actively develops and designs a coordinated and coherent ground station network from Europe via Siberia to China and the coastal line of the Arctic Ocean together with a PEEX-modeling platform. PEEX launches a program for educating the next generation of multidisciplinary researcher and technical experts. This expedites the utilization of the new scientific knowledge for producing a more reliable climate change scenarios in regional and global scales, and enables mitigation and adaptation planning of the Northern societies. PEEX gathers together leading European, Russian and Chinese research groups. With a bottom-up approach, over 40 institutes and universities have contributed the PEEX Science Plan from 18 countries. In 2014 the PEEX community prepared Science Plan and initiated conceptual design of the PEEX land-atmosphere observation network and modeling platform. Here we present the PEEX approach as a whole with the specific attention to research agenda and preliminary design of the PEEX research infrastructure.