Home – Home – Jornals – Atmospheric and Oceanic Optics 2025 number 4

Currently, many studies are aimed at increasing the information capacity of data transmission channels by using the orbital angular momentum (OAM) of laser beams to encode information. The use of this approach in atmospheric optical communication systems is limited by the distorting effect of atmospheric turbulence, which makes decoding difficult and reduces the data transfer rate. In addition, the intensity distributions of vortex beams with opposite in sign OAM values are identical in the case of homogeneous media, which limits the use of the OAM sign for encoding information. The main goal of the study was to evaluate the fundamental possibility of using neural networks to recognize opposite in sign OAM values of vortex beams in a turbulent atmosphere only through intensity images. The study is based on numerical simulation of the Laguerre-Gauss beam propagation in a turbulent atmosphere and further use of the obtained intensity images for training and testing neural networks. It has been shown for the first time that the use of neural networks makes it possible to recognize opposite in sign OAM values of Laguerre-Gauss beam through intensity images in case of propagation in a turbulent atmosphere with an accuracy of more than 90%. The obtained results can be useful for developers and researchers of atmospheric optical communication systems using OAM of vortex beam.

To form plasma antennas in various radio and telecommunication devices it is necessary to increase the relaxation time of laser breakdown centers. To overcome this problem, the processes occurring in aerodisperse media containing solid microparticles during interaction with laser radiation are considered. The decay times of plasma with aerosol particles under the influence of nanosecond and microsecond laser pulse have been analyzed. The influence of the electron shell around solid microparticles on the creation of a continuous ionization zone in the aerosol atmosphere formed by overlapping plasma halos around microparticles has been evaluated. The conditions necessary for the creation of a long ionized channel formed by breakdown centers during explosive evaporation of atmospheric microparticles in the zone of influence of a nanosecond pulse of a CO₂ laser and further maintenance of the formed plasma by the radiation of a microsecond laser are considered. A scheme of an experimental setup for creating a long ionized channel in an aerosol atmosphere is suggested. The results can be used for creation of wireless communication channels in the atmosphere.

The sulfur dioxide (SO₂) plays a key role in the winter-spring stratosphere of the Arctic because the sulfur compounds SO₂ and H₂SO₄ (together with nitric acid HNO₃) are the primary construction materials going to form the polar stratospheric clouds (PSCs). This paper studies the maximal SO₂ concentrations and total SO₂ columns at four Arctic sites: Eureka (Canada), Ny-Ålesund (Norway), Thule (Greenland), and Resolute (Canada) based on data on the minimal temperature, maximal negative deviations of ozone concentration from multiyear average, maximal sulfur dioxide concentration in the Arctic stratosphere, and the total ozone and sulfur dioxide columns calculated from the corresponding altitude profiles. The temperature and ozone mixing ratio profiles are obtained from the Aura MLS observations for 2005-2022; the sulfur dioxide mixing ratio profiles are calculated from Aura MLS observations for 2010/11, 2019/20, 2020/21, and 2021/22. The results can be useful for studying of how SO₂ affects the PSC formation and O₃ destruction in the winter-spring stratosphere of the Arctic.

The article is devoted to experimental study of hyperspectral method of detection of oil pollution on the earth surface in the near-IR range. The results of experimental measurements of spectral brightness coefficient of soil samples contaminated with various types of petroleum products in the spectral range 1.6-2.5 mm are given. The influence of soil moisture and rainfall on the spectra of reflection of soils (various types of sand and soil from forest and park areas) contaminated with petroleum products (Moscow and Samara oil processing plants, kerosene, gas condensate, various gasoline brands, motor oils, and diesel fuel) was studied. It was shown that spectral notches of about 1.73 and 2.3 mm (typical for soils contaminated with oil products) in most cases remain in the spectra of reflection under conditions of moderately wet soil, moderate “rain”, and even heavy “rain”. The results of the work of the created neural network show the probability of detecting oil pollution on the earth surface to be more than 99% under conditions of moderately moist soil and moderate “rain” and more than 88% under conditions of heavy “rain” and wet soil for 14 spectral channels with a resolution of 10 nm in the range 1.6-2.4 mm.

The NH Earth polar stratospheric vortex significantly varies from year to year in winter, which periodically lead to the occurrence of sudden stratospheric warmings (SSWs). Such events significantly disturb the circulation and chemical composition of the polar stratosphere. Our understanding of the wave processes that are recorded in the stratosphere and are directly involved in the occurrence of SSWs remains incomplete to date. Oscillations of the polar stratosphere of the Northern Hemisphere in the period from 1979 to 2023 are studied based on ERA5 reanalysis data. The method of current spectra is used to study the variability of the periodicity of wave processes in the polar stratosphere for different time intervals. As the main indicator of the wave properties of the stratosphere, we use the field of the vertical component of the wind speed in the region between 60 and 90° N. It is shown that in some years, oscillations of the stratosphere coincide with or are close to the periods of the main waves of the fortnightly and monthly lunar gravitational tide. The causes and consequences of the oscillatory processes synchronization in the polar stratosphere with the lunar gravitational tide are discussed. The results can be useful for improving the understanding of the mechanisms of occurrence of SSWs, as well as for improving the forecast of such events.

The paper evaluates the experience of creating a regional monitoring system for the turbulent energy exchange of the atmosphere with the underlying surface. An original technology for building an observation network based on ultrasonic automatic weather stations of domestic production has been developed. Based on the developed technology, the TomskFluxNet system has been deployed in Tomsk - the first urban network of observations of the characteristics of turbulent energy exchange of the atmosphere with the surface in Northern Eurasia with a pronounced continental climate. The first experimental results were obtained, on the basis of which significant differences in turbulent heat and momentum flows over urban and natural underlying surfaces were revealed. The results can be used to verify and improve the parameterization of the urban surface, which are actively developing in land-air models and weather forecast.

In 2023, more than a third of dangerous meteorological events in the Siberian Federal District were associated with strong winds, which underscores the importance of improving the accuracy and timing of its forecasting. Modern numerical simulation and machine learning methods make it possible to improve forecasts, but the task of directly calculating wind gusts remains relevant due to the limited resolution of models. An original method is proposed for correcting the results of short-term forecast of wind gusts obtained on the basis of mesoscale models of numerical weather forecasting using advance measurements and artificial neural networks. The results show that the proposed correction method makes it possible to improve the forecast of wind gusts by various semi-empirical methods. The results can be applied in meteorology, energy, transportation, and other industries to minimize damage from dangerous weather events.

The two-pulse synchronous excitation method used for remote laser diagnostics of matter has recently attracted great interest, since it significantly expands the capabilities of traditional methods of single-pulse laser action. However, the practical implementation of the method requires strict synchronization of the instants of sending laser pulses and automated control of their time positions. Obviously, the two-pulse excitation scheme needs in more complex equipment and complicates the application of the method. The use of standard laser trigger and control tools is expensive and cumbersome and not always applicable. The article presents the specialized system for triggering laser pulses with a capability of recording the shape and position of excitation pulses with their subsequent display on a single time scale. A structural diagram and technical characteristics of the device are given. An example of using the laser trigger system to ensure the operation of a research stand for remote laser detection of organophosphorus compounds by the two-pulse laser fragmentation method of laser-induced fluorescence (LF/LIF method) is described. The developed synchronization system can be used in optical diagnostic methods, where synchronous action of two or more independent laser sources is required, to set and control the time delay between their optical pulses.

Photodissociation lasers on alkali metal halide vapors emit at the first resonance transitions of atoms. This allows using such lasers for the analysis of a number of metals in gaseous media by the absorption and resonance fluorescence method. In the first part of the work, the general principles and mechanisms of creating inversion at resonance transitions of alkali metal atoms during photodissociation of their halide molecules are considered. Data on wavelengths at the first resonance transitions of alkali metal atoms (Li, Na, R, Rb, Cs) are systematized. The main processes responsible for the formation of the spectral contour of resonance generation lines of photodissociation lasers are determined. Some features of the application of such lasers for sounding gaseous media are noted. The results can be used in the study of photodissociation generation at the first resonance transitions of alkali metal atoms.

Alkali metal halide photodissociation lasers emit at the first resonance transitions of atoms. This allows using such lasers for the analysis of a number of metals in gaseous media by the absorption and resonance fluorescence method. In the first part of the work, the general principles and mechanisms of creating inversion at resonance transitions of alkali metal atoms during photodissociation of their halide molecules are considered. Data on wavelengths at the first resonance transitions of alkali metal atoms (Li, Na, R, Rb, Cs) are systematized. The main processes responsible for the formation of the spectral contour of resonance generation lines of photodissociation lasers are determined. Some features of the application of such lasers for sounding gaseous media are noted. The results can be used in the study of photodissociation generation at the first resonance transitions of alkali metal atoms.

Theoretical studies of the ways of increasing the efficiency of second harmonic generation (SHG) in visible lasers are relevant because of common use of UV radiation in different scientific and engineering problems. The work compares three most common approaches to second harmonic generation: SHG(L), where laser radiation (LR) is guided directly into a crystal (without additional optics); SHG(F), where LR is focused into a crystal by a spherical lens; and SHG(T), where LR is compressed by a lens (or mirror) telescope before entering a crystal. The SHG efficiency is shown to be maximal at optimal transverse size of LR in a crystal, which depends on LR amplitude profile in a cross section. When SHG is implemented under near-optimal conditions, SHG(F) is the most effective. If the transverse size of LR in a crystal is noticeably larger than optimal, SHG(F) is the least effective. It is shown that the gain in SHG efficiency, which is provided by replacing a long-focus lens with a suitable telescope, can exceed 100% with an increase in the transverse size of LR in a crystal and for super-Gaussian beams. In the first part of this paper, all the results are obtained in the preset field approximation. The refined results (with a strict solution of a set of nonlinear wave equations) will be presented in the second part. The results of the study can be useful for developing efficient frequency converters for metal vapor lasers.