Home – Home – Jornals – Atmospheric and Oceanic Optics 2026 number 5

This article addresses the problem of line identification in high-resolution vibrational-rotational spectra. We suggest an approach based on heuristic search applied in artificial intelligence systems for automatically identifying a set of molecular energy levels observed in a spectrum. Such systems solve the problem of finding a sequence of operations for transforming input data (formulas, knowledge) that brings the data to a certain target or desired state. The proposed approach simultaneously analyzes several rotational sublevels in a spectrum, thus enabling more reliable identification of the corresponding spectral lines using more information. The results can be used in optical atmospheric measurements and molecular physics.

Modern databases such as HITRAN and GEISA provide spectral line parameters only for Voigt profile (VP) calculations. Spectral modeling for describing various processes in many areas of chemistry, physics, earth sciences, and engineering uses this line profile for collisional isolated transitions. However, the use of VP leads to high errors as compared to high-precision experimental spectra. More sophisticated models have been developed for spectral modeling that take into account “non-Voigt" effects, such as changes in molecular velocity due to collisions and the velocity dependence of the broadening and shift coefficients during collisions. In this paper, we present the results of high-precision measurements and analysis of the absorption spectra in ¹²C¹⁶O in the pressure range from 0.001 to 0.3 atm using “non-Voigt” profiles. We analyze the pressure dependences of parameters of VP, RP, qSDVP-Δ₂, qSDVP, and qSDRP profiles of the P3-P8 lines of ¹²C¹⁶O. We show that the intensity S and the profile parameters Γ₀ and Δ₀ linearly depend on pressure, regardless of the profile type. The intensities S and the broadening Г₀/ P _CO and shift Δ₀/ P _CO coefficients for the profiles qSDVP-Δ₂ and qSDVP coincide with the experimental accuracy. Calculations using the VP demonstrate deviations of S , Г₀/ P _CO, and Δ₀/ P _CO values from the results for qSDVP-Δ₂ and qSDVP within 1-2%. A nonlinear dependence of Г₂ and Δ₂ on pressure is observed when using qSDVP-Δ₂, qSDVP, and qSDRP. The applicability limits of the profile models for describing high-precision experimental spectra of ¹²C¹⁶O molecule are estimated.

Optical radiation propagating in the atmosphere is partially absorbed by air, thus heating it; at the same time, an optical radiation beam acts as a linear extended heat source. The resulting convective phenomena contribute to atmospheric turbulence. Indoors, this convective turbulence has features related to spatial limitations and the presence of other heat sources. In this paper, convective air motions in a vicinity of a group of linear extended optical sources in a horizontal configuration of an open-side room under external wind influence are studied by numerically solving three-dimensional Navier-Stokes equations. To parallelize the calculations, a computing cluster with MPI interface was used. Convective cells arising along inclined optical beams and the corresponding velocity and temperature fields are described. It was found that the shape and location of the cells are determined by the inclination of beams optical axis and the configuration of the room. The evolution of temperature and velocity fields is shown. Spatial spectra of temperature fluctuations in various directions, including in the vicinity of optical paths, are constructed. The causes are described and the mutual effects of the beams are estimated upon changes in the structural characteristic of air refractive index fluctuations in the vicinity of inclined optical paths. The influence of the external wind on the thermal traces of optical radiation beams inside and outside the room is considered. Upon completion of the numerical experiment, there is a turbulence inside the room with spectrum of temperature fluctuations similar to Kolmogorov spectrum. The considered situations can be observed in specialized rooms of optical systems when air is heated by optical radiation of varying intensity. The resulting turbulence fields of convective and dynamic nature significantly impact the operation of recording devices. The results are important for predicting the correct operation of such devices and for evaluating the mutual influence of optical beams.

A specific feature of surface layer electricity research is the requirement for synchronized measurements and subsequent data interpretation to accurately distinguish and evaluate the impact of local disturbances and global electric field variations on observed electrical characteristics. To address the challenge of interpreting atmospheric electricity measurements, a mathematical model is required to establish a definitive link between global and local disturbances and the measured values. This paper presents a potential implementation of such a model in the form of a total current equation describing the daily dynamics of the electric field intensity in the surface air layer. The spatiotemporal structure of the turbulent surface air layer, which is formed under the influence of a global unitary variation in the ionospheric potential and a local turbulent generator with independent daily dynamics, has been studied. The work generalizes studies of daily variations in the electric field strength of the surface layer for the cases of constant total current at the upper boundary of the surface layer. The profiles of electric field strength, conduction current density, and turbulent current density at different times during the day were calculated. Their dependence on the degree of turbulent mixing in the surface air layer has been established. The calculation results can be useful in analyzing data from ground-based atmospheric-electric observations.

Spatial irradiance is a defining characteristic of radiation during the thermal impact of a laser beam on biological tissues, powders, and other scattering media. The provides a theoretical consideration of multiple light scattering in the volume of a semi-infinite diffuse scattering medium (DSM). Calculations are made for pressed dielectric powders with refractive indices n = 1.47, 1.72, and 2.00 at a wavelength of 1.06 μm (the first harmonic of a neodymium laser). The diffuse reflectance coefficients ρ(1 - Λ) calculated by the Monte Carlo method and in the Kubelka-Munk approximation are compared. A linear relationship is established between the spatial irradiance in DSM volume and the diffuse reflectance coefficient. The precisions and applicability limits of the original and corrected Kubelka-Munk formulas are determined. A complex relationship is ascertained between the single scattering albedo Λ and the angular dependence of a photon flux incident on the DSM-air interface f (α). In particular, it was shown that for Λ → 1 and isotropy scattering, f (α) = cos(α), where a is the photon incidence angle. The results can be used for the development of methods for determining spatial irradiance and, for example, in laser medicine.

Laser-induced plasma diagnostics in aerosols is complicated by plasma inhomogeneity. In this work, the electron density of laser-induced plasma was evaluated based on Ba II 455.4, Na I 589, Al I 396.2, Ca II 393.4 and Fe I 542.4 nm emission lines for the case of using equipment on mobile carriers. It was found that the electron density is minimal for the Ba II line and maximal for the Na I line; the difference in the values attained almost an order of magnitude, which was attributed to differences in the diffusion lengths of the elements. It was experimentally shown that the plasma electron temperature weakly depends on time in the 2-4 ms range at exposure times of 40 and 150 ms. It was confirmed that recombination pumping of the upper levels of transitions under study did not significantly affect the intensity of the analytical lines. Based on the analysis of the rate constants of excitation from the ground state, the limit of detection was found to be the worst for Al I 396.2 nm line. The results of the work can be used in emission spectral analysis of aerosols.

The onset of polar stratospheric cloud (PSC) formation and chlorine activation is so far considered to be the temperature threshold of formation of nitric acid trihydrate T _NAT, below which the HNO₃ concentration sharply increases in PSC particles. In this paper, we use the data on the minimal temperature, maximal negative deviations of ozone concentration from multiyear average, and maximal nitric acid (HNO₃) concentration in the Arctic stratosphere at four sites: Eureka, Canada (EUR); Ny-Ålesund, Norway (NAD); Thule, Greenland (THU); and Resolute, Canada (RES) for calculations of the maximal HNO₃ concentrations and the total HNO₃ columns. The maximal HNO₃ concentrations decrease throughout the winter until late February at all observation sites considered here due to condensation of gas-phase HNO₃ on PSC particles. The concentrations start to grow after return of sunlight to polar latitudes due to PSC sublimation and HNO₃ export from peripheral areas of the vortex during its deformation. The HNO₃ content in the winter-spring stratosphere of the Arctic is an important indicator of the PSC formation and breakup.

The analysis of statistical properties of aerosol density fluctuations can serve a starting point for the study of the random component of wind velocity field. In this paper, we analyze the fluctuations of power of a scattered signal measured by an airborne lidar in the DELICAT (DEmonstration of LIdar based Clear Air Turbulence detection) project experiment. A new method for the study of aerosol clouds based on 2D Fourier transform was proposed. Flight segments with constant altitude, direction, and velocity of aircraft were selected for the analysis. A signal was considered in the coordinate system with the abscissa axis representing the distance from the aircraft to a scattering volume and the ordinate axis representing the aircraft path relative to air mass. In these coordinates, aerosol clouds appear as stripes inclined at an angle of 45°. Spatial spectra of aerosol density fluctuations are obtained. For areas where aerosol is observed, 2D spectra have a peak in the vicinity of the main diagonal of the frequency plane. Their diagonal sections are equal to estimates of 1D spatial spectra of aerosol concentration fluctuations within the following approximations: 1) clouds are stationary on a time scale on the order of 1 min, 2) variations in the direction of the sounding line are negligibly small. The slope of 1D spectra has been estimated.

The study of the propagation of high-power ultrashort pulses in the atmosphere is an urgent problem in optics and laser physics. In this paper, we consider the conditions for modifying the basic sensing equation using supercontinuum radiation concentrated in postfilament channels associated with nonlinear foci and filamentation zones of a high-power femtosecond laser pulse. A method for determining the attenuation coefficient is proposed, similar to the well-known logarithmic derivative method used in single-frequency laser sensing. As an example, for a layered homogeneous non-absorbing medium in the single-scattering approximation, the attenuation coefficient is found using radiation at the wavelengths of the supercontinuum concentrated in postfilament channels formed in two spatially spaced nonlinear foci. It is concluded that the modified sensing equation for spatially spaced nonlinear foci is promising for evaluating the effectiveness of broadband optoelectronic communication systems, location detection, and rangefinding.

The problem of air pollution in Crimea is of interest due to its geographical characteristics and resort use. Experimental studies on the composition and temporal variability of aerosols in the surface air layer were conducted in the southeastern part of the Crimean Peninsula at the background environmental monitoring station of T.I. Vyazemsky Karadag Scientific Station - a nature reserve of the Russian Academy of Sciences, a branch of the Federal Research Center of the Southern Oceanological Institute, from March 21 to June 17, 2020. For the first time, data are presented on temporal variations in the daily average mass concentration of aerosol, chemical elements in its composition, and aerosol particles of 0.15-1.5 mm and 0.2-5.0 mm in size. Concentrations of 25 selected chemical elements were determined. The comparison was made between the elemental composition of the aerosol and its size distribution, meteorological conditions, and the direction of long-range transport of air masses. The size of particles transporting heavy metals and metalloids (Zn, Mo, Cd, Pb, Bi, Se, Sn, and Sb), as well as elements of global origin was determined. The elements S, Cu, and Hg, for which no significant correlation with particle size was found, are likely of mixed origin due to competition between natural and anthropogenic sources in different periods. The results characterize the aerosol parameters during the spring-summer period in the eastern part of Crimea and are of interest to specialists involved in environmental monitoring in the resort and recreational region.

To better understand the current trends in the growth of greenhouse gas concentrations on a regional scale, it is necessary to analyze their isotopic composition in order to identify their sources and sinks, which determine both seasonal and long-term changes in their atmospheric content. Continuous observations of atmospheric CO₂ and CH₄ and the carbon isotope composition of their molecules carried out in 2022-2024 at the Fonovaya observatory enabled the range of background values and seasonal pattern of δ¹³C-CO₂ and δ¹³C-CH₄ in the atmosphere of the southern taiga zone of Western Siberia to be determined. The average daytime (01-05 pm) values of δ¹³C-CO₂ and δ¹³C-CH₄ varied in the ranges -9.2 to -5.7‰ and -51.7 to -46.5‰, respectively. The analysis of background values revealed a sharp summer minimum in CO₂ concentration and, conversely, a maximum in δ¹³C-CO₂, indicating intensive uptake of ¹²CO₂ by the regional terrestrial ecosystems. Winter values of both CO₂ concentration and δ¹³C-CO₂ are consistent with data from other greenhouse gas monitoring stations in the Northern Hemisphere. The pattern of seasonal variations in atmospheric CH₄ mixing ratios and δ¹³C-CH₄ values in the region under study indicates that the winter maximum in CH₄ content is driven by anthropogenic factors, while the summer maximum, by the predominance of biogenic methane emissions from Western Siberian wetlands. Using the Keeling plot method, source/sink signatures influencing changes in atmospheric CO₂ and CH₄ concentrations in the area under study were determined for each month of the year. The results can be used when analyzing and interpreting long-term observations of greenhouse gases in Siberia.