Home – Home – Jornals – Atmospheric and Oceanic Optics 2024 number 1

High-resolution spectra corresponding to the rotational and the ν₂-ν₂ bands of the two most abundant isotopic species of ozone with one heavy ¹⁸O oxygen atom were recorded using SOLEIL synchrotron radiation source in the range 30-200 cm^-1. Additionally, the ν₂ vibrational-rotational bands were recorded between 550 and 880 cm^-1 using a classical glowbar source that made it possible to extend and refine information compared to published data on the observed transitions of these bands. The analyses of recorded spectra permitted us to deduce experimental set of energy levels for the ground (000) and the first bending (010) vibrational states, which significantly exceeds literature data in terms of rotational quantum numbers. For both isotopic species, the weighted fits of all experimental line positions were carried out including previously published microwave data. As a result of this work, the improved values of rotational and centrifugal distortion parameters for the states (000) and (010) were obtained that permitted modelling the experimental line positions with a weighted standard deviation of 1.284 (2235 transitions) and 0.908 (4597 transitions), respectively, for ¹⁶O¹⁶O¹⁸O, and 1.168 (824 transitions) and 1.724 (2381 transitions) for ¹⁶O¹⁸O¹⁶O.

Room-temperature cavity ring-down spectra (CRDS) of hydrogen sulfide were recorded at three pressures of 10, 20, and 30 Torr in the 12950-13300 cm^-1 range with a sensitivity on the order of 3 × 10^-11 cm^-1 in terms of the absorption coefficient and analyzed. The line positions and intensities are derived from these spectra. The theoretical simulation of these spectra was performed within the method of effective operators. The measured line positions and intensities are compared with the variational calculated values. Considerable difference between calculated ( Azzam A.A.A., Yurchenko S.N., Tennyson J., Naumenko O.V. Exomol line lists XVI: A hot line list for H₂S // Mon. Not. R. Astron. Soc. 2016. V. 460. P. 4063-4074) and observed line positions and intensities is found.

For the first time with high spectral resolution (0,00016 cm^-1) and threshold sensitivity (~ 1E-26 cm/molec.), the absorption spectrum of the H₂S molecule was recorded in the spectral ranges 6227.506-6236.844 and 6244.188-6245.348 cm^-1 at room temperature and pressures of 0.001-0.06 atm. The measurements were carried out at the Institute of General Physics on a high-sensitivity high-resolution diode laser spectrometer with a signal-to-noise ratio of more than 10000. Line center shift coefficients Δ₀/ P and collisional widths Г₂/ P have been estimated for the first time; new spectral lines have been recorded. The estimates of the experimental values of the positions of the line centers determined in this work differ from the calculated positions of the centers in the HITRAN database by the value Dν = (ν_H - ν_exp) × 10³ cm^-1 ≈ 0.001-0.01 cm^-1. The intensity estimates coincide much worse, the relative differences 100% × ( S_H - S _exp)/ S_H amount to tens of percent, the intensities of five lines differ by hundreds of percent or more.

The problem of controlling the parameters of the filamentation region of high-power femtosecond laser pulses for amplitude modulation of radiation by a metal mesh mask is theoretically considered. To this end, the initial laser beam is split into individual lower energy subbeams. This leads to a pronounced regularization of the spatial structure of the filaments, which is formed at the stage of radiation self-focusing due to diffraction interaction between subbeams in a nonlinear medium. Generally, the total length of the filamentation domain of femtosecond laser radiation in air is reduced when using modulation meshes. At the same time, the longitudinal continuity of laser plasma in such filaments can significantly increase. We show that the spatial parameters of filaments (coordinate of the start, length, and continuity) can be controlled over a wide range by changing mesh parameters (crosshair thickness and cell size), as well as the position of the mesh mask relative to the laser beam center. The results are important for predicting the propagation of high-power femtosecond laser radiation in a nonlinear medium, in particular, along atmospheric paths.

Transit observations of exoplanets make it possible to measure temperature and relative abundance of various elements in their atmospheres. The infrared line of metastable helium HeI 10830 Å is widely used to study the atmospheres of exoplanets by the transit absorption method. The emission spectra of stars have a significant impact on the physical and chemical parameters of the upper layers of the atmospheres. In this paper, we consider the features of absorption in the helium line for stars of different spectral classes by numerical simulation. The results show the key role of the star's emission spectrum in the formation of the upper atmosphere and in the amplitude of transit absorption of exoplanets in the HeI 10830 Å line.

Tundra lakes are an important indicator of climate change; therefore, the analysis of the dynamics of their size is of particular interest. This paper presents the results of using the U-Net convolutional neural network for tundra lakes segmentation in satellite optical images using Landsat data as an example. The comparative assessment of segmentation accuracy is performed for the original U-Net design and its modifications: U-Net++, Attention U-Net, and R2 U-Net, including with weights derived from a pre-trained VGG16 network. The segmentation accuracy is assessed based on the results of manual mapping of tundra lakes in northern Siberia. It is shown that more recent U-Net modifications do not provide a practically significant gain in segmentation accuracy, but increase the computational costs. A configuration based on the classic U-Net gives the best result in most cases (the average Soerens coefficient IoU = 0.88). The technique suggested and the resulting estimates can be used in analysis of modern climate trends.

We estimate the long-term variability of the parameters of single-layer cloud fields over the territory of Western Siberia in winter for the period from 2001 to 2019 based on MODIS data. The main idea of the applied method is to use the results of recognition of 11 cloud types from daily winter (December, January, and February) daytime satellite images. Features of single-layer clouds are considered for three latitudinal zones of Western Siberia: southern (< 60° N), transitional (60-65° N), and northern (> 65° N). We found linear trends for the following parameters of different cloud types: the coverage fraction of the target zones, optical thickness, effective particle radius, waterpath, and top height. The paper discusses the results of comparing the data we obtained with information from the annual Roshydromet assessment reports. We propose hypotheses about the reasons for the anomalous parameter values in the time series for different cloud types in the latitudinal zones of Western Siberia under study in winter.

In continuation of the first part of the work, experimental results of Kelvin-Helmholtz wave sounding with an UV BSE-5 lidar (355 nm), with the sensitivity higher than that of BSE-4 lidar (532 nm), are presented. Experiments on atmospheric sounding with the BSE-5 lidar were carried out in the winter-spring period over a built-up area, which is a “heat island". Improved lidar parameters in combination with thermal conditions in the atmospheric boundary layer, which is mainly stable stratified in the cold season, enables us to acquire new data on the shape of Kelvin-Helmholtz waves. It is ascertained that echo signals in both receiving channels of the lidar decrease by 30% after a sounding laser beam passes a turbulence intensity peak at the top of the wave arc. This effect of the atmosphere on echo signals of the turbulent lidar can be explained by beam broadening due to multiple scattering on random inhomogeneities of the medium.

The possibilities of using molecular scattering to determine the wind speed from measurements by a pulsed coherent Doppler lidar (PCDL) from an aircraft at altitudes from 10 to 20 km are numerically studied. The simulation was carried out for probing radiation focused at 500 m at wavelengths of 1 mm and 2 mm, the aperture diameter of the receiving-transmitting telescope was set equal to 10 cm. It is shown that the threshold SNR in measurements from an aircraft is attained at a pulse energy much lower than when sounding from the Earth. Modern PCDLs with probing pulse energies of 1-4 mJ, after adding a molecular scattering recording channel, can be used for airborne wind measurements at altitudes of 10-20 km.

Based on the multiyear expedition studies in the Kara Sea basin (11 expeditions in 2007-2022), we presented for the first time a statistical generalization of the atmospheric aerosol characteristics: the volume contents of submicron and coarse aerosol ( V_f и V_с ), the black carbon concentrations (еВС) and the spectral aerosol optical depth (AOD) of the atmosphere. Increased content of submicron and absorbing (eBC) aerosol was clearly manifested in the average spatial distribution in the southwestern part of the Kara Sea and minimal content in the northern part. The difference in the average concentrations V_f and еВС between these regions is 30-60%. The average aerosol characteristics for the entire Kara Sea had been: the atmospheric AOD (0.5 mm) was 0.043 at the Ångström exponent 0.8; the concentrations еВС were 22.8 ng/m³; and the particle volumes V_f and V_с were 0.26 and 1.39 μm³/cm³ respectively. The average concentrations V_f and еВС over the Kara Sea are shown to be intermediate between the data from the “Cape Baranov” and the Barents Sea.

Seasonal variability of the vertical distribution of chlorophyll a concentration, coefficients of spectral light absorption by optically active components of water and, spectral downwelling irradiance has been investigated in coastal waters of the Black Sea near Sevastopol in 2022-2023. Concentration of phlorophyll a in euphotic zone was minimal in winter (0.66 mg/m³) and maximal in spring (3.57 mg/m³). It has been revealed that colored dissolved organic matter was dominated in absorption at 438 nm in all the seasons. It was noted that the relative contribution of phytoplankton to the total non-water light absorption by all optically active components at 438 nm was the highest in summer. It has been shown that an increase in the total light absorption by suspended and dissolved organic matters led to a narrowing of the euphotic zone and a change in the spectral features of downwelling irradiance. Vertical distribution of Tchl- a and optically active components was associated with hydrophysical characteristics of waters.