Atmospheric and Oceanic Optics最新文献

Cirrus clouds significantly affect the radiation budget of our planet and play an important role in climate formation. To study their optical properties, it is necessary to solve the problem of light scattering by nonspherical ice particles. This paper focuses on the numerical simulation of characteristics of light backscattering by hollow hexagonal columns by the physical optics method. We examine particles of 10 to 316 μm in size and wavelengths of 0.355, 0.532, and 1.064 μm. The findings reveal that the backscattering peak caused by corner reflection rapidly decreases as the cavity of hexagonal columns increases, then several secondary maxima of up to 10% of the main peak appear. The positions of these secondary maxima are independent of the particle size and incident wavelength, but strongly depend on the particle shape. These results are valuable for developing an optical model of cirrus clouds and for laser sounding of the atmosphere.

The results of describing the spatial distribution of methane concentration in the surface water of Lake Baikal in the spring are presented. The basis was the measurements of CH₄ content which were first carried out in the round-the-clock continuous mode along the entire route of the passage of research vessel in the complex expeditions of Limnological Institute, Siberian Branch, Russian Academy of Sciences, in the spring seasons of 2013, 2016, 2017, 2018, 2021, and 2022. Based on the results of six expeditions, a merged data array was compiled; it included 12 100 segments (with a step of 0.005° in latitude and 0.01° in longitude) which covered the total area 4466.7 km², or 14% of the surface of Lake Baikal. For a more detailed description of the spatial distribution of methane concentrations in surface water throughout the Baikal water area, the statistical characteristics were calculated in four zones: between 0 and 100 m, 100 and 200 m, 200 and 400 m, and over 400 m isobaths. The comparison of the methane concentrations in the analyzed array with the data of other researchers obtained in different years in nearby regions of the water area made it possible to conclude that the results presented in the work adequately reflect the most stable features of the spatial distribution of methane concentration in surface water of Lake Baikal in spring seasons.

The absorption spectrum of the H₂S molecule is recorded with high spectral resolution (0.00016 cm⁻¹) and threshold sensitivity (∼1E-26 cm/molec.) in the 6227.506–6236.844 and 6244.188–6245.348 cm⁻¹ spectral ranges at room temperature and pressures of 0.001–0.06 atm for the first time. The measurements were performed at the General Physics Institute, Russian Academy of Sciences, at a high-sensitivity high-resolution diode laser spectrometer with a signal-to-noise ratio of more than 10 000. Line center shift coefficients Δ₀/P and collisional widths Γ₂/P are estimated for the first time; new spectral lines have been recorded. The experimentally estimated line centers differ from the calculated positions of line centers in the HITRAN database by Δν = (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.

Lichens are not only a bioindicator of air pollution; they also affect the chemical composition of air. The qualitative composition of exometabolites in thalli of epiphytic lichens is studied using high-performance liquid chromatography. The comparative analysis of the fractional composition of deposited aerosol matter in water washouts of lichens shows it to be characterized by a bimodal particle distribution. It is postulated that the appearance of the fine fraction is associated with the generation of secondary organic aerosols on the surface of epiphytic lichens. Their precursors are the products of photoactivated reactions between deposited aerosol matter and highly volatile organic compounds which arrive on the lichen surface as a result of efflorescence. The mechanism of entry of secondary organic aerosols into the surface air layer under the radiometric photophoresis effect is discussed.

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 pretrained 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.

The results of hyperspectral sounding of the atmosphere at the Ural Atmospheric Station in Kourovka from 2012–2022 are presented. It is shown that the average rate of carbon dioxide growth in the atmosphere of this region is about 2.5 ppm per year. The amount of carbon dioxide absorbed from the atmosphere by the forest ecosystem per unit area during the growing season (April–September) in the vicinity of the carbon site in Kourovka is estimated using two independent methods. One method is based on the data on the CO₂ total column obtained from sounding the atmosphere with a ground-based high-resolution infrared Fourier spectrometer. The second method is based on the use of an artificial neural network with data from spectral channels of the MODIS satellite sensor as input. The results obtained by both methods have good agreement: the amount of CO₂ absorbed from the atmosphere by the forest ecosystem in the vicinity of the carbon site during the growing season of 2022 is ~1.5 t/ha according to the first method and ~1.3 t/ha according to the second method.

One of the possible sources of carbon dioxide emission into the atmosphere can be river ecosystems. The paper presents the results of measuring CO₂ fluxes from the surface of several rivers and lakes in Tomsk Region. In the experimental period, average carbon dioxide fluxes were 143.7 ± 21.7 (August 13–14, 2023), 53.3 ± 21.2 (August 19), and 80.4 ± 59.9 mgC m⁻² h⁻¹ for the Ob River; 66.1 ± 17.3 mgC m⁻² h⁻¹ for the Ket River; 33.3 ± 17.3 mgC m⁻² h⁻¹ for the swamp Karasevoye Lake, 50.2 ± 23.0 mgC m⁻² h⁻¹ for the Suiga River, and 81.9 ± 11.5 mgC m⁻² h⁻¹ for the Iksa River. The flux magnitudes significantly depended not only on the object of the study, but also on hydrometeorological conditions.

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 10 830 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 10 830-Å line.