Atmospheric and Oceanic Optics最新文献

Methane is one of key greenhouse gases, whose concentration has been increasing in recent decades, thus increasing the Earth’s surface temperature. To monitor the methane content in the atmosphere the accurate knowledge of the absorption spectrum of CH₄ molecule is required. In this work, the parameters of methane absorption lines broadened by atmospheric air pressure are presented in the spectral region 4345–4360 cm⁻¹. Data were derived from spectra recorded at a Bruker IFS 125HR Fourier spectrometer with a spectral resolution of 0.005–0.01 cm⁻¹ at room temperature and five values of buffer gas pressure. Atmospheric transmission was simulated using the derived results and line parameters from HITRAN and GEISA spectroscopic databases. The comparison with measured atmospheric solar spectra shows the CH₄ absorption line parameters found in this work to coincide the best in terms of root-mean-square deviation.

The response of forest ecosystems to changing climate conditions is studied by many researchers. In this work, the relationships between variations in the residual gas content in discs of coniferous and deciduous trees growing in and around Tomsk (southeast of Western Siberia) and the North Atlantic Oscillation (NAO) are analyzed. We have found (1) a significant correlation between the air temperature in Tomsk region and the NAO index; (2) coherent fluctuations in the chronologies of gas components of deciduous tree discs and in the air temperature during the growing season around a 4-year cycle; (3) the correlation coefficients of the NAO index with the chronologies of CO₂ (CO₂ + H₂O) and the ring width of the six (of eight) tree discs. A conclusion is drawn that the North Atlantic Oscillation can affect the life activity of some Siberian tree species (on a 4-year time scale). The results can be used in studies of biospheric and atmospheric processes with the aim of considering the effects of remote sources of air pressure variations on forest ecosystems.

Modern changes in the global climate are accompanied by rising air and soil temperatures. How do they affect soil respiration and should we expect a change in greenhouse gas emissions? These questions cannot be answered without studying the soil–air gas exchange. In this work, we analyze greenhouse gas fluxes at the soil–air interface measured at the Fonovaya Observatory in 2023 with the use of three chambers, transparent and opaque chambers on soil areas with vegetation and a transparent chamber on soil without vegetation. A stable CO₂ and CH₄ sink throughout the growing season is shown. For carbon dioxide, on the contrary, a weak positive flux was observed. A steady sink of N₂O from the atmosphere occurred from May to mid-August; its value attained −600 mg m⁻² h⁻¹ in June and July; the methane flux (sink) attained −0.08 mg m⁻² h⁻¹. The nitrous oxide flux fluctuated about zero with the daily average within ± 0.02 mg m⁻² h⁻¹. For CO₂, a nonlinear positive relationship between the increase in vegetation respiration and soil temperature is revealed. Linear temperature dependence is found for methane fluxes in all three chambers, that is, an increase in soil temperature enhances CH₄ absorption. N₂O fluxes show very weak positive dependence on the soil temperature in both transparent chambers (with and without vegetation). The estimates of the contribution of CO₂ fluxes from the soil show that microbial respiration can contribute from 46.7 to 77.9% to the total grassland ecosystem respiration during nighttime. The daily average share of methane absorption by soil due to diffusion and oxidation by methanotrophs not associated with plants varies from 5.3 to 48.3%; it becomes smaller during the daytime and increases at night. The contribution of soil without vegetation to the total N₂O flux can attain 92.3%. The results expand knowledge about the soil–air gas exchange under changing climate conditions.

The development of instruments for remote detection of clear-air turbulence (CAT) for early warning of aircraft crew about the danger is an urgent problem today. In this work, we describe the design and technical features of BSE-6 turbulent lidar mounted onboard an aircraft for experimental testing of CAT remote sensing technique. The quality of assembly and adjustment was verified in comparison between theoretical calculations and real echo signals. The system was tested for thermomechanical stability. The improvement of the turbulent lidar is to ensure early detection of CAT from an aircraft and remote control of the turbulence intensity in the atmospheric boundary layer from the ground, for example, along glide paths at airports.

Laser guide stars (LGS) technique is an integral part of modern adaptive optics systems of ground-based telescopes. The requirements for the energy, spectral, and spatiotemporal characteristics of a laser beam for creating a sodium LGS and for an adaptive optics system as a whole are largely related to the atmospheric parameters of a telescope site. A way of optimizing the brightness of a sodium LGS is the choice of laser linewidth. In this work, the effect of laser radiation linewidth (from 10 MHz to 3.5 GHz) on the magnitude of the return photon flux from a sodium LGS is estimated based on numerical simulation of the interaction of circularly polarized laser radiation with mesospheric sodium atoms in midlatitude atmosphere in the Russian Federation. The results can be used for the design of adaptive optics systems operating by the signals from a LGS.

The influence of deviations from the Kolmogorov–Obukhov model in the spectra of refractive index fluctuations in a supersonic air flow on transmitted optical radiation is studied. Statistical moments of a field are analytically estimated; laser radiation propagation through a high-speed air flow generated during flowing around an aircraft is simulated. The estimates of the coherence length and the relative dispersion of optical wave intensity fluctuations are compared. Consideration of deviations from the model of developed turbulence is shown to cause significant (several times) changes in the estimates of laser beam characteristics at a distance of several hundred meters. The results can be used to estimate radiation distortions under the turbulence effect in an optically active layer near the surface of supersonic aircraft on location and communication routes.

The influence of the morphology and composition of thin films which form the structure of dielectric mirrors of optical cavities of coherent sources for lidars is studied. TiO₂/SiO₂ and ZnS/YbF₃ dielectric mirrors were simulated in Optilayer software; their morphological features were determined with the use of electron and atomic force microscopy. Interference coating of the calculated structure was deposited onto a substrate by the ion-beam sputtering method. The Nd:YAG laser- (wavelength of 1064 nm) induced breakdown threshold was found to be 4 J/cm² for a TiO₂/SiO₂ mirror and 3.2 J/cm² for a ZnS/YbF₃ mirror. The result can be useful for manufacturing dielectric mirrors with high optical breakdown thresholds for both sources and detectors of lidar systems.

Saint Petersburg is the second most populous city in the Russian Federation and the fourth in Europe. According to official statistics, ∼5.6 million people permanently live in the city. In order to experimentally estimate greenhouse gas emissions from the territory of the St. Petersburg agglomeration, an original combined approach was developed and implemented during EMME-2019 and ЕММЕ-2020 observational campaigns. The paper summarizes the results of mobile experiments in 2019 and 2020. The period March – early May chosen for the EMME campaigns is shown to be optimal for estimating CO₂ emissions. The average anthropogenic additives caused by emissions from the territory of St. Petersburg were assessed at ∼1.07 ppmv for CO₂ and ∼6.61 ppbv for CH₄. Experimental estimates of specific greenhouse gas fluxes for the territory of the St. Petersburg agglomeration amounted to 72 kt km⁻² year⁻¹ CO₂ and 198 t km⁻² year⁻¹ CH₄ for six days of the campaign in 2020; 80 kt km⁻² year⁻¹ CO₂ and 161 t km⁻² year⁻¹ CH₄ for 15 days of the campaigns in 2019 and 2020. The CH₄/CO₂ and CO/CO₂ emission ratios for St. Petersburg in March–early May 2020 averaged 6.4 and 5.7 ppbv/ppmv, respectively. Lockdown restrictions due to COVID-19 pandemic affected the structure of emission from the territory of St. Petersburg, namely, a sharp decrease in transport activity significantly decreased CO emissions from motor vehicles.

Laser remote sensing of cirrus clouds is accompanied by the problem of taking into account the multiple scattering of radiation, which influences the reliability of measurement interpretation. The contribution of multiple scattering of radiation to echo signals of a spaceborne lidar is estimated. The nonstationary problem of laser pulse propagation in continuous cirrus clouds with separation by scattering multiplicities is solved by the Monte Carlo method at different values of the optical and microstructural characteristics of clouds (optical thickness and shape and size of ice particles) and lidar parameters (distance from the sensing object, beam divergence, and field of view of the receiver). Numerical experiments were carried out taking into account the permissible range of the parameters for operational or promising spaceborne lidar systems. The features of the formation of the backward signal when aerosol and Rayleigh particles, as well as the underlying cloud layer, are introduced into the atmospheric model are discussed. The simulation results indicate the high sensitivity of the echo signal part caused by multiply scattered radiation to the parameters under study, which should be taken into account when formulating and solving inverse problems.

The interest in aerosol studies in the Arctic stems from the large dynamics of the climate processes and active economical development of this region. The number of polar stations, available at present, is insufficient to determine the aerosol spatial distribution over the territory of the Arctic Ocean (AO). In this paper, the long-term studies in the Eurasian sector of the Arctic Ocean (AO) (19 ship-based expeditions in 2007–2023) are used to statistically generalize the volume concentrations of fine and coarse aerosol (V_f and V_с) in the near-water layer and the aerosol optical depth (AOD) of the atmosphere. The average AOD (0.5 μm) was 0.061 with an Ångström exponent of 0.9; the average concentrations of fine and coarse aerosol were 0.35 and 2.5 μm³/cm³, respectively. The content of fine aerosol was the largest in the atmosphere over the Norwegian and Barents Seas. The spatial distribution was characterized by the decline in the concentrations in northern and eastern directions: the average V_f value decreased by a factor of 1.7 (from 0.43 to 0.26 μm³/cm³) from the Barents to Chukchi Sea. In the spatial distribution of coarse aerosol very high concentrations were in the southwestern part of the Kara Sea; the average V_с was 4.18 μm³/cm³. The content of coarse aerosol were in the Kara Sea severalfold decreased in the eastern and western directions. These results can be used in planning the economical development of the Arctic region and refining climate models.