Home – Home – Jornals – Atmospheric and Oceanic Optics 2023 number 10

Experimental and theoretical studies of optical non-line-of-sight communication in air and water media performed in Russia in 2012-2022 are rewieved. The main results of field, laboratory, and numerical experiments in the IR, visible, and UV wavelength ranges are given. In the laboratory experiments, a water-glycerine and atmospheric air mixture were used as a scattering medium. In the field experiments, communication was implemented in the near-surface air layer, as well as in artificial and natural water reservoirs (including through ice). Investigations were performed for coplanar and non-coplanar schemes of communication channels.

The absorption spectrum of ¹⁴N¹⁸O molecule in the 5200-5500 сm^-1 range was recorded for the first time using a Bruker IFS 125M Fourier spectrometer with a spectral resolution of 0.0056 сm^-1. The analysis of the spectrum made it possible to detect the vibrational-rotational lines of 3-0 band of the main transitions in X²Π electronic state of ¹⁴N¹⁸O molecule. For the main transitions ²Π_1/2 - ²Π_1/2 and ²Π_3/2 - ²Π_3/2, 102 line positions of Λ-doublet in three branches were registered. For 61 resolved doublets, the positions and relative intensities of each component of a doublet were determined. The maximum value of the rotational quantum number J was 29.5. The found experimental line positions in 3-0 band confirmed the calculated data given in HITRAN database. The frequencies of registered transitions, weighted in accordance with experimental uncertainties, have been processed, and the spectroscopic constants for the vibrational state v = 3 been determined. With the found spectroscopic constants, we predicted the rotational energy values up to J = 35.5 for the vibrational state v = 3 and, accordingly, the transition frequencies in 3-3 and 3-0 vibrational bands for ²Π_1/2 and ²Π_3/2 electronic states. The calculations performed showed agreement with the data given in HITRAN within the error specified in this database.

The transmission spectra of aerogel with nanopores filled with SO₂ and a mixture of H₂O and SO₂ are studied The measurements were carried out using a Bruker IFS 125 HR Fourier spectrometer in the spectral range 4500-10000 cm^-1 at a room temperature. It is found that the filling of nanopores of a sample with SO₂ and with a binary mixture of H₂O and SO₂ molecules affects the absorption bands of the aerogel. This change is reversible: when gases are pumped out, the transmission spectrum of the aerogel sample is restored.

Remote control of intense laser beams is an important problem of atmospheric optics. It is of special interest for atmospheric sounding, where turbulence can affect beam propagation. We experimentally study the effect of a turbulent layer produced at the beginning of a laser radiation propagation path on the characteristics of the filamentation domain and generation of high-intensity plasmaless channels for laser beams 2.5 and 5 cm diameter, including under the phase control of the transverse beam structure with a deformable mirror. Turbulence leads to the approach of the beginning of multifilamentation domain to the radiation source, which is, however, insignificant (< 10% of the path length). More important that a turbulent layer formed at the beginning of the path results in a multiple increase in the number of intense (mean intensity is ~ 10¹¹ - 10¹² W/cm²) light channels in a laser beam during its nonlinear propagation, which induce two-photon fluorescence of dyes at a distance of longer than 100 m from the radiation source with the signal level sufficient for its recording by the lidar scheme. Hence, this laser beam structure can be used for sounding natural and anthropogenic aerosols.

We calculate CH₄ radiative forcing from the analysis of outgoing thermal radiation (OTR) fluxes obtained by the MODTRAN radiative code for five climate atmospheric models and various methane concentrations (0.8, 1.8, and 2.5 ppm). OTR values decreased by ~ 0.15% compared to the pre-industrial era. Seasonal and spatial variations in OTR fluxes at current methane rates reach ~ 13%. To date, due to the increasing CH₄ concentration in the Earth’s atmosphere, methane RF is estimated at between -0.482 and -0.266 W/m².

Contribution of anthropogenic and wetland methane emissions in North Eurasia (> 40°N) and Russia into the near-surface CH₄ abundance at ZOTTO, Teriberka, and Tixi measurement sites is quantified using GEOS-chem global chemical-transport model. Numerical results agree well with the proposed semi-analytical solution, in which the total response in the CH₄ level at a given site is represented as the sum of direct (synoptic) and global terms. The annual average direct contribution of Russian anthropogenic emissions into CH₄ mixing ratio measured at ZOTTO (38.6 ppbv) is twice as large as that for Western Europe sources (17.7 ppbv). For the Arctic sites, the anthropogenic input from Russian and European anthropogenic sources is roughly similar (19.5 ppbv and 12.4 ppbv, correspondingly). The input from continental sources into methane abundance and its annual variability at the Arctic sites are generally lower compared to those at the ZOTTO site due to larger transport times from upstream CH₄ source regions. Atmospheric responses in methane levels at the Teriberca and Tixi sites to CH₄ continental sources are found to be very close, which is explained by spatial homogenization of the anthropogenic and biogenic signals in high latitudes.

To solve general and special problems of ground-based monitoring of the atmospheric electric field, it is necessary to identify global factors against the local variability of the monitoring data. The global unitary variation in the ionospheric potential, observed in the daily variation in the electric field, is distorted under the electrode effect near the earth's surface. The structure of the resulting electrode layer strongly depends on the degree of turbulent mixing, the specific conductivity of air, and the altitude of electric field measurement. Based on the equation for the total electric current, which follows from the theory of electrode effect of the surface air layer, we simulated daily variations in the electric field at different altitudes under different meteorological conditions. They revealed the dependence of the position and magnitude of the global extreme points of the electric field on the turbulent mixing coefficient, the electrical conductivity of air, and the electrode layer altitude. Our results can be useful for solving applied problems in geophysics, in particular, atmospheric electric field monitoring.

A technique for parallel registration of lidar signals in photon counting and charge accumulation modes at the Siberian lidar station of Institute of Atmospheric Optics, Siberian Branch, Russian Academy of Sciences (SLS) is described in detail. A device is designed and experimentally tested for recording lidar signals with the use of the combined technique at the unique SLS lidar. During the experimental testing of the device, the limits of applicability of the technique suggested to regular measurements of the vertical distribution of air temperature based on lidar signals of purely rotational Raman spectra are determined. The comparison between the lidar and satellite measurements shows their good agreement, which proves the high efficiency of the combined technique and confirms the capability of deriving the vertical distribution of atmospheric temperature throughout the altitude range of the primary mirror of the Raman lidar of SLS.

Based on the analysis of high-resolution FTIR spectra recorded at the atmospheric monitoring station of St. Petersburg State University during 2009-2022, a possibility of deriving NO₂ tropospheric column from ground-based measurements of direct solar radiation in the mid-IR range is studied. The best agreement (correlation coefficient r = 0.68) with simultaneous DOAS measurements of tropospheric NO₂ column at the same monitoring station is demonstrated by a retrieval strategy based on the use of the spectral range 2914.30-2914.85 cm^-1 in combination with Tikhonov-Phillips regularization. It is shown that FTIR measurements make it possible to detect high levels of tropospheric NO₂ at the SPbU monitoring station. Our results can be used at the FTIR stations of the NDACC network for significant expansion of the geography of tropospheric NO₂ monitoring.

This paper analyzes and generalizes the results of studies of turbulence in flame and in the vicinity of the combustion source during model steppe and crown fires in the period from 2019 to 2022 at the Base Experimental Complex of Institute of Atmospheric Optics SB RAS. The spectra of air temperature changes and the scales of induced atmospheric turbulence in the vicinity of the front of a model fire are obtained. For a steppe fire, the air temperature pulsation frequency ranges corresponding to the inertial and dissipative sections of the energy spectrum are found; dissipative processes begin to form at an altitude of 10 m at wave numbers with lgk > 1.58 and the corresponding pulsation frequency ƒ > 3 Hz; at an altitude of 3 m, dissipative processes are not observed. During a model crown fire, turbulent processes in the atmosphere correspond to the inertial part of the energy spectrum at an altitude of 10 m, and dissipative processes practically do not manifest themselves.

The results of measurement of underwater spectral irradiance at various depths in different types of intracontinental freshwater lakes, including the Kamginsky Bay of Lake Teletskoye, are presented. The measurements were carried out in summer and autumn 2018. The device for measuring the underwater spectral irradiance is described. Interference light filters with transmission maxima in different parts of the visible spectrum at wavelengths of 303, 361, 590, and 656 nm were used as light selective elements. An abnormally high absorption of light at a wavelength of 361 nm was detected in the pelagial of the Kamga Bay (territory of the Altai State Natural Biosphere Reserve), which is explained by the large amount of coniferous and deciduous wood rotting on the shores and flooded in the pelagial of the Bay and releasing phenolic compounds. The found dependence of the underwater spectral irradiance on depth is presented in the tabular form. It is shown that the underwater spectral irradiance significantly depends on the biomass of lake phytoplankton.