Atmospheric and Oceanic Optics最新文献

This paper presents the analysis and generalization of the results of studies of turbulence in flame and in the vicinity of a combustion source during model steppe and crown fires performed at the Basic Experimental Complex of Institute of Atmospheric Optics, Siberian Branch, Russian Academy of Sciences, in the period from 2019 to 2022. 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. The ranges of air temperature pulsation frequency corresponding to the inertial and dissipative sections of the energy spectrum are found for a steppe fire; dissipative processes start running at an altitude of 10 m at wavenumbers with log k > 1.58 and the corresponding pulsation frequency f > 3 Hz; no dissipative processes are observed at an altitude of 3 m. 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; dissipative processes hardly manifest themselves.

Results of numerical simulations of optical radiation focusing by a cluster of identical nanospheres close packed into a spherical volume (a “metaparticle”) are presented. Parameters of the focal region (intensity and longitudinal and transverse sizes) formed by metaparticles with different internal structure are calculated. It is shown that the problem of optical radiation focusing by a spherical cluster of nanoparticles can be reduced in certain cases to the problem of light focusing by a homogeneous spherical particle with an effective refractive index derived from the effective medium theory. Moreover, certain spherical cluster topologies make it possible to improve optical focusing in the near-field region, in particular, to increase the peak intensity or enhance its spatial localization.

Results of numerical simulation of the return flux from a sodium laser guide star for atmospheric conditions of astronomical observatories of the North Caucasus are presented. The simulation is performed in accordance with modern concepts of the physics of the interaction of polarized laser radiation with mesospheric sodium atoms. Two cases of producing an artificial reference source by laser radiation, with circular and linear polarizations, are considered. The limitations of the photon flux due to the saturation effect are estimated.

Characteristics of clouds which produced heavy precipitation in St. Petersburg and Leningrad oblast on June 18, 2020, are considered based on measurements with a C-band Doppler radar, Pluvio² 200 precipitation gauges, and a Blitzortung lightning detection system. To assess the intensity of precipitation, different values of the coefficients in the Marshall–Palmer Z–R relation are studied. We show that it is reasonable to use the specific differential phase to calculate the precipitation intensity when it exceeds 30 mm/h and precipitation consists of raindrops and hail. The top of the clouds exceeded 12 km, the maximal reflectivity was higher than 52 dBZ, and the maximal precipitation intensity could exceed 160 mm/h. A significant volume of a cloud was occupied by hail particles, which were recorded from the Earth’s surface up to an altitude of 10 km. The highest reflectance was recorded in the precipitation zone, as well as in the hydrometeors melting area. All the clouds under study were thunderstorms. A sufficiently high correlation between the frequency of lightning and the intensity of precipitation is noted: the Spearman’s correlation coefficient exceeds 0.7.

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 4500–10 000 cm⁻¹ at 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.

The absorption spectrum of ¹⁴N¹⁸O molecule in the 5200–5500 сm⁻¹ region 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 the 3–0 band of the main transitions in the X²Π electronic state of the ¹⁴N¹⁸O molecule. For the main ²Π_1/2–²Π_1/2 and ²Π_3/2–²Π_3/2 transitions, positions of 102 lines from a Λ-doublet were recorded in three branches. The positions and relative intensities of each component of the doublet were determined for 61 resolved doublets. The maximal rotational quantum number J was 29.5. The experimental line positions in the 3–0 band confirm the calculated data presented in HITRAN database. The frequencies of recorded transitions, weighted in accordance with experimental uncertainties, were processed, and the spectroscopic constants were determined for the vibrational state ({v}) = 3. With the found spectroscopic constants, we predicted the rotational energy values up to J = 35.5 for the vibrational state ({v}) = 3 and transition frequencies in the 3–3 and 3–0 vibrational bands for the ²Π_1/2 and ²Π_3/2 electronic states. The calculation results agree with the data given in HITRAN within the error specified in this database.

The validation of H₂O absorption lines parameters in the modern spectroscopic databases such as HITRAN2016, HITRAN2020, GEISA2020, and W2020 is carried out in the visible region 16 700–17 000 cm⁻¹. The H₂O transmission spectra are simulated with the spectroscopic databases and compared with laboratory spectra of pure water vapor and H₂O–N₂ mixture (P = 1 atm) recorded using a Fourier spectrometer with light-emitting diodes of high luminance. The parameters of 65 H₂O absorption lines from HITRAN2020 database are corrected on the basis of the measurements. The positions of 32 lines, intensities of 51 lines, and self-broadening coefficients of 10 lines are improved. The ratio of the HITRAN2020 broadening coefficients to the experimental values is close to 1, whereas the air pressure-induced line shift coefficients in the spectroscopic databases are, on average, two times higher than the experimental values, and therefore, our previously obtained experimental values of N₂ pressure-induced line shift coefficients are used to simulate the transmission spectra of the H₂O–N₂ mixture. The difference of the experimental spectra from the spectra calculated with HITRAN2016, HITRAN2020, GEISA2020, W2020, and corrected HITRAN2020cor is estimated by the root-mean-square deviations RMS = 1.49 × 10^–4, 1.64 × 10^–4, 3.96 × 10^–4, 3.49 × 10^–4, and 1.26 × 10^–4, respectively, in the case of pure water vapor and 1.15 × 10^–4, 1.1 × 10^–4, 2.23 × 10^–4, 2.28 × 10^–4, and 0.86 × 10^–4 in the case of H₂O–N₂ mixture.

Monitoring measurements of aerosol characteristics and meteorological parameters in the lower atmospheric layer in the winter periods of 2016–2022 in Akademgorodok located in the southeast of Tomsk were used to analyze the conditions for the occurrence of extreme concentrations of submicron particles and black carbon in their composition in the surface layer. It is shown that when surface air temperature inversion and weak (down to 1.5 m/s) wind (air stagnation) occur in combination, the average aerosol characteristics under study increase by as much as a factor of three, and by as much as a factor of 7–8 relative to the seasonal averages in the case of a weak northwesterly wind. It is found that in situations with multiday air stagnation, the typical daily behavior, characterized by the afternoon minimum, changes. The concentrations increase until 15:00 LT up to the values 1.8 times larger than the nighttime minimum. On the other winter days, the maximum occurs at 10:00 LT, with the concentrations of submicron (black carbon) particles being a factor of 1.2 (a factor of 1.5) larger than the nighttime minimum.

The radiative forcing due to methane is estimated from the analysis of upwelling thermal radiation (UTR) fluxes calculated with the use of MODTRAN radiative code for five climate atmospheric models and three methane content values: preindustrial (0.8 ppm), current (1.8 ppm), and future (2.5 ppm). The current values of UTR flux are ∼0.15% lower as compared to the preindustrial era. Seasonal and spatial variations in UTR fluxes attain ∼13% at the current methane content. The radiative forcing due to the growth of atmospheric methane since the preindustrial era is estimated at −0.482 to −0.266 W/m².

Experimental and theoretical studies performed in Russia in 2012–2022 on non-line-of-sight optical communication in air and water media are reviewed. 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-glycerin and atmospheric air mixture was used as scattering media. In the field experiments, optical communication was implemented in the near-surface air layer, as well as in artificial and natural water reservoirs (including through ice in winter). The investigations were performed for coplanar and noncoplanar schemes of communication channels.