Home – Home – Jornals – Atmospheric and Oceanic Optics 2023 number 8

The H₂O absorption lines broadened by the air pressure were recorded using IFS 125HR Fourier spectrometer in the spectral region 3000-7500 cm^-1. The H₂O absorption line intensities are determined for the modified Voigt profile which takes into account the dependence of the broadening on the speed of colliding molecules. The comparison with literature data is carried out. The intensities of the H₂O absorption lines obtained in this work can serve both as a basis for improving the calculations of absorption lines and for various atmospheric applications that require the high precision intensity values.

The results of experiments on the propagation of vortex optical beams in an artificial convective turbulent medium along a path 12 m long are presented. An artificial turbulent medium is created at a laboratory bench, where laser beams are generated with different values of the topological charge of the orbital angular momentum of the vortex optical field. The characteristics of the path and the parameters of the propagating radiation in the experiment correspond to the propagation conditions, which can be described in terms of geometric optics. It has been established that during the propagation of an optical beam, in the near diffraction zone, as the optical turbulence increases, the instantaneous distributions of the intensity of vortex beams become speckled, the original ring structure of the beam is distorted and disappears. In the averaged intensity distributions, the ring structure is gradually blurring with strengthening the refractive turbulence and becomes close to that of a Gaussian beam with the intensity maximum at the center. The random wandering of vortex beams, whose initial transverse size increases with the topological charge, and beams, whose initial transverse size remains unchanged with a change of the topological charge, is compared. It is shown that the amplitude of random displacements of a vortex beam energy centroid is independent of the topological charge.

In the present work, we have studied the potentials of an additional Raman channel in the IR region of spectrum for the determination of the aerosol microphysical parameters. A procedure is suggested for simultaneous retrieving the characteristics of a spherical particle, the complex refractivity index m = m_real + i × m_image and the bimodal size distribution function U ( r ), using laser sensing data. A possibility of a separate fraction-wise estimation of m + U ( r ) is studied for weakly absorbing particles for m_image ≤ 0.010, when m^fine ≠ m^coarse. The algorithms are tested for one m^fine = 1.50 + i × 0.01 and nine m^coarse( m_real = 1.40, 1.50, and 1.60, m_image = 0.0001 and 0; m_real = 1.40, 1.50, and 1.60; m_image = 0.0001, 0.001, and 0.01). In order to take into account the influence of the contribution from the modal particles into the total concentration, 462 empirical models of U ( r ) are used.

The work considers the distribution of tropospheric ozone in Russia in 2022 according to 33 stations located in different physical and geographical zones, as well as its vertical distribution according to the results of aircraft sensing. It was shown that ozone concentration stations the maximum permissible daily average concentrations established by the domestic hygienic standard at all exceed. In some regions, the maximum permissible concentrations of the working zone and the maximum one-time hourly average concentrations are exceeded. The current situation causes the need to widely inform the population about the monitoring results and develop environmental measures to reduce the level of ozone concentration in the surface air layer.

The results of experiments in the Large Aerosol Chamber of RPA Typhoon revealed the appearance of new aerosol particles larger than 15 nm in an aerosol-free volume of atmospheric air isolated from the external environment in darkness 20 min after the air purification. The generation of new particles is associated with the possible presence of gases - precursors in the atmospheric air. The gases-precursors turn into aerosols under the action of cosmic rays penetrating into the chamber. The experimentally derived particle size spectrum evolution (over several days) shows that the generation of new aerosol particles lasts no more than 20 hours. During the evolution, the particles become larger and reach more than 100 nm size. After repeated purification of the air inside the chamber with the removal of newly generated aerosols, no new particles were detected for 10 days.

Characteristics of clouds which produced heavy precipitation in St. Petersburg and Leningrad region on June 18, 2020 are considered based on measurements with C-band Doppler radar, Pluvio² 200 weight precipitation gauges, and Blitzortung lightning detection system. To assess the intensity of precipitation, different values of the coefficients in the Marshall-Palmer Z - R ratio are studied. We show that it is reasonable to use the specific differential phase to calculate the precipitation intensity when it exceeds 30 mm/hour and precipitation consists of raindrops and hail. The top of the clouds exceeded 12 km, the maximal reflectivity was higher than 52 dBZ, the maximal precipitation intensity could exceed 160 mm/hr. 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 thunderstorm. A sufficiently high correlation between the frequency of lightning and the intensity of precipitation is noted. Spearman's correlation coefficient exceeds 0.7.

An algorithm for retrieval of cloud-base height (CBH) from passive remote sensing data based on artificial intelligence methods is presented. Determining the CBH is considered as a special case of the classification problem. The algorithm is trained by comparing the results of active measurements of the CBH for single-layer clouds by the ground-based ceilometers (ASOS network), CALIOP lidar (CALIPSO satellite), and CPR radar (CloudSat satellite) with the cloud parameters obtained from the MODIS spectroradiometer (Aqua satellite). The results of estimating the capabilities of active tools to determine the CBH depending on optical thickness of clouds are presented. The CBH retrieval algorithm is based on the use of three independent Kohonen neural networks trained on the data of the above devices. The results of determining the CBH for single-layer clouds by the developed classifier based on daytime MODIS images of the territory of Western Siberia obtained in summer are discussed. It is established that the algorithm generally underestimates the CBH. The average bias of the resulting scores from the ASOS/CALIOP/CPR reference data is -0.2 km at a standard deviation of 1.2 km.

A simplified mathematical model and the results of experimental studies on the spectral composition of radiation from a compact waveguide CO₂ laser with RF excitation for a laser opto-acoustic gas analyzer are presented. The aim is to improve measurement accuracy by eliminating unwanted 10 R -branch lines from the laser spectrum. Laser radiation signatures are measured under various resonator and active medium parameters without the use of additional selection elements. It is demonstrated that optimal signatures can be achieved by selecting the appropriate pressure of the gas mixture, the transmittance coefficient of the output mirror, and the optimal resonator length, which can be obtained by varying the nominal (base) length within a range of 2 mm. The effectiveness of optimizing the spectral composition of laser radiation is practically confirmed by statistical results for 64 lasers. The open up new possibilities for improving the measurement accuracy of SF₆ laser opto-acoustic gas analyzers and extending its application in various fields of science and technology.

The results of the modernization of the mobile aerosol Raman lidar "LOZA-A2" are presented. Along with measurements of the vibrational component of spontaneous Raman scattering of lidar signals simultaneous measurements of signals of purely rotational Raman scattering are carried out. The technique for interpreting Raman lidar sensing data is considered. The data of simultaneous measurements of the vibrational-rotational and purely rotational components of the Raman scattering during sounding of the atmosphere above Lake Baikal are obtained. The results of retrieving the vertical profiles of the optical characteristics of the atmosphere at a wavelength 532 nm from these data are presented.

The spatial distribution of the average air density in a supersonic jet is analyzed based on the results of laser transillumination. The algorithm for retrieving the average density from deviations of the translucent wave front transverse with respect to the jet axis was tested in experiments at the Vertical Jet Setup of ITAM SB RAS. The retrieval results are compared with the data of contact measurements known from the literature and with the results of numerical simulation. A good sensitivity of local wavefront slopes to fluctuations in air density at frequencies of discrete acoustic tones is show, which opens up possibilities for experimental study of their spatial structure inside the jet channel.