Home – Home – Jornals – Atmospheric and Oceanic Optics 2021 number 8

The dependence of limit of detection of Mg, Mn, Sr, Pb, Al, and B in aqueous solutions by femtosecond laser induced breakdown spectroscopy on the laser pulse repetition rate is studied. It is shown that at pulse repetition rates from 50 to 1000 Hz and under the same other experimental conditions, the best limits of detection for all elements are achieved at a laser pulse repetition rate of 166 Hz.

The results of comparative studies of the ratio of aerosol fractions in the surface air and snow layers chronologically linked to stratigraphically significant snowfalls are presented. Probable paths of winter air masses were reconstructed using backward trajectories calculated with NOAA HYSPLIT_4 model and gridded meteorology NCEP/NCAR Reanalysis. It is shown that the features of the formation of the winter aerosol field within the Ob-Tomsk interfluve are mainly associated with winds with a southern component.

The paper presents the results of the study of the Umov effect for large compare to the wavelength of the incident radiation nonspherical particles. The calculation was carried out for particles with maximal sizes of 100, 140, 170 and 200 microns. The results were obtained for 210 different refractive indices, the real part of which varied from 1.3 to 1.6 with a step of 0.5, the imaginary part varied from 0 to 0.1344. It has been shown that the Umov effect is fulfilled for all the particles when the imaginary part of the refractive index is less than 0.001.

The role of heat fluxes in phytoplankton production during the summer heating of Barguzin Bay of Lake Baikal was explored using mathematical modeling. The results of numerical experiments showed effects of longwave radiation and latent and sensible heat fluxes on phytoplankton growth in the upper layers. This study found that the largest concentrations of phytoplankton biomass are localized at some distance from the mouth of the Barguzin River.

The optical scheme and technical characteristics are described of an experimental setup for atmospheric studies of a possibility of compensating for aberrations of the initial wavefront of an optical beam by the aperture sensing technique based on the signal of atmospheric backscatter of radiation from an additional laser source.

The results are presented of experimental studies of a possibility of compensating aberrations of the initial wavefront of an optical beam by the aperture based on the atmospheric backscatter signal of radiation from an additional laser source at a different wavelength. It is shown that the makes it possible to reduce the beam wavefront aberrations by several times, down to 1-2 wavelengths at optimal angles of view of the scattered radiation receiver. As a result, the distortions of the intensity distribution in a beam cross section and beam divergence decrease and the power in the beam paraxial region increases.

The pressure jump method was used to determine the energy release in an apokampic discharge at various air pressures. The maximum energy release and electroluminescence in the NUV spectral range are achieved in the pressure range from 85 to 92 Torr, which roughly corresponds to the formation heights of such optical phenomena in the middle atmosphere as blue jets, starters, and giant jets. The facts found make it possible to supplement the picture of the formation of these phenomena.

An algorithm for estimating sizes of regions affected by cloudiness on the errors of retrieval the reflection coefficients of the Earth’s surface areas observed through gaps in a cloudy field is suggested. The algorithm is based on statistical simulation by the Monte-Carlo method of the process of radiation transfer through broken stochastic cloudiness. Two stochastic models of cloudy fields are considered: 1) clouds shaped as parallelepipeds and 2) clouds shaped as paraboloids. The method is tested for two fragments of actual MODIS images. It is shown that the broken cloudiness influences the error in the reflection coefficient retrieved at distances from 5-7 to 25 km from the observation point (depending on the observation conditions).

The paper presents estimates of recent numerical visibility forecast methods in the atmosphere. METAR reports for 786 airports in Europe and central Russia for the period 01.02.2020-01.08.2020 were used as visibility standards. The estimates were summarized in three ranges: poor visibility (0-1500 m), satisfactory (1500-3000), and good (3000 or more) for certain regions of Western Europe and the European territory of Russia. It is shown that the forecast of poor visibility by all the considered methods for up to 36-48 hours can be satisfactory. For a longer period, the accuracy drops noticeably, and the forecast using the method presented by the authors shows high accuracy for low visibility in most regions. The rest of the methods make it possible to predict good visibility.

A method for estimating cross sections of excitation transfer in collisions with atoms of rare-earth metals (REM) is presented. The cases of excitation transfer in collisions of REM atoms in unscreened resonant states 6 s 6 p with REM atoms in the ground state, as well as REM atoms in screened resonant states 5 d 6 s ² with inert gas atoms are considered. The determination of the cross sections is based on the fact of collisional population of the upper laser levels from close-lying resonant levels excited by electron impact in REM vapor lasers. The quantities required for calculating the cross sections are determined from the active laser medium parameters and average lasing power. The advantages and disadvantages of the method suggested in comparison with methods based on optical excitation of metal atoms and recording non-resonant fluorescence are discussed.

The values of 13 partial and 15 effective cross sections of excitation transfer in Dy-Dy, Tm-Er, Tm-Tm, and Tm-He collisions are estimated. The active media of Dy, Tm, and Er-Tm vapor lasers with buffer gas He were used as collisional ones. The determination of the cross sections is based on the fact of collisional population of the upper laser levels from close-lying resonant levels excited by electron impact in discharge. The quantities required for calculating the cross sections were determined from the laser medium parameters. The partial cross sections of collisional excitation transfer, depending on the excitation cross sections of resonant levels, type of collisions and energy defect between resonant and upper laser levels are ~10^-16-10^-14 cm², whereas the effective cross sections are ~ 10^-18 - 10^-15 cm².