Atmospheric and Oceanic Optics最新文献

Transit observations of exoplanets make it possible to measure temperature and relative abundance of various elements in their atmospheres. The infrared line of metastable helium HeI 10 830 Å is widely used to study the atmospheres of exoplanets by the transit absorption method. The emission spectra of stars have a significant impact on the physical and chemical parameters of the upper layers of the atmospheres. In this paper, we consider the features of absorption in the helium line for stars of different spectral classes by numerical simulation. The results show the key role of the star’s emission spectrum in the formation of the upper atmosphere and in the amplitude of transit absorption of exoplanets in the HeI 10 830-Å line.

In continuation of the first part of the work, experimental results of Kelvin–Helmholtz wave sounding with a UV BSE-5 lidar (355 nm), with the sensitivity higher than that of BSE-4 lidar (532 nm), are presented. Experiments on atmospheric sounding with the BSE-5 lidar were carried out in the winter–spring period over a built-up area, which is a “heat island.” Improved lidar parameters in combination with thermal conditions in the atmospheric boundary layer, which is mainly stable stratified in the cold season, enables us to acquire new data on the shape of Kelvin–Helmholtz waves. Results of the analysis demonstrate that the sensitivity and potential of the BSE-5 lidar (355 nm) are higher than those of the BSE-4 lidar (532). It is ascertained that echo signals in both receiving channels of the lidar decrease by 30% after a sounding laser beam passes a turbulence intensity peak at the top of the wave arc. This effect of the turbulent atmosphere on echo signals of the lidar can be explained by beam broadening due to multiple scattering by random inhomogeneities of the medium.

The efficiency of laser radiation harmonic generation in nonlinear crystals is one of the most pressing problems in applied nonlinear optics. This work theoretically studies the second harmonic generation (SHG) in a converging (focused into a crystal) laser beam. The effect of the amplitude profile (AP) of fundamental laser radiation beam (before the lens) on the SHG efficiency and on optimal focusing and wave detuning parameters is estimated for the first time. It is ascertained that the optimal values of focusing and especially wave detuning parameters vary in very wide ranges depending on the AP. A strong influence of the AP on the effective aperture length, which mainly limits the SHG efficiency, is shown. Optimization of the AP enables increasing the SHG efficiency by no more than ∼10%.

Optical beam propagation through the atmosphere is suffering from turbulence condition and scattering due to the refractive index effects on propagation. In this paper, we study optical beam propagation under the UAE’s weather conditions. An outdoor test was carried out to gather the atmosphere parameters (temperature, wind, humidity, and refractive index) and feed them to a beam propagation model. The beam centroid was determined to study and predict the effects on it at different periods of the day.

Carbon dioxide absorption broadened by argon is studied on the basis of the asymptotic line wing theory. The line shape parameters concerned with the classical potential, which governs the center-of-mass motion, and the quantum intermolecular interaction potential are found. The temperature dependence of the CO₂–Ar absorption beyond the 4.3 μm band edge is explained through changes in the classical potential, which describes the temperature behavior of the second virial coefficient in the temperature region under study.

We estimate the long-term variability of the parameters of single-layer cloud fields over the territory of Western Siberia in winter for the period from 2001 to 2019 based on MODIS data. The main idea of the applied method is to use the results of recognition of 11 cloud types from daily winter (December, January, and February) daytime satellite images. Features of single-layer clouds are considered for three latitudinal zones of Western Siberia: southern (<60° N), transitional (60°–65° N), and northern (>65° N). We found linear trends for the following parameters of different cloud types: the coverage fraction of the target zones, optical thickness, effective particle radius, waterpath, and top height. The paper discusses the results of comparing the data we obtained with information from the annual Roshydromet assessment reports. We suggest hypotheses about the reasons for the anomalous parameter values in the time series for different cloud types in the latitudinal zones of Western Siberia under study in winter.

The problem of controlling the parameters of the filamentation region of high-power femtosecond laser pulses for amplitude modulation of radiation by a metal mesh mask is theoretically considered. In this case, the initial laser beam is split into individual lower energy subbeams. This leads to a pronounced regularization of the spatial structure of the filaments, which is formed at the stage of radiation self-focusing due to diffraction interaction between subbeams in a nonlinear medium. Using numerical simulation, it is found that the total length of the filamentation region of femtosecond laser radiation in air is reduced when using modulation meshes. At the same time, the longitudinal continuity of laser plasma in such filaments can significantly increase. It is shown that the spatial parameters of filaments (coordinate of the beginning, length, and continuity) can be controlled over a wide range by changing mesh parameters (crosshair thickness and cell size), as well as the position of the mesh mask relative to the laser beam center. The results are important for predicting the propagation of high-power femtosecond laser radiation in a nonlinear medium, in particular, along atmospheric paths.

Monitoring data on sulfates in atmospheric haze particles over Beijing in winter 2016 are considered. It is found that the source of sulfates in humidified haze particles is the catalytic oxidation of sulfur dioxide by molecular oxygen involving ions of transition metals ({text{(S}}{{{text{O}}}_{{{text{2}}{kern 1pt} {text{(gas)}}}}}xrightarrow{{{{{text{Mn}}} mathord{left/ {vphantom {{{text{Mn}}} {{text{Fe}}}}} right. kern-0em} {{text{Fe}}}}{text{,}}{{{text{O}}}_{{text{2}}}}}}{text{SO}}_{{4({text{aq}})}}^{{2 - }})) proceeding in a branched mode. Concentration conditions of this process and the features of its dynamics in the atmosphere are discussed. The agreement between the calculated content of ({text{SO}}_{{4({text{aq}})}}^{{2 - }}) in particles and monitoring data indicates that a branched mode of catalytic conversion of SO_{2 (gas)} in the atmosphere exists and represents a new source of sulfates. This fast nonphotochemical channel should be taken into account in inventory system of sulfate sources in the global atmosphere.

The possibilities of using molecular scattering to determine the wind speed from measurements with a pulsed coherent Doppler lidar (PCDL) from an aircraft at altitudes from 10 to 20 km are numerically studied. The simulation was carried out for sounding radiation at wavelengths of 1 and 2 μm focused at 500 m, the aperture diameter of the receiving-transmitting telescope was set equal to 10 cm. It is shown that the threshold SNR in measurements from an aircraft is attained at pulse energy much lower than when sounding from the Earth. Modern PCDLs with sounding pulse energies of 1–4 mJ, after adding a molecular scattering recording channel, can be used for airborne wind measurements at altitudes of 10–20 km.

Room temperature cavity ring-down spectra (CRDS) of hydrogen sulfide were recorded at three pressures of 10, 20, and 30 Torr in the 12 950–13 300 cm^–1 range with the sensitivity on the order of 3 × 10^–11 cm^–1 in terms of absorption coefficient. The analysis of these spectra was performed. The line positions and intensities were retrieved from these spectra. The theoretical simulation of these spectra was performed within the method of effective operators. The comparison of the measured line positions and intensities to the values obtained within variational calculation was done. The considerable difference was found between calculated (Azzam A.A.A., Yurchenko S.N., Tennyson J., Naumenko O.V. Exomol line lists XVI: A hot line list for H₂S // Mon. Not. R. Astron. Soc. 2016. V. 460. P. 4063–4074) and observed line positions and intensities.