Home – Home – Jornals – Atmospheric and Oceanic Optics 2019 number 5

Based on the numerical simulation and qualitative analysis, the effect of the group velocity dispersion on the formation of light structures during self-focusing and filamentation of femtosecond titanium-sapphire laser pulses in air was studied. It was found that dispersion occurs when the dispersion length is not the smallest process scale. Based on the results of numerical solutions of the nonlinear Schrödinger equation in a Kerr-plasma dissipative dispersion medium using the method of diffraction-beam tubes, the main regularities of filamentation of femtosecond laser pulses in air at various pulse durations, initial beam radii, and peak emission powers were determined. It was shown that the relative (normalized to Rayleigh length) coordinate of the beginning of filamentation increases with increasing the dispersion distortion of the pulse. The length of the filamentation channel is reduced. For shorter laser pulses (tens of femtoseconds) the filamentation failure is observed, when the laser beam radius is increased. For this class of pulses, an increase in the size of the energy replenishing diffraction-beam tube occurs, and the angular divergence of the post-filamentation light channels also increases.

Critical evaluation of the available experimental data on the frequencies of the rotational and vibrational-rotational transitions of the OH molecule in the ground electronic state Х²Π is performed using the Ritz combination principle. The transition frequencies weighted in accordance with the experimental errors have been processed by the RITZ program code. The analysis of the dimensionless weighted deviations made it possible to exclude "bad frequencies" from consideration and to carry out processing with a standard deviation of 1.8. As a result of critical evaluation, a set of 1056 empirical RITZ energy levels is obtained with an appropriate uncertainty for each level. The empirical Ritz energy levels are compared with the calculated levels given in the HITRAN spectroscopic database.

The broadening and shift coefficients of H₂O absorption lines are compared for Ar, He, H₂, and N₂ buffer gases. The broadening and shift coefficients were derived from the analysis of the absorption spectra recorded with a Fourier spectrometer in the spectral range 8650-9020 cm^-1 with a spectral resolution of 0.01 cm^-1. Using two models of line profiles (Voigt and speed-dependent Voigt profiles) the parameters of the H₂O absorption lines were calculated. It is shown that the speed-dependent Voigt profile provides better agreement with experimental data.

The wind speed and atmospheric turbulence in the airport runway were measured using a passive optical method based on the correlation analysis of turbulent distortions of distant objects of observation. The optical path was organized in the area of the ground section of the plane descent glidepath near the start of the runway. After the aircraft passed above the line of sight of the meter, significant velocity emissions and increased turbulence, caused by the wake, against the background of a moderate side wind were stably recorded. The results indicate the practical applicability of this method for instrumental indication of the presence or absence of wake vortex tracks over the airport. This information can be useful in assessing the safe intervals in the process of organizing departure and landings of aircraft.

The results of a numerical analysis of the manifestation of the backscatter amplification effect in the regime of weak optical turbulence in dependence on diffractive size of the transmitting aperture are presented. It is shown that the magnitude and localization of the amplification of the mean power of the radiation back scattered in a turbulent atmosphere depends on the Fresnel number of the transmitting aperture. Since the Fresnel number changes with changes in the distance from which the lidar signal arrives, this must be taken into account when profiling the intensity of optical turbulence from the lidar data on the amplification of the mean power of scattered radiation.

The work presents the algorithm for determining cloud phase using the MSU-MR daily measurements on-board the Russian meteorological satellite Meteor-M N 2. The physical principles of the determination of cloud phase by using the reflectance at wavelengths of 1.6 and 3.7 mm and brightness temperatures at 11 and 12 mm are considered. The results of determining cloud phase with the algorithm presented are compared with the results of the algorithms developed for other satellite radiometers. The accuracy of the comparison is over 80%. The greatest inaccuracies are observed for thin semitransparent clouds because to additional radiation coming from the underlying surface, as well as for mixed clouds due to the specificity of the algorithm presented.

The numerical solution within the geometrical optics approximation of the light scattering matrices for ice crystals with arbitrary shape taking the absorption into account were presented. The results show that the absorption decreases the intensity of scattered light when a wavelength goes far to the IR. It was shown that the influence of absorption is less than basis points for 0.355 and 0.532 mm wavelengths, and less than several percent for 1.064 mm. For the near IR the influence of that effect could be more than several dozen percent.

The 14-channel RPG-HATPRO microwave radiometer has been operating at the Faculty of Physics, St. Petersburg State University since 2012. It performs continuous measurements of the cloud liquid water path (LWP). Along with the multiple quadratic regression (MQR) method provided by the instrument manufacturer, the “physical” retrieval algorithm, which is based on the inversion of the radiative transfer equation (IRTE), and the multiple linear regression (MLR) method are used. The estimates of the LWP retrieval errors are presented for the cases when MLR coefficients are derived from model calculations and from the experimental data (in the latter case, the IRTE results are used as reference data). It is shown that the application of the experimental data and the utilization of measurements in 7 spectral channels of the radiometer provide the LWP random error of 0.015-0.017 kg/m² which is two times lower than in case of derivation of regression coefficients from model calculations. The bias does not exceed 0.005 kg/m² in this case. It is demonstrated that the MLR results provide a reliable identification of clear-sky conditions if the criterion of minimal LWP variations is applied.

The dependence of variations in the surface ozone concentration on the absolute air humidity is studied based on measurements at the TOR station in 1994-2017. The analysis performed revealed a neutral dependence at positive temperatures and unexpectedly strong and alternating sign variability at negative temperatures. The absolute air humidity negatively affects the ozone formation in the surface air layer, decreasing the ozone concentration at temperatures of 0…-30 °C. At very low temperatures (lower -30 °C) the effect becomes positive, i.e., the ozone concentration on increases with the absolute air humidity.

A statistical analysis of the ground concentration of sulfur dioxide (SO₂) was carried out based on the measuring network of observations data in the cities of Kazakhstan. The highest concentrations are observed in large industrial cities. In large cities, the range of changes in sulfur dioxide concentrations from 0.01 to 0.09 mg/m³. In Ust-Kamenogorsk the content of dioxide varies in the range from 0.058 to 0.259 mg/m³ with a downward trend. Sulfur dioxide content analysis in the atmospheric column over the territory of Kazakhstan using reanalysis system MERRA 2. The annual sulfur dioxide average content vary from one of 2.43 to 2.73 mg/m², in 2010 this value reached to 3.16 mg/m². There is a SO₂ content decrease tendency in the atmospheric column in Kazakhstan. The total sulfur dioxide content in the atmospheric column decreased by 38% during the period from 1980 to 2018.

In 2017, at the Large Solar Vacuum Telescope of the Institute of Solar-Terrestrial Physics of SB RAS, an element base was created for developing methods for recording and correcting distortions of optical radiation passed through a layer of turbulent atmosphere; a three-stage image correction system was installed; software was developed, which provides, the statistical analysis of the quality of the formed image in BSWT and combines the work of a wavefront sensor, an image quality analyzer, and an astronomical instrument - a filter-recorder.

Laboratory simulation of the conditions for the blue “jet” beginning in the Earth’s atmosphere has been carried out. For this purpose, the diffuse “jet” formation and plasma buildup in corona and apokampic discharges on air has been studied. It is shown that “jet” is formed due to streamer breakdown, and their color depends on pressure. At atmospheric air pressures of 30-120 Torr, streamers starting from different parts of a repetitively pulsed discharge are recorded in a non-uniform electric field. It has been established that, before the breakdown, between the pointed electrodes, a corona discharge of a spherical shape is formed near a metal high-voltage electrode of positive polarity, from which streamer coronas start with increasing voltage. Data on the dimensions of the streamer head and the streamer propagation speeds in the corona and apokampic discharges are presented.