Vol 32, No 5 (2019)

Based on 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 Ti:sapphire laser pulses in air is studied. The main features of the filamentation have been determined at various pulse duration, initial beam radii, and peak radiation powers based on the results of numerical solutions of the nonlinear Schrödinger equation in a Kerr-plasma dissipative dispersion medium and using the diffraction-beam tube approach. Dispersion is detected in the cases where the dispersion length is not a minimum at the scale of the process. It is shown that the relative (normalized to Rayleigh length) coordinate of the beginning of filamentation increases as the dispersion distortions of the pulse increase, and the filamentation channel length is reduced. For shorter laser pulses (tens of femtoseconds), the filamentation ceases as the laser beam radius increases. The size of the energy-replenishing diffraction-beam tube and the angular divergence of postfilamentation light channels increase for this class of pulses.

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 an FTIR spectrometer in the spectral region 8650–9020 cm⁻¹ with a spectral resolution of 0.01 cm^–1. Using two model 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.

Wind speed and atmospheric turbulence near an airport runway were measured using a passive optical method, which is based on the correlation analysis of turbulent distortions of distant objects under observation. An optical path was set up in the region of the ground section of a descent glidepath near the beginning of the runway. After an aircraft passed above the line of sight of the measuring device, significant wind speed spikes and increased turbulence in the aircraft wake were detected against the background of a moderate crosswind. The results confirm the practical applicability of this method for instrumental detection of the presence or absence of vortex wakes over an airfield. This information can be useful in the assessment of the safe intervals in air traffic flow-management.

We discuss the results of measurements in the region of Cape Baranov (the Severnaya Zemlya archipelago) of the set of physicochemical characteristics of atmospheric aerosol: aerosol optical depth, aerosol and black carbon concentrations, elemental and ion compositions of aerosol, organic and elemental carbon contents in aerosol, as well as the isotopic composition of carbon in the aerosol and snow samples. It is shown that the average values of most aerosol characteristics, measured in April–June 2018, are a little lower than in the Arctic settlement Barentsburg (Spitsbergen archipelago) and several-fold smaller than in the south of Western Siberia in the same period.

A theoretical approach to calculation of the parameters of fractal-like aggregates based on gas-kinetic results for homogeneous spheres is presented. The essence of the approach consists in the replacement of a real fractal aggregate by a sphere equivalent in mobility and approximation of the aggregate density and thermal conductivity by their effective values. The effectiveness of the approach has been confirmed in comparison with known experimental data. It has two important restrictions: a fractal aggregate should consist of a great number of primary particles (100 and more), and primary particles should be monodisperse. Violation of these conditions leads to considerable divergence between theoretical and experimental results.

The measurements of soot aerosol concentration in Moscow and Beijing in 2004–2010 are presented. The variability ranges of one-time soot concentrations in this period of time had been 0.1–77 μg/m³ in Beijing and 0.1–22 μg/m³ in Moscow. The seven-year average daytime soot concentration in Beijing is 2.5 times higher than in Moscow. The seasonal behavior of the soot concentration is more pronounced in Moscow: the soot concentration is 33% lower in summer than in winter, and only 13% lower in Beijing. Analysis of back trajectories of air mass transport and variations in soot concentration showed that the soot content in the atmosphere of Beijing significantly increases when air masses are transported from industrially developed regions south of Beijing. The air pollution by soot in Moscow predominantly decreases due to advection when air masses from northern regions come to Moscow.

We studied the variations in time series of the near-surface water vapor partial pressure on the territory of Europe over a multiyear period. It is found that the contribution of fluctuations on time scales from 2 to 5 years is from 35 to 60% of the variance of the interannual variations. The spatial dependences of the local coherence between harmonics on 2–4 scales of Niño3.4 index and the water partial pressure in Europe are determined. We determined that the correlation of these variations reaches 0.7–0.9. It is shown that westward-propagating planetary waves play a significant role in energy transfer from equatorial regions to midlatitudes. This energy begins to increase in the winter of an El Niño year and reaches the maximum a year later.

The technique of the maximum of the function of accumulated spectra (MFAS) is used for the first time for estimating the wind velocity vector from measurements with a micropulsed coherent Doppler lidar (MPCDL) in the process of conical scanning by a probing beam. It is established in the experiment with the Windcube 200s MPCDL that MFAS technique makes it possible to increase the maximum altitude of retrieval of the vertical profiles of the wind speed and direction by 30% on average as compared to the filtered sine wave fitting.

Estimates of the error in determining the cloud liquid water path by the multiple linear regression (MLR) technique using different regression relations obtained both by model calculations and by experimental data (for reference, results of the method based on the inversion of the radiative transfer equation were taken) are presented. It is shown that if the MLR method is trained by experimental data and measurements in seven spectral channels of the radiometer, the random component of the liquid water path error in the cloud is 0.015–0.017 kg/m², which is half that obtained when trained by the results of model calculations. The cloud liquid water path bias does not exceed 0.005 kg/m². The MLR results allow one to reliably identify periods of clear sky by the criterion of the minimum variance of the water content.

A two-component energy-balance climate model (EBM) is considered, which allows estimating the transient response of the global mean surface temperature (i.e., the Earth climate system response) to radiative forcing due to atmospheric aerosols and radiatively active gases in accordance with the specified scenarios of their atmospheric content. An expression for the impulse response function of EBM is analytically derived. The response of the climate system to arbitrary external radiative forcing is calculated as a convolution of two functions – an impulse response function and a function describing the radiative forcing. The comparative analysis of the numerical calculation results for two idealized scenarios of radiative forcing (step function and linearly increasing radiative disturbance) and the exact solution analytically derived shows a fairly high accuracy of the approach. Using the impulse response function, we estimate the response of the global mean surface temperature to radiative forcing specified by several scenarios of an increase in the concentrations of greenhouse gases (four RCP scenarios) and volcanic aerosol (1991 eruption of the Pinatubo volcano). Since the technique suggested for estimating the transient climate response to radiative forcing is quite accurate and computationally inexpensive, it can be used as an express analysis tool for estimating the climate system response to arbitrary radiative disturbance caused by natural and anthropogenic aerosols and radiatively active gases including greenhouse gases.

We describe a mathematical model developed for the adaptive control system of the composite primary mirror of a telescope similar in characteristics to the international project of the Millimetron space telescope. Results of numerical simulation of the adaptive control system with allowance for restrictions of the hardware–software implementation are presented. According to results of the simulation, the error of maintaining the shape of the composite primary mirror is estimated. The estimate corroborates the applicability of the mathematical model.

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