Vol 30, No 3 (2017)

Results of laboratory and numerical experiments on the multiple filamentation of high-power pulse Ti:Sapphire laser radiation (740 nm) in air are presented. The postfilamentation stage of pulse propagation in the form of intensive spatially localized light structures is investigated. The angular divergence of postfilamentation channels is studied under variation in the initial laser beam focusing. The threshold distance for the refilamentation of postfilamentation channels in a glass plate is measured.

Lidar polarization measurements of stratospheric aerosol were performed over Obninsk in 2012–2015. In all, over 300 altitude profiles of the aerosol backscattering coefficient at a wavelength of 532 nm in the altitude interval from 10 to 40 km were obtained. Overall, the measured aerosol backscattering characteristics are close to the known background values. During spring 2013, an elevated content of spherical-type aerosol was noted in the tropopause region, seemingly associated with sedimentation of aerosol structures formed during the fall of the Chelyabinsk meteorite. In July 2014 and 2015, layers of increased aerosol scattering were observed in the altitude interval from 10 to 15 km, associated with transcontinental transport of aerosol from Canadian forest fires. Integrated backscattering and extinction characteristics are estimated for the lower (from tropopause level to 15 km) and middle (from 15 to 30 km) stratospheric layers. It is found that the contribution of the lower layer to these optical characteristics is 1.8 and 1.6 times larger than the contribution of the middle layer.

Results of the analysis of the “instantaneous” phase of narrow-band acoustic signals during their propagation on short near-surface paths under the action of the wind field are presented. The division of the phase into the deterministic, quasi-deterministic (“local”), and random (“turbulent”) components is applied. Histograms of the turbulent component of the phase and result of approximating the histograms by the normal law of the probability distribution are considered. An empirical formula for the relation between the phase variance at different frequencies and variance of the wind velocity on the sound propagation path is derived and compared with theoretical formulas.

AERONET data are used to analyze variations in aerosol radiative characteristics caused by variations in the content of brown and black carbons in smogs of megacities by the example of Beijing, São Paulo, Santiago, and Mexico City. It is shown that the contribution of brown carbon to the imaginary part of refractive index at a wavelength of 440 nm in smogs can exceed the contribution of black carbon by a factor of three. In megacity smogs the spectral dependences of the aerosol absorption optical depth can be approximated by power-law functions with satisfactory accuracy, except in certain Beijing smogs at a wavelength of 400 nm for large relative concentrations of brown carbon. It is shown that the contribution of the coarse aerosol fraction to the total aerosol extinction optical depth in megacity smogs can be from 6 to 20% for wavelengths of 440 and 1020 nm, respectively, and that the contribution to aerosol absorption optical depth can be from 22% for a wavelength of 440 nm to 38% for a wavelength of 1020 nm. The aerosol in megacity smogs differs from the smoke aerosol from large-scale fires in the boreal forests of Russia by increased contribution of the coarse aerosol fraction to the total aerosol volume and by a relatively large imaginary part of the refractive index, and, hence, by a larger absorptance.

Comparison of numerically simulated ozone fields with various experimental data makes it possible to evaluate the quality of models for their use in reliable prediction of variations of the ozone layer. We compared the satellite (SBUV) and ground-based (IFS Bruker 125HR) measurements of ozone content in two atmospheric layers (0–25 and 25–60 km) with the numerical simulation data (obtained using the lowand middle-atmosphere models) over St. Petersburg for the period between 2011 and 2014, namely, the daily and monthly average values of ozone content for 3.5 years (June 2011–December 2014). In general, model describes the experimental ozone content with good or satisfactory accuracy in the two layers. Nevertheless, some systematic differences are found out between the satellite and ground-based data and the results of simulation. In the autumn–winter period, the model usually overestimates the ozone column in the 0–25 km layer as compared to the satellite measurements, and underestimates it in the 25–60 km layer. The same features are observed for daily and monthly average values. In some cases, the model shows strong and high-frequency oscillations in the ozone content, which are not observed in the measurements.

Temperature series from 818 weather stations of the Northern hemisphere of the Earth and the series of solar activity characterized by Wolf numbers during the period from 1955 to 2010 are considered. Opposite acting series components with extreme properties are introduced. The existence of various relations between solar activity and temperature is corroborated. Conditions of their appearance are revealed. The designed approach is suitable for the development of the observational analysis and analytical transformations.

Results of the annual series of complex measurements of carbon dioxide, oxygen, and biogenic elements in the subglacial water in the littoral zone of the southern area of Lake Baikal, carried out from 2004 to 2016, are analyzed. It was found that the plankton photosynthetic activity significantly decreases the partial pressure of carbon dioxide in water (to 240–350 μatm) as compared to the partial pressure of CO₂ in the atmosphere (about 385 μatm) by the end of ice cover season. Hence, the CO₂ flux can be directed only from the atmosphere to the water surface during the ice breakup in the littoral zone of Southern Baikal.

Numerical experimental results characterizing the propagation of multichannel laser radiation in the atmosphere are presented and the possibility of compensating turbulent distortions by use of phase control is considered. It is shown that the effectiveness of adaptive correction depends on the number of channels in the system and on the accuracy of the reference radiation phase reconstruction. The effectiveness can be additionally increased by gain control in each of the channels, i.e., by passing to amplitude-phase control.

Temporal variations in the concentrations of tropospheric ozone in St. Petersburg (Russia), a lowurbanized area in the south of Kirov region (the town of Vyatskiye Polyany), and in the Karadag Nature Reserve in Crimea are presented. The dynamics of ground level ozone concentrations in these regions is analyzed and basic features of the seasonal and diurnal variations are found. The latitudinal dependence of the ground level ozone concentrations is shown.