Home – Home – Jornals – Atmospheric and Oceanic Optics 2025 number 10

Due to degradation of laser beam properties on atmospheric paths, the maximum length of communication lines is limited. In this regard, it is of interest to evaluate the possibility of detecting the topological charge of a vortex beam disturbed by atmospheric fluctuations using wave front sensors. The problem of measuring the wavefront tilts of a vortex laser beam propagating along a path in a turbulent atmosphere by a Shack-Hartmann sensor is considered. Estimates are obtained for the change in the angles of local tilts of wavefront associated with the solenoidal component of the Poynting vector and the influence of turbulent fluctuations of the refractive index of the atmosphere. Using several specific models of the Shack-Hartmann sensor as an example, the possibility of calculating the value of the topological charge of a vortex Laguerre-Gaussian beam from the measured angles of local wavefront tilts is investigated.

Based on the representation of the solution of the stochastic Helmholtz equation in the form of a path integral (Samelsohn G., Mazar R. Phys. Rev. E. 1996. V. 54, N 5) for the Kolmogorov model of the turbulence spectrum, an expression for the spatial coherence function of a spherical wave propagating in a turbulent atmosphere is derived under the assumption that the geometric-optical approximation is valid for a random phase incursion in the path integral. Estimates of the corrections to this approximation by order of magnitude are found. The obtained formula has no restrictions on the wavelength and the angle between the observation points that arise when using the parabolic and Markov approximations. The error in estimating the radius of spatial coherence in the parabolic approximation, arising from the sphericity of the wave front with an increase in the angular separation of the observation points, is calculated. It is shown that the error increases with the wavelength, and for millimeter and longer waves it can lead to an overestimation of the scale of spatial coherence of a spherical wave by few times.

Water vapor is a significant component of the Earth's atmosphere. Assessing the contribution of water vapor to the Earth's radiation balance has remained a topical issue for decades. In this work, the water vapor self- and foreign-continuum spectra have been retrieved at temperatures of 310, 325, and 340 K in the 1600 cm^-1 absorption band for the first time based on earlier Fourier-measurements of water vapor absorption under self-broadening and broadening by air at 296-340 K within this absorption band with the use of HITRAN2020 spectroscopic database. The retrieved spectra show characteristic for self- and foreign-continuum spectral and temperature dependences. The spectra we retrieved are compared with the MT_CKD semi-empirical continuum model and the semi-empirical dimer-based continuum model ( Simonova A.A., Ptashnik I.V., Shine K.P. Semi-empirical water dimer model of the water vapour self-continuum within the IR absorption bands // J. Quant. Spectrosc. Radiat. Transfer. 2024. V. 329. P. 109198-1-19. DOI: 10.1016/j.jqsrt.2024.109198). The results are important from both fundamental, within the molecular spectroscopy, and practical point of view, in problems of atmospheric modeling and remote sensing.

Ergodic theorems are important when comparing measurement results with theoretical conclusions. Compilation of a “statistical ensemble" requires numerous experiments under similar conditions, which is practically impossible. Therefore, average values are necessarily derived from the measurement data of a single experiment by averaging the empirical data over a certain time range or spatial region. The question of how close such empirical averages are to probability averages is answered by so-called ergodic theorems. An ergodic theorem for stationary processes was proved by G. Taylor in 1922. In this work, we have proved an ergodic theorem for the case of non-stationary random processes. The proof confirms the ideas of O. Reynolds (1894), according to which the time averaging interval should be large compared to the characteristic periods of a pulsation field, but small compared to the periods of the averaged field. The cause of the drift of the mean value, which consists in the dependence of the average values of hydrodynamic fields on averaging interval length and significantly complicates the determination of empirical average values, is found. An approximate measure for quantitative assessments of this phenomenon is suggested; the existence of an averaging time at which the influence of this phenomenon is minimal is shown. The results are important for studies of atmospheric turbulence, where all hydrodynamic elements are non-stationary and show pronounced daily and annual variations.

Aerosol turbidity of the atmosphere over Antarctica is the lowest on the planet. However, it shows regional peculiarities in the temporal variability. In this paper, the main features of the interannual and seasonal variations in the aerosol optical depth (AOD) are revealed on the basis of the analysis of its long-term measurements at Mirny Station. Pronounced variations with a period of 5-6 years and amplitude of 0.005 relative to the average level of 0.023 in the interannual variability of AOD (0,5 mm) are shown. The annual variation in AOD of fine aerosol is characterized by spring and summer maxima (October and February), and that of coarse aerosol is characterized by one summer maximum. Approximation formulas are proposed that make it possible to estimate the monthly average values of spectral AOD in the wavelength range 0.34-2.14 mm.

Bio-optical parameters of seas of the Far East region obtained from the MODIS/AQUA radiometer data are analyzed. The results of two main atmospheric correction algorithms based on the following assumptions are compared: the absence of water-leaving radiance in the near-infrared spectral bands and the stability of the sea water spectral shape in this range (MUMM). Verification was carried out using data of Japanese and Korean AERONET-OC stations. An approach to improving the results of MUMM atmospheric correction by using a regional adjustment of the color indices is considered. The MUMM correction after adjustment is not inferior to NIR correction in terms of the calculation accuracy of chlorophyll- a concentration. It was found that the recommended NIR correction leads to negative reflectivity coefficients Rrs at a wavelength of 412 nm in 10% of cases. These cases correspond to highly trophic waters and are accompanied by an overestimation of the chlorophyll-a concentration by an average of 1.8 times. The proposed correction of the color indices does not lead to negative values of Rrs; the color indices in the blue spectral range have significantly lower errors than those of the NIR algorithm. The proposed approach ensures more reliable estimates of bio-optical parameters of the sea based on satellite data.

Wind Doppler lidars have proven themselves as an effective means of evaluating wind turbulence in aircraft measurements. However, existing methods of sounding from aboard an aircraft assume the presence of a complex scanning system. In this work, we test possibility of evaluating turbulence parameters and wind convective flows using the second version of the lidar created in the Laboratory of Wave Propagation of IAO SB RAS during nadir sounding from aboard a flying aircraft. Based on the analysis of experimental data, we retrieved vertical profiles of estimates of vertical wind velocity (VWV) dispersion and turbulent kinetic energy dissipation rate up to altitudes of 1250-1600 m. During the analysis of sounding data near clouds, we recorded VWV shear according to one lidar signal spectrum, which contained two Doppler peaks. The results of this work can be useful in creating new methods for evaluating turbulence and wind shear.

Characteristics of a convective cloud with heavy rainfall over Saint-Petersburg and Leningrad region on 1st of July, 2023, are considered. The analysis was based on data of the weather radar DMRL-C, weighing precipitation gauges Pluvio² 200, and two lightning detection networks. The appearance and development of Cb under study was a result of merging two convective clouds. During their development the clouds slowly converged moving towards Saint-Petersburg from the southwest. Measurements have shown that the cloud merging led to explosive growth of the cloud top, which reached an altitude of 13.4 km; significant increase in the maximal reflectivity up to 69 dBZ, in volume of the cloud supercooled part with high reflectivity, volumes of the cloud with graupel and hail, precipitation intensity up to 140 mm/h, and lightning rate. The appearance of “the cloud bridge” was recorded. It has been shown that it consisted of graupel and wet snow particles.

Correct assessments of greenhouse gas fluxes and the global carbon cycle require well-provided data on greenhouse gas sources and sinks in the surface - atmosphere system at various natural sites. The article summarizes the results of shipboard measurements of carbon dioxide concentration in surface water throughout the water area of Lake Baikal received in eight spring campaigns of Limnological Institute, Siberian Branch, Russian Academy of Sciences. Spring period is of particular interest for research, since due to the large geographical extent of the lake from south to north, after the opening of the ice cover, the water gradually warms up. This makes it possible to take measurements in relatively different “seasons" during a time-limited expedition. Against the background of a noticeable interannual variability in the spatial distribution of CO₂ concentration in surface water in spring, its decrease from the Southern to the Northern basins of the lake is pronounced. While moving away from the coastal zone to the central part of the water area (to depths of more than 200 m), the concentration of dissolved carbon dioxide increases. The results of the study are of interest to specialists in climate issues and biologists, since carbon dioxide is one of the integral components of the carbon cycle during photosynthesis of aquatic plankton in the Baikal water.

The work is devoted to the study of the effect of aerosols on various processes in the atmosphere, in particular, the formation of convective clouds and their electrification. The special cases of thunderstorms in the Krasnoyarsk Territory during wildfires are considered. This region is characterized by the highest risk of increased wildfires due to the climate change among Russian regions. The thunderstorm events were selected based on the analysis of lightning activity in the selected area from 2015 to 2022 in comparison with wildfire data. A series of numerical experiments on simulating thunderstorms in the WRF model with different aerosol concentrations in the atmosphere have been performed. Based on the simulation results, electrical parameters of clouds have been calculated. To find correlations between the density of lightning discharges and the parameters of convective systems we suggest methods for estimating lightning activity based on the volume of thunderstorm cells with a certain radar reflectivity and the area of high electrical potential. We have revealed that an increase in the aerosol load in the atmosphere increases the time of convection development, as well as a significant effect of aerosol concentration on electric potential maximum at near constant radar reflectivity maximum. The results can be used to develop fundamental ideas about the relationship between lightning activity and wildfires and to improve methods for predicting lightning activity.

The problem of atmospheric emission source identification using remote sensing data is considered. An algorithm is proposed for a three-dimensional model of atmospheric pollutant transport and a nonlinear measurement model represented as a “differentiable black box". The algorithm is based on sensitivity operators and ensembles of adjoint equations solutions. It was tested on a realistic scenario for identifying soot sources for the Baikal region with synthetic satellite measurements of the Terra/MODIS platform, which showed its applicability. Additionally, the measurement data decomposition modification of the algorithm is proposed, which made it possible to reduce the relative error of retrieving the source function by 12% compared to the version without decomposition. The results can be used in the development of remote sensing data processing systems.

In atmospheric remote sensing, particularly in the interpretation of lidar signals from cirrus clouds, the accuracy of light scattering modeling on non-spherical randomly oriented ice particles plays a crucial role. Although the physical optics approximation is commonly used due to its computational efficiency, it does not always provide sufficient accuracy, especially when particle sizes are comparable to the wavelength of incident radiation. This introduces systematic errors into scattering matrix databases used for solving inverse problems. This study employs the discrete dipole approximation to verify the validity of the physical optics approximation. The primary focus is on comparing results obtained at wavelengths of 0.532 and 1.064 mm for particles of various shapes and sizes from 2 to 8 wavelengths. It is shown that in this size range, the physical optics approximation leads to relative errors of up to 20% in the linear depolarization ratio and reduces the backscattering intensity by half. The findings enable a more precise estimation of the applicability limits of the physical optics approximation and provide corrections for existing scattering matrix databases. This, in turn, will improve the accuracy of lidar data interpretation and enhance the quality of microphysical retrievals for cirrus clouds.

Highly directional supercontinuum (HDSC) is a unique source of broadband coherent radiation. To create such a source, it is necessary to know the parameters and conditions of its occurrence. The article presents the results of experimental study of the conditions for HDSC generation in gaseous nitrogen pumped by a radiation pulse with wavelength of 950 nm, duration of 70 fs, and energy of 3-6 mJ. The pump radiation was focused into a gas chamber by a spherical mirror with F = 75 cm under aberration conditions (the angle of incidence of the radiation on the mirror was 15°). It is shown that there is optimal pump energy of 4.5 mJ and gas pressure of 3-4 atm. The spectral composition of the HDSC covers the range from 350 to 1000 nm. The divergence of HDSC radiation is diffraction-limited and its greatest value (the diameter of the white spot in the far zone) corresponds to a wavelength of 780 nm. The maximal HDSC energy was 17 μJ. The results are useful for understanding the physical mechanisms underlying the emergence of HDSC, as well as for developing broadband coherent radiation sources.