Home – Home – Jornals – Atmospheric and Oceanic Optics 2025 number 2

The parts of the water vapor continuum absorption conditioned by different physical mechanisms are investigated. The difference between the water vapor continuum absorption calculated according to the asymptotic line wing theory and that found from experiment is the sum of absorption by stable dimers and absorption due to some other absorbing objects. This “unidentified” absorption was found for intervals centered at 8800 and 10600 cm^-1. The spectral behavior of the “unidentified” absorption turned out to be similar to that obtained in the case of modeling the continuum absorption by H₂O dimers through the equilibrium constants of the corresponding reactions. The difference in the unidentified absorption curves found by the two methods can be considered a lower limit of absorption by the monomer wings. Among the graphs available in GrafOnto information system, graphs were found that were qualitatively similar to the unidentified absorption. The results can be considered encouraging, but not final, since the system contains only a limited set of substances.

Identifying the types of atmospheric aerosols plays a significant role in evaluating the influence of aerosols on the climate system, identifying aerosol sources, and improving aerosol satellite retrieval algorithms. At present, there are various ways to classify aerosol particles, but most of them do not take into account regional characteristics. Based on the archival data of photometric observations of the robotic monitoring network AERONET in Middle Urals, a version of classification of the main types of aerosol particles is suggested. The classification was performed by the spectral values of the aerosol optical thickness by the method of k -medians. The initial centers of clusters were defined by spectral values of extinction coefficient calculated with MOPSMAP package from the regional aerosol model MUrA and the global model CALIPSO. Five types of aerosols were identified: Dust, Clean Continental (background), Polluted Continental/Smoke, Polluted dust, and Elevated Smoke. Analysis of data showed that Clean Continental and Dust aerosols are most common in the Middle Urals (26 and 25% of observations, respectively), while the presence of Polluted Continental/Smoke accounts for 20%. The suggested approach makes it possible to significantly supplement the information obtained by spectral ground-based photometric measurements.

The article presents the results of aircraft lidar measurements of the spatial distribution of the relative concentration of chlorophyll- a in the surface waters of the Kara Sea. The chlorophyll concentration was determined by the laser-induced fluorescence method. For normalization, the intensity of the Raman scattering signal of water radiation was simultaneously recorded. The results of the spatial distribution of the normalized fluorescence intensity were obtained at three sites in the southwestern region of the Kara Sea. For two sites in the shelf zone near the western coast of the Yamal Peninsula, the spatial distribution of the fluorescence intensity is quite uniform with variation coefficients of 9 and 15%. The third site in the northern tip of the Yamal Peninsula is characterized by a strong influence of continental river runoff, which is manifested in the presence of sharp frontal zones with scales of 5-10 km, where the variation coefficient of the normalized fluorescence intensity Cl reaches 40%. The variation in Cl values in this section is mainly due to the strong variability of the Raman normalization signals and, to a much lesser extent, to the change in fluorescence intensity. Factors influencing the variability of Raman signals are considered. Synchronous in-situ measurements from a ship and remote measurements from an aircraft allowed us to estimate the dimensional calibration coefficient k_Cl = 1.03 ± 0.09 μg/l for the first two sections of the Kara Sea surface water sounding.

The results of microwave observations of ozone in the middle atmosphere at Apatity (67° N, 33° E) in winter 2022/2023, during a period of high solar activity in the 25th cycle, are presented. A mobile ozonemeter with an operating frequency of 110.8 GHz was used in the measurements. The device had a single-sideband noise temperature of 2500 K, which made it possible to track variations in O₃ with a 15-min resolution in the middle atmosphere. Estimates of the ozone vertical profile at altitudes of 22-60 km have been made. These results were compared with satellite MLS/Aura data on the altitude profiles of ozone and temperature. This report discusses the behavior of ozone in February-March 2023. Ozone variations took place during the sudden stratospheric warming (SSW) which occurred in mid-February and was accompanied by an extraordinary increase in the total ozone content (TOC) from 240 to 500 DU. The limits of ozone changes at altitudes of 25, 40, and 60 km are given. The influence of the intense geomagnetic disturbance (storm) on March 23-24 on the daily variation in ozone at an altitude of 60 km is discussed.

One of the indicators of ongoing climate change is the evolution of cloud regimes, both in individual regions and globally. Within this framework, the long-term variability in the structure of multilayered clouds with an optical thickness of less than 15 over Western and Eastern Siberia during the summer and winter seasons from 2006 to 2023 in daytime conditions is estimated based on CALIOP lidar data (CALIPSO satellite). Multilayering refers to the presence of clouds in several levels at the same time located under each other with gaps between them. The applied methodology is based on the use of cloud classification results from daily CALIOP lidar measurements, calculation of seasonal recurrence values for each combination of cloud types in multilayer structure, deriving time series, determining trends, and evaluating their parameters. It was found that the fractions of clouds with different numbers of layers over both regions did not significantly change during the period under study. In Western Siberia, the proportion of double-layer clouds is 68% in summer and 71% in winter, while in Eastern Siberia, 71 and 75%, respectively. The fraction of three-layer clouds reaches 27% in summer and 25% in winter in Western Siberia and 26% and 23% in Eastern Siberia. The fractions of four- and five-layer clouds do not exceed 5% in both regions together and are almost the same in the two seasons. The most frequent combinations in the multilayer clouds over Western and Eastern Siberia were determined. Estimates of linear trends in the fraction of the most frequent variations in multilayer clouds over the period under study are presented. The results can contribute to improving the accuracy of climate models and radiative transfer estimates.

The study of cirrus clouds is currently under close attention since they play an important role in the formation of the Earth’s climate. Their study is mainly conducted through laser sounding of the atmosphere. The interpretation of laser sounding data requires an adequate optical model of cirrus clouds. However, most existing optical models are developed assuming a random spatial orientation of particles, which, according to recent experimental data, is often inaccurate. We suggest an optical model of cirrus clouds which considers the preferential horizontal orientation of particles within a cloud. The model includes ideal hexagonal plates and columns and hollow columns as quasi-horizontally oriented particles. Additionally, the model incorporates hexagonal plates and columns, droxtalls and bullites, irregularly shaped particles, and aggregates of such particles as randomly oriented particles. The results are crucial for developing algorithms of lidar data interpretation when investigating cirrus clouds.

Method for detecting most forms of altocumulus, stratocumulus, and cumulus clouds and their middle (4-7) and high (8-10) amount is proposed. The method is based on statistical analysis of continuous series of measured global horizontal irradiance. Clouds are classified into two classes according to their influence on the heterogeneity of the formed series. The analysis uses the coefficient of variation and the range of sample. Testing of the method showed that cumuliform clouds are detected with accuracy of 94% at sample completeness of 63%, and the cloud amount is assessed with an error of less than 21%.

An integral component of any analyzer is a sensor. Interest in the development of highly efficient sensing elements for detecting various substances in the surrounding atmosphere remains strong. Among many types of sensors, optical sensors capable of operating in laser mode stand out due to their superior sensitivity compared to fluorescent sensors. This study describes the sensory properties of a photo-excitable active waveguide with a polymethyl methacrylate matrix doped with Nile Red dye. The threshold characteristics of the dye laser generation are investigated. Sensitivity is shown for 0.8% carbon dioxide in an argon mixture and 0.8% nitrous oxide in an argon mixture at atmospheric pressure within the active waveguide under lasing conditions. Possible mechanisms for reducing the lasing threshold in the presence of detectable substances are discussed.

Surface inspection under large strains is a critical problem for both civil and mechanical engineering. Optical techniques can be used for its solution. Digital image correlation (DIC) is one of these promising optical techniques. It is used to measure displacement and strain fields without contact with the specimen surface. Input parameters can directly affect the strain field calculation accuracy. The correlation method is a key parameter in strain field calculation based on DIC, especially under large strains. In this work, three spatial and incremental methods are tested; their accuracy and applicability are estimated; their advantages and drawbacks are discussed. The results can be useful for the developments of means for non-destructive testing.

A laser guide star is an essential part of the adaptive optics system of a ground-based optical telescope. The main limitation of sodium laser guide stars, formed on the basis of the resonant fluorescence of mesospheric sodium atoms, is the low brightness of the LGS. To estimate a possibility of creating LGS based on the fluorescence of other metals in the mesosphere, the efficiency of excitation schemes for atoms of potassium and nickel are calculated. The relative backscattering flux of fluorescence for transitions of potassium and nickel atoms is calculated taking into account the content of the atoms in the mesosphere and the transmission of the atmosphere. The comparison with the results for sodium atoms is made. Our results can be used for the development of adaptive optics systems with artificial reference sources for ground-based telescopes and mesospheric lidars.

A laser guide star is an essential part of the adaptive optics system of a ground-based optical telescope. The main limitation of sodium laser guide stars, formed on the basis of the resonant fluorescence of mesospheric sodium atoms, is the low brightness of the LGS. To estimate a possibility of creating LGS based on the fluorescence of other metals in the mesosphere, the efficiency of excitation schemes for atoms of iron are calculated. The relative backscattering flux of fluorescence for transitions of iron atoms is calculated taking into account the content of the atoms in the mesosphere and the transmission of the atmosphere. The comparison with the results for sodium, nickel, and potassium atoms is made. Our results can be used for the development of adaptive optics systems with artificial reference sources for ground-based telescopes and mesospheric lidars.