Atmospheric and Oceanic Optics最新文献

Two spring events of abnormally low dissolved oxygen concentrations in surface waters of the northwestern Black Sea were detected over a hundred-year period in [26]. The presence of the first extreme in the 1920s and 1930s was explained by an abnormal increase in temperature, and the second extreme in the last decades of the 20th century was explained by eutrophication. This work shows that the decrease in dissolved oxygen concentrations in the upper 10-m layer coinciding in time with the warming in the first third of the 20th century was caused not only by abnormally warm climatic conditions, but also by extremely low river runoff into the northwestern Black Sea in that period. Reduced discharge of fresh river waters saturated with oxygen (especially pronounced during the period of increased runoff in spring) was one of the reasons of an increase in the salinity of the surface sea layer and a sharp decrease in the concentration of dissolved oxygen. Direct measurements have shown that water transparency on the northwestern shelf of the Black Sea increased in the first third of the 20th century, confirming the weakening of the influx of turbid river waters during that period.

This paper presents the results of an experimental study of laser generation based on electron transitions in neutral krypton atoms in the near- and mid-infrared spectral regions, pumped by a pulsed inductive longitudinal discharge of a low-pressure gas active medium. Particular attention is given to the investigation of population inversion formation conditions and experimental studies of the influence of gas mixture compositions (Kr–Ar, Kr–He, Kr–He–Ar), gas pressure, and discharge parameters on the energy, temporal, and spatial characteristics of the laser generation. For the first time, laser generation at a wavelength of 810 nm (corresponding to the 5p → 5s transition of Kr I) was recorded in a pulsed inductive longitudinal discharge at an optimal pressure of approximately 0.05 torr. Laser generation on 4d → 5p and 6s → 5p transitions (at 1442, 1476, and 2524 nm) was also detected in pure krypton at pressures around 1 torr. Temporal lasing characteristics were investigated, showing that the optical pulse duration was 6 ± 1 ns (FWHM). The spatial beam profile had an elliptical shape with dimensions of approximately 6 ± 0.2 × 5.2 ± 0.2 mm. The pulse lasing energy did not exceed 3 μJ, corresponding to a peak power of about 600 W.

The results of the study of the elemental and charge composition of the plasma of a vacuum arc discharge with a cathode made of magnesium Mg are presented. Time-of-flight spectrometry was used to determine the mass-charge composition of the ion current extracted from the vacuum arc plasma. The spectral characteristics of the discharge plasma were studied by recording the power density distribution of its radiation in the optical spectral range. Both methods were used simultaneously, so that a high level of identity was maintained not only in the operating conditions of the vacuum arc, but also in the true composition of the plasma of the cathode spots, which are the elementary cells of the structure of such a discharge. It was found that the fractions of heavy charged particles, represented by single- (Mg⁺) and double-charged (Mg²⁺) magnesium ions, in the beam extracted from the expanding plasma, depend significantly on the average energy deposited in the discharge. With the increase of the average energy the fraction of Mg²⁺ decreased, while that of Mg⁺ increased. In turn, the relative amplitudes of the lines of ions (Mg II and Mg III) and atoms (Mg I) of magnesium in the emission spectra of the plasma of cathode spots did not depend on the discharge energy characteristics. Based on the obtained results, reasoning is given about the mutual complementarity of the methods used and the further development of methods for diagnostics of cathode arc plasma.

Solar-induced fluorescence is an index of plant photosynthetic activity, promising for monitoring ecosystem productivity on a global scale. In this work we present estimates of photosynthetic activity of the main phytocenoses in the south of Western Siberia (grasslands, deciduous and light coniferous forests, croplands, and wetlands), using TROPOMI satellite data for the period of 2018–2024. Employing ERA5-Land reanalysis data and products, obtained from MODIS and CERES measurements, we studied the correlations between solar-induced fluorescence and the main temperature-moisture environmental parameters, vegetation indices, and photosynthetically active radiation, as well as directly between these characteristics themselves (spatial resolution is 0.05°, and time resolution is 1 month). The presented results describe the specific features of these interrelations both for the main phytocenoses of all target area, and their latitude variations for grasslands and deciduous forests.

Atmospheric turbulence is one of the most significant factors affecting the propagation of waves of various nature and the operation of devices based on their application. This paper presents the results of experimental studies of the impact of short-term heavy rainfall on subsequent changes in the meteorological and turbulent state of the ground atmosphere based on processed synchronous acoustic and optical measurements of atmospheric parameters. An assessment is made of the impact of intense precipitation on the main turbulent characteristics of the surface atmosphere, such as the energy of temperature and wind fluctuations and vertical heat and momentum fluxes. It is shown that heavy rainfall significantly changes these characteristics. The results obtained can be used to interpret optical and acoustic measurements used to study the atmosphere.

Quantitative analysis of the gas mixture absorption spectra is complicated by noise. The parameters of standard filters are related to the entire analyzed spectral range. This means that the filter parameters being optimal for strong absorption lines are not optimal for weak absorption lines and vice versa. An approach to create adaptive filter for denoising experimental spectra based on the combination of a windowed version of a standard filter with the independent component analysis is suggested and implemented with the Savitzky–Golay filter as an example. The numerical simulation was carried out at normal conditions for the absorption spectra of the model of mid-latitude summer atmosphere in the 100–1000 GHz spectral range. The efficiency of the suggested adaptive and the standard versions of Savitzky–Golay filter was compared using a quantitative criterion of the proximity between two spectral curves. Experimental validation of efficiency of the suggested adaptive Savitzky–Golay filter was conducted on the example of 200 ppm SO₂ and 10 000 ppm H₂O gas mixture. The SO₂ concentration was evaluated using multivariate curve resolution method. The relative error in the concentration retrieved after noise reduction by this filter was 3.7 times less compared to the standard Savitzky–Golay filter. Thus, the suggested adaptive Savitsky–Golay filter makes it possible to increase the efficiency of denoising experimental spectral data.

The morphology and composition of aerosol particles determine their activity in atmospheric heterogeneous processes and affect the radiation and chemical properties of the atmosphere. However, there is still insufficient information about the morphological characteristics of atmospheric aerosols. This work studies mineral composition of dust aerosol particles and identify natural and anthropogenic components in aerosol composition in the surface air layer in Moscow metropolis in winter. Microparticles containing a lot of potentially toxic elements, such as heavy metals and metalloids of anthropogenic or mixed origin, were found. Several groups of metal-containing microparticles in near-surface aerosols were identified, the most common of which were: (1) sulfates (mainly Ba and Sr); (2) sulfides (Fe, Sb, and Pb); (3) oxides (Fe, W, Cu, As, Cd, and Pb); (4) intermetallides (Pb–Sn–Zn, Pb–Zn, Cu–Zn, Cu–Pb, Te–Sb–Al–Bi, and Fe–Ni–Cu–Sn–Fe–Cr–Ni); (5) native metals (Pb, Zn, Ni, Te, Fe, Zr, and W). The distributions of different elements over the surface of a filter with an aerosol sample was estimated. It was found that most of microminerals in dust particles were in the calcium phase, and to a lesser extent, in silicate and aluminosilicate phases. The results complement information on the morphology and micro-mineral composition of aerosols in the near-surface air of a megalopolis and can be useful both for clarifying the role of aerosol particles in atmospheric heterogenic processes which change the climate and for solving applied environmental problems.

The thickness and spatial distribution of a methane hydrate stability zone (MHSZ) associated with submarine permafrost is estimated based on numerical simulation. Using CMIP6 ensemble model calculations with a scenario of high anthropogenic greenhouse gas emissions (SSP5-8.5), a weak dependence of MHSZ shrinkage on ongoing warming is found, and mainly on the side of its base. This process is, first of all, a consequence of the Holocene marine transgression and depends on geothermal flux intensity. The spatial distribution of methane fluxes from bottom sediments caused by degradation of gas hydrates under the violation of their existence conditions is derived. The intensity of methane emission from seafloor to water is estimated at 15 Tg/yr in the modern period and 16–17 Tg/yr to 2300 (similar estimates of the intensity of methane emission from water to the atmosphere are not made in this work). Significant changes in the intensity of methane emissions from seafloor to water are hardly probable for at least several thousand years. The resulting fields of methane fluxes from bottom sediments can be used in numerical ocean models for assessing methane emissions to the atmosphere.

Studying the occurrence of sudden stratospheric warmings (SSWs) and their complex interrelation with tropospheric and stratospheric processes is of fundamental value for improving of our understanding of the dynamics of atmospheric circulation. This is especially important under phenomena but of global climate changes, which not only increase the frequency of anomalous atmospheric phenomena, but also intensify them. Based on a developed and adapted method for identifying Rossby wave breaking (RWB), which accounts for the specifics of stratospheric circulation, an analysis of the conditions for the occurrence of major SSWs in the Northern Hemisphere was conducted. The method relies on examining the geometry of potential vorticity contours in the stratosphere at the 850 K level using ERA5 reanalysis data. It is shown that anomalous RWB processes in November and December play a key role in preconditioning the onset of SSWs. Most of the analyzed SSW events are associated with an increase in the number of RWB events in the Asia-Pacific (AP) region in November and December, and occasionally in January. In cases where SSW initiation is linked to RWB over the Atlantic and Europe, it is also preceded by RWB anomalies in the AP region. For the identified types of wave breaking in the stratosphere, atmospheric blocking is characteristic in the troposphere, accompanied by negative near-surface temperature anomalies over Eurasia and/or North America. The increased frequency of early- and midwinter major SSW events aligns with the previously identified trend of enhanced negative temperature responses to atmospheric blocking in the Northern Hemisphere. The results of the work can be used to improve the prediction of SSWs and the associated extreme weather events, as well as for climate modeling to account for the RWB effects on stratospheric processes.

The atmospheric transformations of vegetation-emitted organic compounds are initiated by their interaction with photolytically generated short-lived free radicals. The chain process, which is a sequence of radical stages, leads to the formation of condensable products as the nuclei of aerosol phase. The free radicals generated during the photolysis of benzaldehyde and biogenic aldehydes, including aromatic ones (salicylic, ortho- and para-anisic), were identified under laboratory conditions. Chromatographic analysis of the products formed after the introduction of additional free radicals shows that the composition and amount of condensable products change. The field measurements of the concentrations of aldehydes and the products of their photochemical decomposition under sunlight were carried out, and the compounds formed in the interaction of initial aldehydes with free radicals were detected. These products can be employed to estimate the concentrations of free radicals even below the limit of radical detection by physicochemical methods. The rates of free radical generation and sink were shown to change with altitude in the troposphere. The approach taking into account the vertical transport of air masses and the corresponding changes in photolysis rate constants has been developed. The formation of condensable products is the chain termination stage in the whole process of atmospheric photonucleation of biogenic aldehydes. The new data on the altitudinal variation in the concentrations of short-lived free radicals allow calculating photonucleation rates for biogenic aldehydes at different altitudes. The developed kinetic schemes can be used to simulate the formation of organic atmospheric aerosol in the troposphere taking into account the vertical transport of air masses.