Advanced Observation for Geophysics, Climatology and Astronomy

1. Introduction

This Special Issue covers a wide range of scientific tasks carried out in the fields of geophysics, climatology and astronomy. The study of various atmospheric layers, their mutual influence on each other and the effect the surface has on them is one of these key tasks. Atmospheric layers are often considered independent atmospheric structures. Nevertheless, these layers are in fact connected by common physics. The influence of physical processes on remote atmospheric volumes has been observed. For example, the results of research indicate the presence of a connection between strong gravitational waves and the appearance of a sporadic layer E in the ionosphere. Evidence has been obtained that daytime gravitational waves and a sporadic E layer are often observed together on the eastern slopes of the Tibetan Plateau in summer [1]. Strong gravity waves generated by volcanic eruptions may have effects on the mesosphere/lower thermosphere. For example, a Hunga Tonga-Hunga Ha’apai volcanic eruption generated perturbations in the mesosphere/lower thermosphere which were associated with the dissipation of primary gravity waves and the propagation of secondary waves [2]. Moreover, in addition to the relief and the volcanic eruption, gravity waves propagating into the stratosphere and mesosphere can be formed by mid-latitude frontal zones or solar activity [3].

One of the most important tasks is to study the physics of processes and phenomena within the different layers of the atmosphere. In particular, the relevance of such research is determined, on the one hand, by the need to search for fundamental physics in the lower, middle and upper atmosphere, the occurrence of atmospheric processes in individual atmospheric layers and their propagation and impact on distant layers. The study of the atmosphere and its underlying surface as a system is relevant for the development of our understanding of climate change and the impact of these changes on various system components [4]. On the other hand, another key task is to find new regions and sites with the required atmospheric characteristics and best atmospheric conditions for placing new optical and millimeter telescopes [5,6].

In addition to these different prospective scientific directions, we can also highlight two further key points. The first is the development of new methods for measuring atmospheric characteristics [7]. The second is the development of models of atmospheric processes with resolutions that cover the smallest scales and energy-carrying atmospheric heterogeneities.

2. An Overview of the Published Articles

In the article “Subsea Methane Hydrates: Origin and Monitoring the Impacts of Global Warming”, the authors examine the structure of the underwater permafrost on the Arctic shelf, taking into account changes in sea level over the past 200,000 years. The presence of climatic changes in the degradation of underwater permafrost and in conditions for the stable existence of subsea methane hydrates in bottom sediments are considered. The East Siberian shelf is chosen as an example here. In order to predict the possibility of developing dangerous climatic scenarios, a method for the seismic monitoring of the state of gas hydrates is proposed, based on solving multiparametric inverse seismic problems.

The article entitled “Crustal Apparent Density Variations in the Middle Segment of the North Tianshan Mountains and Their Tectonic Significance” contains interesting results for the development of our understanding of spatial inhomogeneities in the gravitational field, the formation areas of anomalous pre-seismic signals and earthquake preparation zones. The authors discuss the spatio-temporal variation pattern of the local gravity field within the middle segment of the North Tianshan Mountains. Their comparison of earthquake clusters and gravity anomalies indicates there is a certain relationship between them.

Another study, “Earthquake Prediction for the Düzce Province in the Marmara Region Using Artificial Intelligence”, also aimed at the study of earthquakes. Turgut Pura et al. have used a recurrent neural network (RNN) for the prediction of earthquakes within the Düzce Province of the Marmara Region. In order to train their RNN, they used seismic data (earthquake magnitude, latitude, longitude and depth) provided by the Kandilli Observatory. For the improvement of their RNN, the authors proposed special coefficients depending on the intensity and the number of earthquakes occurring within a space-limited earthquake zone.

In the paper “Atmospheric Electricity Measurements in the Pacific Northwest, Russia” Sergei Smirnov discusses the main reactions of the electric field to meteorological phenomena and seismic and space events. The work discusses the well-known connection between anomalies of the electric field potential gradient and earthquakes [8]. It is indicated that Paratunka Observatory is an excellent site for the accumulation and processing of data in order to study the relationship between atmospheric electricity and earthquakes. It is also worth noting that, currently, measurement data continue to accumulate.

In this Special Issue, a number of studies are devoted to the study of the atmosphere’s microphysical and optical characteristics, as well as the effects of the underlying surface. In particular, Yelena V. Molozhnikova et al. presented the paper “Ecological Zoning of the Baikal Basin Based on the Results of Chemical Analysis of the Composition of Atmospheric Precipitation Accumulated in the Snow Cover”. This study was carried out on the ecology of Lake Baikal [9]. Based on the statistical processing of data and the direct sampling of snow cover, an inventory of the sources affecting the composition of atmospheric precipitation in the region was performed. In the study, the authors separately examined 14 districts. For each district, a set of predominant tracer pollutants was obtained.

The study entitled “Parametric, Semiparametric, and Semi-Nonparametric Estimates of the Kinetic Energy of Ordered Air Motion and Wind Outliers in the Atmospheric Boundary Layer from Minisodar Measurements” expands our understanding of the energy picture in the lower layers of the atmosphere [10]. In particular, the study was carried out within the lower (200 m) part of the atmospheric boundary layer. Using novel approaches developed by the authors, the results of a study of the wind velocity field are presented with high vertical resolution. Vertical changes in the average kinetic energy and kinetic energy of turbulent air flowsare considered separately.

The next article “Climatology of 557.7 nm Emission Layer Parameters over South-East Siberia, Observations and Model Data” is concerned with higher layers of the atmosphere. In the study, a detailed analysis of long-term (2002–2022) variations in the intensity of atomic oxygen’s luminescence in the 557.7 nm line and the night temperature in the mesopause region was performed. These characteristics were evaluated based on measurements by the 10-channel SABER radiometer installed on board the TIMED satellite. This radiometer covers a spectral range of 1.27–17 microns. The data from these measurements are the basis for obtaining vertical distributions of kinetic temperature, pressure, geopotential height, the density volume ratio of $O_3$ (ozone), the emission intensity of OH (hydroxyl) and the concentration of $O_2$ (mol. oxygen).

The article “Measurements and Evaluations of the Atmospheric Transparency at Short Millimeter Wavelengths at Candidate Sites for Millimeter- and Sub-Millimeter-Wave Telescopes” is devoted to the study of the astroclimate. In particular, the astroclimate in the millimeter to submillimeter range is considered. One of the main tasks that the authors were working on is the search for new sites for radio telescopes, which must have an atmosphere with good transparency with respect to millimeter and submillimeter waves [11]. The authors provided results of their comparison of candidate sites for millimeter-wave telescopes in northeastern Eurasia. Different methods for the determination of precipitable water vapor, including artificial neural networks, are discussed.

Two papers—“Influence of Atmospheric Flow Structure on Optical Turbulence Characteristics” and “Simulating Atmospheric Characteristics and Daytime Astronomical Seeing Using Weather Research and Forecasting Model”—are related to the improvement of methods describing the astro-optic and astroclimatic characteristics of the atmosphere. The papers demonstrate the possibility of using the mesoscale WRF model to describe meteorological characteristics at the Large Solar Vacuum Telescope (LSVT) site. The authors presented their simulation results within the Baikal region. The outer domain is 1600 by 1600 km, with a horizontal resolution of 8 by 8 km. The dimensions of the two internal domains are 400 by 400 km and 100 by 100 km, respectively. The horizontal resolution of the inner domain was 500 by 500 m. This modeling was performed for conditions with low average surface wind speeds (1–3 m/s) and for conditions with total cloud cover up to 0.3. It is shown that the selected parameterization schemes for the atmospheric boundary layer (Yonsei University scheme) and the surface layer (MM5-similarity scheme) make it possible to satisfactorily reconstruct variations in wind speed. In order to verify the modeling data on the vertical gradients of the air temperature and vertical shifts in wind speed, measurements of the centers of gravity of solar subimages were carried out synchronously with mesoscale modeling. The analysis of the centers of gravity of the solar subimages was carried out using a well-known differential technique to eliminate the influence of the telescope structure’s mechanical vibrations. The amplitude of the temporary changes in the solar subimages’ centers of gravity is determined by the evolution of turbulent fluctuations of the air refractive index in the direction of radiation propagation. It is shown that the WRF model, despite describing the time variations in the integral of the turbulence energy well (with a correlation coefficient of 0.9), significantly underestimates the amplitude value of the integral along its height.

Additionally, important results have been obtained in atmospheric and adaptive optics. “A Real-Time Measurement System for Atmospheric Turbulence Intensity and Distribution Based on the GLAO System” is devoted to measuring optical atmospheric turbulence using solar adaptive optics. The authors provide a scheme of ground-layer adaptive optics for the measurement of optical turbulence profiles. To determine the strength of atmospheric turbulence at different heights, well-known techniques have been used, including Slope Detection and Ranging (SLODAR)- and Solar Differential Image Motion Monitor (S-DIMM+)-based techniques.

3. Conclusions

It has been shown that the gravitational field within the North Tianshan Mountains region is characterized by the presence of pronounced positive and negative anomalies. The relationship between the probability of an earthquake occurring and the alternation of changes in the gravity field has been determined. In particular, researchers have discussed the correspondence of earthquakes to areas around high-stress zones or anomalous regions that demonstrate alternating positive and negative changes in gravity. For the first time, authors have shown that the Hutubi earthquake was caused by the blind thrusting and associated folding of the overlying strata in the North Tianshan fold-and-thrust belt.

A special recurrent neural network has been proposed for predicting earthquakes in the Düzce Province in Turkey, based on the data collected over the period of 1990–2022. This network has higher prediction capabilities compared to other techniques.

It has been shown that changes in the electric field potential gradient are accompanied by variations of meteorological phenomena and characteristics such as rain, snow, fog, wind speed, air conductivity and the H-component of the magnetic field. The power spectra of the electric fields in the range of atmospheric gravity waves are obtained. These spectra demonstrate a complex nature and contain a large number of maxima in the period from 0.5 to 3 h. The most powerful fluctuations of the electric field correspond to 2–2.5 h.

Based on the processing of measurement data [12], the authors have obtained:

(i)

Spatial distributions of the electrical conductivity and pH in the snow water of Lake Baikal;

(ii)

Spatial distributions of the content of sulfate (${\mathrm{SO}}_4^{2-}$), nitrate (${\mathrm{NO}}_3^{-}$) and ammonium ions (${\mathrm{NH}}_4^{+}$) in the snow cover of the Baikal basin.

Taking into account the percentage distribution of the transfer pathways of air masses calculated from cities, their main source, the authors clarify the picture of pollution formation within the Baikal region. The obtained results are the basis for deeper dependencies between dynamic atmospheric characteristics and the content of atmospheric pollutants.

Minisodar data were used to obtain and analyze spatial and temporal changes in the density vector of the kinetic energy flow of the wind within the lower layer of the atmosphere. Vertical distributions of total kinetic wind energy with and without an allowance for kinetic outlier energy were obtained. These results are a possible foundation for improvements to the empirical and theoretical basis of atmospheric physics.

It is shown that the data of the Sounding of the Atmosphere using Broadband Emission Radiometry and a Fabry–Pérot interferometer, as well as the empirical atmospheric model NRLMSIS, demonstrate good agreement with each other. The authors link the observed differences in time variations to the influence of the underlying layers of the atmosphere, with sudden stratospheric warming causing a slower decrease in air temperature [13]. Moreover, it is possible to assume that the differences in instrumental measurements may be due to other factors associated with the geometry of measurements. Similarly to the data on optical measurements, an analysis of light wave distortions during their propagation from the upper layers of the Earth’s atmosphere to the lower layers and vice versa give different estimations of optical distortion. To a certain extent, these differences are related to the different field of view of the optical instruments and the different paths that optical waves propagate through in the atmosphere.

It was shown that the PWV values estimated from MERRA-2 and water vapor radiometer measurements are in good agreement. Also, temporal variations of PWV derived using neural networks and GNSS data demonstrate a high level of consistency at the Badary station. Researchers obtained probability density and cumulative distributions of 230 GHz zenith opacity at the Terskol peak and at the Suffa plateau. According to the researchers, these distributions confirmed that the best transparency (among the considered sites in Russian territory) was found at the Terskol Peak Observatory. The results presented in these works allow us to say that optical transparency conditions are somewhat better in the Sayan Mountains (Khulugaisha Peak) and in Altai (Tashanta) (for comparable altitudes above sea level) [14,15].

For the first time, we carried out studies of the structure of atmospheric flows in individual regions of Russia using the mesoscale WRF model, with the aim of assessing and short-term forecasting atmospheric characteristics, including mesoscale atmospheric turbulence and small-scale (parameterized) turbulence. The modeling of vertical profiles of wind speed, temperature and air humidity was performed up to a height of 25 km within a wide region above the Sayan Solar Observatory and the Baikal Astrophysical Observatory. We successfully performed a series of experiments to reconstruct the wind speed field at a horizontal resolution of 500 m in the internal domain of the WRF model within this macroregion. Based on the modeling results, it is shown that the boundaries of Lake Baikal and the Angara River valley are clearly visible in the wind speed field. This demonstrates the correctness of the modeling of the temperature, humidity and wind fields. Using the WRF model for the first time in the Baikal Lake Basin, mesoscale vortex structures with anticyclonic air flows during the daytime were discovered in the atmospheric boundary layer, affecting the quality of astronomical images. Analysis of the horizontal energy spectra showed that the characteristic scales of this mesoscale vortex structure, the center of which is formed north of the BAO, vary from 10 to 20 km. The modeling results show that upward air movements in the lower atmosphere are suppressed both above the cold surface of Lake Baikal and within these mesoscale eddy structures. It was shown for the first time that the turbulence over the BAO significantly depends on the orography and characteristics of mesoscale atmospheric disturbances (mesoscale eddies and jets). The best reproducibility of local air circulation during the day corresponds to the YSU parameterization scheme. Using the WRF model, vertical profiles of wind speed and air temperature over the BAO under clear-sky conditions were obtained and detailed. Using the vertical profiles of these characteristics, vertical profiles of optical turbulence were reconstructed. The first attempts at short-term forecasting showed a good reproduction of the changes in surface atmospheric characteristics (primarily wind speed), but significant deviations in amplitude were often observed. In addition to wind speed, the WRF model was able to adequately describe the time variations in the characteristics of the integral turbulence energy in a layer up to 20 km thick (with a correlation coefficient of 0.9), but significantly underestimated the amplitude of the optical turbulence integral along the height. The difference in amplitude is associated with a rather rough relief model and the applicability conditions of physical processes’ parameterization schemes.

A special system for measuring optical distortions and estimating the vertical profiles of optical turbulence up to an altitude of about 20 km was proposed. This system was implemented on the New Vacuum Solar Telescope (NVST). By processing the measurement data obtained from the New Vacuum Solar Telescope, it is shown that the SLODAR method’s accuracy in determining vertical profiles is approximately 93%. The accuracy of the S-DIMM+ method is slightly lower, at 87%. The S-DIMM+-derived values of optical turbulence strength are lower than the strengths obtained using the SLODAR method. The turbulent layer at heights near the tropopause is not distinguished.