Izvestiâ Akademii nauk SSSR. Fizika atmosfery i okeana

An attempt has been made to relate the morphological characteristics of intense convective vortices, such as waterspouts and dust devils, to their hydrodynamic stability. The symmetric stability of cyclostrophically balanced vertical baroclinic vortices, whose radius of maximum wind depends on height, is considered. It shows the stability of narrow vortices, nearly cylindrical at the bottom, with a radius that then increases with height at an increasing rate and becomes infinite at a finite level above the Earth’s surface. On the contrary, wider conical vortices satisfy the necessary condition of instability, and it is hypothesized that this partly explains the more diffuse, disorganized nature of this kind of dust devils. The possibility of taking into account the general rotation in the problem is considered.

The paper presents study of the parameters of wave-like structures based on the data of long-term continuous sodar monitoring of the atmospheric boundary layer (ABL). Submesoscale internal gravity waves (IGWs) of non-orographic origin trapped in a stably stratified ABL (SBL) are considered. Statistical data on the parameters of two classes of IGWs are presented: internal gravity-shear waves (IGSWs) of the Kelvin-Helmholtz billow (KHB) type and buoyancy waves (BW). Identification and classification of IGWs was carried out by the visual analysis of sodar echograms. The measurements carried out in the Moscow region were used. The seasonal and diurnal variability of the frequency of registration of waves of both classes were studied, the values of the parameters of the observed waves were analyzed, and the ranges and average values of these quantities were compared.

The analysis of changes in the snow cover extent S in Eurasia was performed using the results of simulations with the ensemble of global climate models of the international project CMIP6 under the scenario of anthropogenic impacts SSP2-4.5 for the 21st century. Features of S variability in relation to changes in surface air temperature T in different seasons are revealed by comparison of ensemble model calculations for the “historical” scenario to CDR satellite data against the background of a general decrease in the snow cover extent in Eurasia during the contemporary warming. It is noted that the multimodel ensemble mean estimates of the sensitivity parameter dS/dT for the transitional seasons in spring and autumn can be significantly lower in absolute values than those for the individual models and those derived from the satellite data. Comparison of model estimates with satellite observation data showed that the models generally reproduce the observed variations in the snow cover area in Eurasia, while variations in the area may be underestimated for individual models. According to ensemble model calculations, the rate of snow cover reduction in Eurasia in the second half of the XXI century decreases compared to the first half of the XXI century for all seasons. At the same time, the maximum values of snow cover extent reduction rate in Eurasia are inherent in transitional seasons – autumn and spring.

Due to the increase in CO₂ content in the Earth’s atmosphere, which is highly dependent on anthropogenic emissions of CO₂, quality of emission estimation should be improved. Advanced experiment-based methods of the CO₂ anthropogenic emission estimation are built on solution of an inverse problem using highly-accurate measurements of CO₂ content and numerical models of transport and chemistry in the atmosphere. The accuracy of such models greatly determines errors of the emission estimations. In a current study temporal variations of column-average CO₂ content in an atmospheric layer from surface to the height of ~70–75 km (XCO₂) in the Russian megapolis of St. Petersburg during Jan 2019–Mar 2020 simulated by WRF-Chem model and measured by IR Fourier-transform spectrometer Bruker EM27/SUN are compared. The research has demonstrated that the WRF-Chem model simulates well the observed temporal variation of XCO₂ in the area of St. Petersburg (correlation coefficient of ~0.95). However, using CarbonTracker v2022-1 data as chemical boundary conditions, the model overestimates XCO₂ relative to the observations significantly during almost the whole period of investigation – systematic difference and standard deviation of the difference are 4.2 and 1.9 ppm (1 and 0.5%). A correction of the chemical boundary conditions which is based on analysis of a relation between near-surface wind direction and XCO₂ variation notably decreases the systematic difference between the modelled and observed data (almost by a factor of 2). The XCO₂ variation by the observations and modelling with uncorrected chemical boundary conditions are in a better agreement during vegetation season. Probably this is related to the compensation of the systematic difference by inaccuracies in estimated biogenic contribution. Hence, the reason of the still existing mean difference between the modelled and observed data can be inaccuracies in setting chemical boundary conditions for upper troposphere and in estimating how biosphere influences CO₂ content.

The problem of constructing asymptotics of the far wave fields that arise at the interface between ice and an infinitely deep liquid in the flow around a localized source is solved. An integral representation of the solution is obtained, and an asymptotic representation of the solution for supercritical modes of wave generation is constructed using the stationary phase method. The exact and asymptotic results are compared, and it is shown that the asymptotics far from the source make it possible to describe the amplitude-phase structure of far wave fields.