Vol 61, No 2 (2025)

An analysis of the influence of boundary conditions on the instability of a geostrophic zonal current of finite transverse scale with a vertical parabolic velocity profile of a general form in a vertically limited layer has been carried out. The model is based on the potential vortex equation in the quasi-geostrophic approximation, taking into account the vertical diffusion of mass and momentum. The equation and boundary conditions were reduced to a spectral eigenvalue problem of the Orr–Sommerfeld type. A high-precision analytical-numerical method was used to calculate eigenfunctions and eigenvalues. Two types of conditions at the horizontal boundaries of the layer were considered: the equality of vertical velocity disturbances and buoyancy fluxes to zero (problem I); equality of vertical velocity disturbances and horizontal velocity disturbances to zero (problem II). It is found that the boundary conditions of problem II, which include no-slip conditions, contribute to the stabilization of long-wave unstable disturbances and narrow the range of unstable short-wave disturbances. It is noted, however, that all types of current instability obtained by solving problem I, such as baroclinic instability, instability of the critical layer, as well as new instability, characterized by a phase velocity exceeding the maximum current velocity, also arise when using no-slip boundary conditions, but in a narrower range of changes in the physical parameters of the original equation.

Long-term trends in the North Atlantic Ocean (0°–70°N, 8°–80°W) salinity are estimated from several ocean reanalyses and objective analyses over the period 1980–2011. The obtained estimates are based on the application of a nonparametric method of regression analysis (quantile regression) to the monthly ocean salinity for a quantile value of 0.5. During the period under consideration, in the latitude band 0°–15° N in the 10–50 m layer, salinity decreased by 0.17 ± 0.10 PSU. In the latitude band 20°–35° N the increase in salinity in the 10–400 m layer is 0.08 ± 0.03 PSU. In the eastern part of the Subtropical Atlantic (30°–40° N, 25°–45° W), significant salinization of the upper 400 m layer occurs in all months. This means a northwestward expansion of the high salinity region in the subtropics. In the western part of the subpolar gyre, salinity in the upper 400 m layer increased by 0.20 ± 0.05 PSU over this 32-year period.

This work studies the dependence of the amplitude of the diurnal cycle of the Azov-Black Sea basin surface temperature on a number of hydrometeorological factors and its seasonal variability using SEVIRI radiometer data and modeling of the upper mixed layer of the sea. According to remote sensing data, the minimum amplitude values occur in the cold season when the full heat flux is directed into the atmosphere, winds are strong and air temperatures are low. The maximum amplitudes occur during the warm season, when the full heat flux is directed to the sea, the air temperature is the highest, and there is almost no wind. The work also provides the calculations using the Kraus–Turner model with a special choice of atmospheric influence parameters. The obtained model results are in good agreement with the results of research of the diurnal cycle amplitude according to the SEVIRI scanner data. Model calculations made it possible to identify the variability of the thickness of the upper-ocean mixed layer while taking into account the variability of the parameters of atmospheric influence – heat flux and wind speed.

The paper assesses anthropogenic emissions and absorptions of greenhouse gases from energy reservoirs in the Russian Federation based on the results of field measurements in 2021–2023. Measurements of methane fluxes from the surface of reservoirs were carried out by employees of the Institute of Atmospheric Physics of the Russian Academy of Sciences in the shallow and deep-water parts of the basins of nine reservoirs (Kolymskoye, Bureiskoye, Volgogradskoye, Boguchanskoye, Zeyskoye, Kuibyshevskoye, Rybinskoe, Chirkeyskoe, Sayano-Shushenskoe). Based on these measurements and modeling data, we analyzed and compared the obtained results with the methane emission factors presented in the methodological documents of the Intergovernmental Panel on Climate Change (IPCC). We have developed adjusted coefficients using Tiers 1 and 2 methods according to the IPCC. The results show that the revised national factors are on average 63% lower than the default IPCC factors. A methodology for assessing the anthropogenic component of the greenhouse gas balance due to reservoir construction using Tier 3 method has been developed based on carbon balance calculations and the difference between the parameters of the reservoir water and the river before it. Using the example of the Rybinsk Reservoir, we assessed the anthropogenic component of the greenhouse gas flow, corresponding to a net absorption of 0.18 kg CO₂-eq/m²/year. A conclusion has been made about the possibility of a negative carbon footprint of electricity from large hydroelectric power plants.