Critical frequency foF2 as an indicator of trends in thermospheric dynamics

Variations with time during recent decades of three parameters are considered. R(foF2) is the correlation coefficient between the nighttime and daytime values of foF2 within the same day. Stable trends are found for minimal (R(foF2)(min)) and maximal (R(foF2)(max)) values of R(foF2) over the year. The foF2(day)/foF2(night) ratio demonstrates both negative and positive trends; the sign of the trend being governed by the inclination I and declination D of the magnetic field. The correlation coefficient r(h,fo) between foF2 and the 100-hPa level in the stratosphere demonstrates a decrease (both, for the years of maximum and minimum solar activity) from the 1980s to the 1990s. The trends in all three groups of data are considered in the scope of an assumption that there is a long-term change in the circulation in the upper atmosphere. The data considered in the paper provide an indirect confirmation of the existence of this change and show the possibility that further studies of the thermospheric dynamics can be undertaken using ground-based ionospheric observations.     

Behavior of parameters of the ionospheric F2 layer at the turn of the Centuries: 1. critical frequency

The available massifs of experimental data on the critical frequency of the ionospheric F2 layer, foF2, covering the first decade of the new century, are considered. On the basis of studying these massifs, a conclusion is drawn that the scatter of foF2 values (measured by the standard deviation (SD)) relative to the dependence on solar activity has grown substantially over recent decades as compared to the period 1958–1979. The possible causes of the SD increase are considered. It is shown that the foF2 values for the period 1998–2010 decreased as compared to the period 1958–1979 by an average of 0.6 MHz which gives an estimate of the foF2 trend of ～-0.03 MHz per year. Linear trends in foF2 for some ionospheric stations are analyzed. It is obtained that, in spite of the scatter in the data, it is possible to obtain statistically significant trends for each considered situation (day and postsunset period in summer and winter). At the same time, the winter negative trends (～-0.052 MHz per year) are approximately a factor of 2 higher than the summer ones (～-0.024 MHz per year). Comparisons with the trends obtained for earlier periods show that the negative trend in foF2 increased substantially towards the first decade of our century.     

Relation between changes in foF2 and hmF2 within various time intervals

The relation between the critical frequency foF2 and F2-layer height hmF2 is considered for ten ionospheric stations in the periods before and after 1980. It is shown that in the earlier period the relation between foF2 and hmF2 is well pronounced. In the later period, a distortion of this relation is observed. The statistical characteristics of the foF2 dependence on hmF2 are spoiled. That shows that due to the cooling and contraction of the upper atmosphere the height distribution of the photochemical parameters governing the equilibrium concentration in the layer maximum changes. A larger contribution to this effect is evidently provided by changes in the atom-to-molecule concentrations ratio.     

Behavior of critical frequency <Emphasis Type="Italic">foF2</Emphasis> at various moments of the day: 1. Dependence on solar activity

Variation with solar activity level of the ratios of the critical frequencies of the F2 layer, foF2, is considered for various pairs of local time moments T1 and T2 for two seasons (winter and summer). It is found that, as a rule, the foF2(T1)/foF2(T2) behavior with the solar activity index F10.7 is different in winter and summer. The variations of foF2(T1)/foF2(T2) with F10.7 obtained from experimental data are considered from the viewpoint of the current theory of F2-layer formation. It is shown that the majority of observed characteristics of these variations are explained using the above-indicated theory. However, special cases of foF2(T1)/foF2(T2) behavior with solar activity are found for which there is still no physical explanation.     

Relationship between foF2 trends and geographic and geomagnetic coordinates

The possibility of presenting parameters k(foF2) and ΔfoF2 characterizing the change over time in the critical frequency of the ionospheric F2 layer in recent decades was considered. These parameters were previously obtained by the authors as functions of geographic coordinates, latitude and longitude. It was shown that there is such a possibility and the corresponding statistical significances of the obtained dependencies lie within the limits from ～90% to more than 99%. Simultaneously, the dependence of the linear trend k on magnetic coordinates D and I was studied. This dependence should manifest the relation of the trends in foF2 to dynamical processes (horizontal winds) via the vertical drift induced by them and the corresponding change in the F2-layer height.     

Analysis of accumulation conditions of minor elements in mineral waters: An example of hydrocarbonate sodic waters of the Nagutskoe mineralized groundwater field

Computer simulations of carbon dioxide leaching of Aptian–Albian sandstone at the Nagutskoe groundwater field, Caucasian Mineral Waters, are compared with laboratory experimental data obtained using a high-pressure autoclave under parameters close to conditions under which mineral waters are formed at the Nagutskoe and Essentuki fields (temperatures 20–25 and 65–70°C, carbon dioxide pressure up to 4.04 MPa). The solvents were distilled water and naturally occurring groundwaters from the Caucasian Mineral Waters (CMW) area, individual experimental runs lasted for 2 h, the starting material (rock) was crushed to 0.25 mm, and the gas phase was carbon dioxide. In most of the experiments, the solid: liquid phase (R/W) ratio was 1: 5 and was varied from 1: 10 to 1: 100 in other experiments. Our simulation results indicate that multiple-cycle (10 cycles) leaching leads to an increase in mineralization from 1.3 g/L to 4 g/L and transformation of the geochemical type of the waters from the hydrocarbonate calcic–sodic one (leaching cycle 1) to chloride–hydrocarbonate sodic (cycles 5 and later). The mineralization increased mostly because the and Na⁺ ions are transferred into solution at an insignificant increase in the Cl concentration and a practically unchanging concentrations of the sulfate, calcium, and magnesium ions. With regard for the averaged mineralogical composition of the sandstone (quartz, feldspars, mica, glauconite, magnetite, ilmenite, garnet, rutile, zircon, and tourmaline) used in our thermodynamic simulations, we arrived at the conclusion that the chemical compositions of the waters, including their minor-element compositions, are controlled by (i) the composition of the cement (clay, calcareous, siliceous, limonitic, chloritic, zeolitic, phosphate, sulfate, or mixed) of the rocks, (ii) weight percentages of minerals containing certain elements, and (iii) temperature, at a given composition of the gas phase of the simulated system (silty sandstone–rainwater–CO₂ gas phase).     

Analysis of the Large-Scale Dynamics of Surface Waters in the Southern Ocean with the Help of Lagrangian Drifters

We summarize the results of reconstruction of the monthly average surface circulation in the Southern Ocean according to the paths of autonomous drifting buoys launched in the course of the First Global Geophysical Experiment (FGGE) according to the Program of Investigation of Global Atmospheric Processes in 1978–1980. The data of numerical analysis reveal significant annual and seasonal variability in the behavior of the integral characteristics of the Antarctic Circumpolar Current, the west extension of the Agulhas Current, the zone of convergence of the Falkland and Brasil Currents, and the cyclonic gyres in the Weddell and Ross Seas. It is established that the dynamics of the large-scale surface circulation in the Southern Ocean can be described by two or three empirical orthogonal modes. In general, we observe a strong correlation between the locations of the zones with high kinetic energy of currents and the zones of bottom rise.     

Parameters of the ionospheric <Emphasis Type="Italic">F</Emphasis><Subscript>2</Subscript> layer as a source of information on trends in thermospheric dynamics

The problem of determining trends in thermospheric dynamics parameters (horizontal winds) based on analysis of trends in various combinations of ionospheric F ₂-layer parameters is formulated. The previous attempts of the authors in this direction are briefly described. It is shown that all studied parameters lead to the same result: after the “boundary date” (approximately 1980) a systematic change in these parameters (a long-term trend) is observed, this fact manifesting changes in the dynamical regime of the thermosphere because of cooling and contraction of the entire middle and upper atmosphere. The results of a search for trends in the hmF2 height for the moment (T(ss) + 2 h) are described. These trends are found higher than the hmF2 trends obtained earlier by various authors analyzing the hmF2 behavior at fixed moments of local time.