Geomagnetizm i aèronomiâ

Solar flare of May 11, 2012 was observed on two spectrographs of the Astronomical Institute of the Czech Academy of Sciences – a multichannel flare spectrograph and a horizontal setup for solar research. After processing the spectra, integral emission fluxes in the hydrogen, helium and calcium lines were determined. Within the framework of the heated gas model, a theoretical calculation of the plasma parameters was performed taking into account the physical conditions in the chromosphere, including self-absorption in the spectral lines. A comparison of six lines at once made it possible to reconstruct the temperature, density and spatial structure of the emitting gas with a high degree of confidence. At the same time, a search for quasi-periodic pulsations in this solar flare was carried out, which showed the absence of such in almost all spectral ranges. An exception is the detection of pulsations in the images of the chromosphere on the spectrograph slit in the Hα line with a period of 30 s.

The difference in the shape of the maxima of galactic cosmic rays (GCR) fluxes for positive (A > 0, even–odd cycle minima) and negative (A < 0, odd–even cycle minima) polarities of the solar dipole magnetic field is well known. For A > 0, a flat GCR maximum is observed, while for A < 0, a sharp one. This difference is associated with the influence of the drift mechanism of GCR propagation in the global magnetic field of the heliosphere, the proxy of which can be considered the polar (dipole) magnetic field of the Sun (B_pole). A homogeneous series of GCR data has been available since 1957, while B_pole observations have been conducted only since 1976. Using the example of odd (21^st, 23^rd and 25^th) and even (22^nd and 24^th) cycles for which B_pole and GCR observations are available, we investigate the hypothesis that changes in the B_pole value and sign determine the main trends in the development of the entire modulation cycle. Traditionally, the beginning of the 11-year cycle in the long-term GCR modulation is associated with the minimum number of sunspots R_z, but the growth of R_z does not reflect all physical processes on the Sun capable of modulating GCR in the heliosphere. We select the maximum GCR intensity at 10 GV as the beginning of the modulation cycle (zero on the time scale) and then compare the count rate of the Moscow neutron monitor, the B_pole value, and the number of sunspots (R_z) using the superposition of epochs method. With such a choice of zero, the difference in the time profiles of GCRs in even and odd cycles is clearly visible. With a decrease in the B_pole module, the GCR fluxes decrease, the convective transport mechanism prevails, and the effect of drift transport is not visible (there is no clear division into even and odd cycles). With an increase in the B_pole module, the GCR fluxes grow, the diffusion mechanism of GCR transport prevails, which is helped or hindered by the drift mechanism (at A > 0 or at A < 0). The GCR fluxes remain constant at B_pole ~ const. The spot activity R_z is asymmetrical relative to the moment of polarity reversal (B_pole = 0), it is early in even and late in odd cycles. The discovered trends allow us to qualitatively predict the corridor of possible changes in B_pole and GCR fluxes in the decline phase of the 25^th cycle and in the minimum of 25–26 cycles, as well as to make an epignostic forecast based on observations of GCR and R_z of possible B_pole values in 1957–1976 (the end of the 19^th and the entire 20^th cycle).

The results of determination of the long-term trends in the parameters of the ionospheric F2 layer (critical frequency, height, total electron content, and slab thickness) are considered. It is shown that the recent results of determination of the foF2 trends agree with the results of the detailed analysis of the data of stations in two hemispheres published by the authors. Possible causes of appearance of the negative trends in the parameters of the F2 layer at the cooling and contraction of the thermosphere due to anthropogenic effects. Currently, a decrease in the atoms-to-molecules ratio in the thermospheric gas and an increase in the rate of the ion-molecular reactions at the temperature decrease in the winter conditions are the most probable causes of appearance of the negative trends in foF2 in the winter months. A comparison of the trends in various parameters is performed and it is shown that these trends agree with each other.

The results of studies of the behavior of the main characteristics of the F region of the ionosphere during a strong long-lasting magnetic storm on February 26–28, 2023 are presented. Variations in the critical frequency of the ionospheric F2 layer foF2 (characterizing the maximum electron density) and the height of the maximum of the F2 layer of ionosphere hmF2 are analyzed based on their relative deviations from quiet conditions. In the European region, a positive pre-storm anomaly in foF2 variations and a negative anomaly after the onset of a magnetic storm have been identified. It has been established that the hmF2 height changes greatly during a magnetic storm. The dependence of the ionospheric response on the location of the ionospheric station is shown.

The article describes two cases of observation of mesospheric bores, which are prominent wave fronts observed using night airglow data recorded by all-sky cameras over the central part of Yakutia (northeastern Siberia). The purpose of the work is to study the peculiarities of propagation and formation mechanism of this phenomenon. In the first case, the manifestation of a bore in the emissions of hydroxyl OH molecules at the level of the mesopause (altitude 87 km) and the green line of atomic oxygen [OI] (altitude 97 km) is described. In the second case, a description of a bore recorded in the emission of hydroxyl OH molecules is presented. The wavelength, phase velocity of propagation, wave period, direction of propagation, time and duration of the phenomenon, are calculated. Possible sources of formation of the mesospheric bore are also discussed.

Late Pleistocene deposits of the Karadzha section have been studied. Both vector and scalar characteristics of the rocks composing it were obtained. The main paleomagnetic elements of the section have been established: the Jaramillo paleomagnetic horizon and the boundary of the Matuyama and Brunhes zones. In addition, a number of anomalous horizons (excursions) have been identified - these are Roxolans (Monot, Lachamp, etc.), Blake, Biwa I, Jamaica and Biwa III. This abundance of dated levels, along with track dates and abundant fauna, allowed a confident comparison of the studied section with the oxygen isotope scale for the last 0.8 million years.