Vol 56, No 6 (2016)

Variations in the cosmic ray density during the initial phase of the Forbush effect during the first hours after the arrival of the interplanetary shock wave have been studied with the use of data on variations in the cosmic ray density with a rigidity of 10 GV obtained by the global survey method by the world network of neutron monitors in 1957‒2012. It is found that behavior of this parameter after the arrival of the shock wave demonstrates high variability. A small (~1/5 of total number), though distinct, group of Forbush effects, in which the density of the cosmic ray increases (not decreases) after the arrival of the shock wave, is defined. As a whole, the initial variation in cosmic ray density is correlated with the Forbush effect magnitude and the strength of the associated geomagnetic disturbance.

The structure and dynamics of electron fluxes of subrelativistic energies in the range 235–300 keV at L < 4 during December 3–8, 2014, are analyzed according to the RELEC instrument onboard the Vernov satellite. Sharp changes in the parameters of the solar wind and the IMF were detected on December 6, but they did not lead to a magnetic storm. However, after the event of December 6, subrelativistic electron fluxes in the inner belt and the slot region were enhanced and structured. The dynamics of electron fluxes in the local transient bursts at L ~ 1.5–1.7 is considered in detail. It is shown that these bursts are associated with the development of the cyclotron instability in the tops of magnetic flux tubes near the inner belt maximum. The electron anisotropic index is estimated in these bursts. It is shown that in the beginning these bursts are anisotropic and that they become isotropic as the decay proceeds. The most likely chain of physical mechanisms that could lead to variations in electron fluxes of the inner belt described in this paper is presented. For the first time, the topological effects in stationary distributions of the electrons of the inner belt observed at low altitudes in the South Atlantic Anomaly region are explained.

Characteristics of isolated substorms selected by variations in the 1-min values of the AL index are analyzed. The substorms were divided into several types with respect to the behavior of the Bz component of the interplanetary magnetic field (IMF) during the expansion phase. The probability of observations of substorms associated with the northward turn of the Bz component of IMF was ~19%, while the substorms taking place at Bz < 0 were observed in 53% of cases. A substantial number of events in which no substorm magnetic activity was observed in the auroral zone after a long (>30 min) period of the southward IMF and a following sharp turn of the Bz component of IMF before the north was detected. The data suggest that a northward IMF turn is neither a necessary nor sufficient condition for generating substorms. It has been shown for substorms of the both types that the average duration of the southward IMF to moment T₀ and the average intensity of the magnetic perturbation in the maximum are approximately the same and amount to ~80 min and–650 nT, respectively. However, for substorms at Bz < 0, their mean duration, including the expansive and recovery phases, is on average 30 min longer than that at a northward turn of IMF. Correlations between the loading–unloading processes in the magnetosphere in the periods of magnetospheric substorms were investigated with different functions that determine the efficiency of the energy transfer from the solar wind to the magnetosphere. It has been shown that the highest correlation coefficient (r = 0.84) is observed when the function suggested by Newell et al. (2007) is used. It has been detected that a simple function VB_S yields a high correlation coefficient (r = 0.75).

The all-sky camera data obtained in Barentsburg (Spitsbergen Archipelago) are compared with specific features of electron and ion precipitations on the DMSP F18 satellite during its flight within the camera field of view on December 15, 2012. Before arriving at the cusp from the mantle side, the satellite detects two outbursts of precipitating particles. The burst of mantle precipitations far from the cusp is observed simultaneously in both ionic and electronic components. In the ionosphere related to the satellite, no auroras are detected, which is likely due to the low intensity of the flux of precipitating electrons and their low energy (80 eV). Near the cusp, a more intensive burst of precipitations of higher-energy electrons (140 eV) is accompanied by an almost complete “locking” of ions. This burst of mantle precipitations is related to the faint luminous structure in the ionosphere. The ion locking is indicative of the accelerating potential difference in the force tube, which is based on the glowing region. The luminous structure is an element of the so-called “polewar moving auroral forms,” which is related in the literature to the reconnection in the daytime magnetopause. The possible relation of the observed phenomena to the reconnected magnetic force tubes, which drift from the cusp in the antisolar direction, is also confirmed by the dispersion of ionic precipitations, i.e., an increase in ion energy as the satellite approaches to the cusp.

A spherical plasma inhomogeneity located at mesospheric altitudes in a thundercloud quasi-electrostatic field is considered as a possible cause of sprite formation. A simple semianalytical model of ionization instability in a quasi-electrostatic field, the value of which is larger than the air breakdown value, is developed on the assumption that plasma ball conductivity is controlled by impact ionization and electron attachment to neutrals. After several simplifications, the problem is reduced to a system of ordinary differential equations for the average conductivity and plasma ball radius. The analytical estimates and numerical simulation indicate that the predicted expansion rate and acceleration of the plasma inhomogeneity boundary are close in magnitude to the values observed during high-speed imaging of sprite development.

Based on the known forecast of solar cycle 25 amplitude (Rz_max ≈ 50), the first assessments of the shape and amplitude of this cycle in the index of solar activity F10.7 (the magnitude of solar radio flux at the 10.7 cm wavelength) are given. It has been found that (F10.7)_max ≈ 115, which means that it is the lowest solar cycle ever encountered in the history of regular ionospheric measurements. For this reason, many ionospheric parameters for cycle 25, including the F2-layer peak height and critical frequency (hmF2 and foF2), will be extremely low. For example, at middle latitudes, typical foF2 values will not exceed 8–10 MHz, which makes ionospheric heating ineffective in the area of upper hybrid resonance at frequencies higher than 10 MHz. The density of the atmosphere will also be extremely low, which significantly extends the lifetime of low-orbit satellites. The probability of F-spread will be increased, especially during night hours.

The possibility of the influence of a powerful radiowave on the ozone concentration in the lower part of the ionospheric D region is discussed on the basis of experiments at the Sura heating facility in March 2009, the results of which were published relatively recently by a group of authors. The results, which were obtained with the use of exact equations of the mesospheric ozone photochemistry, substantially disagree with some conclusions derived by the authors but do not completely deny their hypothesis on the possible influence on the ozone of internal gravity waves formed at heights of the ionospheric E region.

The spectra of the anomalous geomagnetic field measured at ground and balloon (30 km) altitudes were analyzed. The ground-based data were adapted from a map of the anomalous magnetic field of the Earth. A balloon surveys was carried out by the authors. It has been shown that the ground and balloon spectra of the anomalous magnetic field of the Earth substantially differ. Suppositions explaining the differences in the obtained spectra have been suggested.