Vol 64, No 4 (2024)

Flare ribbons formed in solar two-ribbon flares after eruptions of prominences diverge in opposite directions from the polarity inversion line of the photospheric longitudinal magnetic field, sharply slowing down with time and distance from this line. Examples of such events are given and the kinematics of flare ribbons is demonstrated. A comparison of the position of the ribbons with the distribution of the photospheric magnetic field shows that the separation of the ribbons slows down when they enter a region of a strong longitudinal field. A simple model of prominence eruption illustrates the kinematic features of the motion of the ribbons and the relation to the sources of the coronal magnetic field in the photosphere.

The variation of the carrier frequency of serpentine emission f_SE observed in the frequency range 0.1 – 5.0 Hz under conditions of a quiet magnetosphere (Kp ~ 0 – 2) was studied. The data of magnetic field registration at the Antarctic Vostok Observatory (corrected geomagnetic coordinates F'=−85.41°, L'=69.01°) for the 1970‒1972 were used in an analysis. The 90 cases of serpentine emission observation, the central carrier frequency of which smoothly decreased (several times, sometimes to 0) and then increased almost to the initial level at time intervals significantly exceeding the maximum modulation period (1 hour) were analyzed using dynamic spectra of ULF emission. In this case, the typical modulation of the emission carrier frequency with periods of 1 – 60 min was persisted. The most likely time of observation of the detected effect was in the hours before midnight. It is shown that a decrease of the f_SE and its subsequent increase were observed against the background of weak geomagnetic activity and relative stability of the dominant number of solar wind and IMF parameters. Taking into account the discovered synchronous coincidence of the behavior of the f_SE and the dynamics of the AE index, as well as the observation of the effect of a decrease in the carrier frequency near local midnight, it is assumed that serpentine emission is most likely excited near the polar cusp and then penetrates into the region of the polar cap. The behavior of f_SE observed over long time intervals is presumably controlled by the plasma parameter β and the ratio of the proton density to the density of helium ions Np/Na, the dynamics of which are similar to the average variation of f_SE.

Based on data from mid-latitude ionospheric stations at close corrected geomagnetic latitudes, the properties of the variability in the F2 layer peak density (NmF2) at different longitudes were analyzed during increased (48 > ap(t) > 27) and high (ap(t) > 48) geomagnetic activity, where ap(t) is the weighted average ap-index of this activity. The standard deviation s of Nm fluctuations with respect to the quiet level and the average shift of these fluctuations x_ave were used as characteristics of this variability. It was found that at all analyzed stations, the variance s² for increased geomagnetic activity is greater than for quiet conditions but hardly differs from s² for high geomagnetic activity. For all analyzed cases, the average shift x_ave < 0, and for high geomagnetic activity, the absolute value of x_ave is greater than for increased geomagnetic activity. The difference in x_ave values between the analyzed stations is quite large. One reason for this difference may be related to the dependence of x_ave on geomagnetic latitudes. Approximations of the geomagnetic field by the tilted dipole (TD), eccentric dipole (ED), or using corrected geomagnetic (CGM) coordinates were used to select these latitudes. It was found that the dependence of x_ave on ED latitude is more accurate than the dependence of x_ave on TD latitude and, moreover, the dependence of x_ave on CGM latitude. Therefore, ED latitudes, and not CGM latitudes, are optimal for accounting for storm effects on the F2 layer peak density at mid-latitudes. This conclusion has apparently been obtained for the first time.

The influence of the meteorological storm in October 2018 in the Baltic Sea on the state of the mesosphere and lower thermosphere is investigated. The wave activity of gravity waves was analyzed using TIMED/SABER satellite data and the effects of the meteorological storm at altitudes of 80-100 km were determined. A method based on mode decomposition from SABER data was adapted to calculate the gravity waves potential energy density and to separate the temperature perturbations due to their propagation at lower thermospheric heights. The wavelet analysis of temperature perturbations revealed two ranges of vertical wavelengths 5-8 km and 14-18 km. In the area of a meteorological storm, the GWs amplitude with vertical wavelengths of 5-8 km increases, and the area of their maximum expands and shifts upward to heights of ~90 km, while on meteorologically calm days these waves are observed at heights of 65-70 km and with smaller amplitudes. Above the meteorological storm region at altitudes of 90-100 km, the values of the gravity waves potential energy density significantly increase compared to calm days before and after the storm, as well as the spatial dimensions of the disturbance region increase.

For a number of events, the propagation velocities of geomagnetic Pc5 pulsations in the azimuthal and meridional directions were analyzed. Two methods were used: by the phase delays of the signal between stations and by the displacement of the vortex centers of their equivalent current systems. The analysis showed that the distribution of pulsations and vortices coincides in direction: along the meridian they predominantly propagate to the north. In most cases, the propagation velocity of pulsations is 5 km/s, and that of vortices is 2 km/s. In azimuth, pulsations and vortices propagate westward, the propagation velocity of pulsations is 10 km/s, and the vortices velocity is 3 km/s. However, in the distribution of azimuthal velocities of both pulsations and vortices there are maxima of comparable magnitude, corresponding to the eastward propagation: pulsations with a velocity of 10 km/s, and vortices with a velocity of 5 km/s. It is concluded that at the ionospheric level, the phase velocities of pulsations measured by us are approximately 2 times greater than the group velocities of the vortices.

The study of the deep structure and tectonics of the Arctic region is actual both for the modern geodynamics fundamental problems solving and for the natural resources developing in the Polar Regions, besides it is of interest from a geopolitical perspective in determining the boundaries of the marginal seas shelve.

To analyze the anomaly magnetic field in the Polar Arctic region CHAMP satellite experimental data obtained at the last stage of its mission, when its orbit altitude dropped to 280–260 km, were used. The reduced height of passes made it possible to obtain geomagnetic parameters with a higher spatial resolution. The maps of the lithospheric magnetic anomalies field lateral distribution have been constructed for the various scales and degrees of space averaging over the discussed Arctic sectors. The analysis of the magnetic anomaly parameters is carried out and an explanation of their geological and physical nature is proposed supposing they are the images of the most significant geological and tectonic structures of the North Atlantic Igneous Province and of the Central Arctic ridges complex.

The connections of the discovered features of the lithospheric magnetic anomaly field distribution with the known geological structures of Amerasia and Eurasia and the tectonic processes that took place here in the past and are currently taking place are discussed. The obtained results could be useful for further comprehensive geological and geophysical studies and for construction of the reasonable lithosphere evolution models of the Arctic region.