Vol 54, No 5 (2018)

A thorough investigation of short-period oscillations in the Earth’s magnetic field as a fundamental natural process of the magnetospheric plasma began in Russia after V.A. Troitskaya established two oscillatory regimes in the geomagnetic field, namely, the regimes of continuous (Pc) and irregular pulsations (Pi). For studying these pulsations, 19 stations recording the telluric currents were installed during the International Geophysical Year (IGY, 1957–1959) on Troitskaya’s initiative. One of these stations was the Borok station. Subsequently, Borok has become the basic site for investigating geomagnetic pulsations and the main center for studying the short-period pulsations (SPPs) in the Earth’s magnetic field. This is the Borok scientific station where the key fundamental regularities of different types of geomagnetic pulsations were established. Troitskaya led and actively participated these works. Troitskaya organized and conducted the first complex geomagnetic observations in the world at the conjugate points Sogra (Arkhangelsk region, Russia) and Kerguelen (Indian Ocean). These studies were initially tested at the Borok observatory, where it was established that the wave packets of Pc1 geomagnetic pulsations are alternately observed in the northern and southern hemispheres in contrast to the other pulsation types which simultaneously occur in both hemispheres. The studies carried out at Borok promoted the establishment of a new direction in geophysics—diagnostics of the state of the magnetosphere based on the ground observations of geomagnetic pulsations. The analysis of simultaneous observations of the geomagnetic pulsations at polar latitudes of the Arctic and Antarctic was also for the first time conducted at the Borok observatory. This analysis revealed the main characteristics of wave phenomena at the geomagnetic poles and in the vicinity of the projection of the dayside polar cusp. Thus, for the first time in the world, Troitskaya and her Borok colleagues established the key patterns of the oscillatory regimes in the geomagnetic field of the Earth. This laid the basis for the further experimental and theoretical investigations which have shown that SPPs play a leading role in the dynamics of the magnetospheric plasma. In this paper we also list of 60 of Troitskaya’s main publications.

Based on the data from the Vostok station, Antarctica, for the period from 1966 to 1971, the frequency modulation of the serpentine-emission-type (SE) geomagnetic pulsations is studied. The spectral analysis of the selected emission events revealed a number of modulation periods in the interval from 1 to 60 min. The 5-min SE modulation period is most common. The obtained results are compared to the observations of solar atmosphere oscillations. The correspondence of the periods of the SE frequency modulation to the periods of oscillations of the solar photosphere is established. This confirms the previously suggested hypothesis of the existence of a genetic connection between the frequency modulation of the emission and oscillations of the solar surface.

Polarization characteristics (polarization type, ellipticity ε, tilt angle τ of the polarization ellipse’s major axis) of high-latitude magnetic impulse events (MIEs) observed at the latitude of the dayside polar cusp are studied. It is established that all impulses are elliptically polarized, being right-polarized in 43% of cases (R-type) and left-polarized in 57% of cases (L-type). The right-polarized MIEs on the ground are more pronounced in the azimuthal direction, whereas the left-polarized events are more clearly marked in the meridional direction. The MIEs of both polarization types have the properties of intermittent processes. It is shown that diurnal and seasonal variations in the occurrence frequency and amplitudes of the events depend significantly on the type of their polarization. The R- and L-type impulse events are predominantly observed during the descending and ascending phase of the solar cycle, respectively. Solar wind high-speed streams (HSSs) are more favorable for exciting right-polarized impulses, whereas left-polarized impulse events are more efficiently excited by coronal mass ejection (CME). It is established that R-type impulses emerge in the conditions when the orientation of the interplanetary magnetic field vector is close to the radial direction against the development of moderate magnetospheric substorms whereas the L-type impulses appear when IMF is perpendicular to the Sun–Earth line in the absence of substorms. The behavior of the characteristics of impulse events significantly depends on the value of the IMF Bz-component and on the angle θ_xB = arccos(Bx/B). It is conjectured that excitation of the two groups of impulses is caused by the IMF structures in the solar wind stream with the characteristic configuration in the ecliptic plane, which determine the polarization type and properties of MIEs.

The propagation of perturbation caused by the interplanetary shock wave of March 17, 2015 from the solar wind through the magnetosheath, magnetosphere, and ionosphere down to the Earth’s surface is analyzed. The onboard satellite measurements, global magnetometer network data, and records by the receivers of the global positioning system (GPS) providing the information about the total electron content (TEC) of the ionosphere are used for the analysis. By the example of this event, various aspects of the influence of the interplanetary shock wave on the near-Earth environment and ground-based engineering systems are considered. It is shown which effects of this influence are well described by the existing theoretical models and which ones need additional research. The formation of the fine structure of the magnetic impulse of the storm sudden commencement (SC)—the preliminary impulse (PI) and main impulse (MI)—is considered. The MI and compression of the magnetospheric magnetic field is observed by the GOES and RBSP satellites and on the geomagnetically conjugate stations; however, the PI was only noted on the Earth. The PI was detected in the afternoon sector practically simultaneously (within 1 min) with the shock wave impact on the magnetopause. The wave’s response to the SC includes the strongly decaying resonant oscillations of the magnetic shells and the magnetoacoustic cavity mode. This study supports the possibility of detecting the ionospheric response to the SC by the GPS method. The TEC response to the MI was detected in the auroral latitudes although not on every radio path. The TEC modulation can be associated with the precipitation of superthermal electrons into the lower ionosphere which is undetectable by riometers. The burst in the intensity of the geomagnetically induced currents caused by an interplanetary shock wave turns out to be higher than the currents during the storm’s commencement, although the SC’s amplitude is noticeably lower than the amplitude of the magnetic bay related to the substorm.

The problem of estimating the time derivatives of the horizontal components of the geomagnetic field and forecasting the probability of the occurrence of perturbations that exceed a given threshold level (the over-threshold perturbations) arises in the applications concerned with the geomagnetically induced currents (GICs). In this work, we consider the temporal and spatial structure of the Pi3 pulsations with quasi-periods of 10² to 10³ s during which the auroral and subauroral stations of the IMAGE network record over-threshold values in the derivatives of the meridional (along the longitudinal circle) B_X component and latitudinal (along the latitudinal circle) B_Y component. The extreme |dB_X/dt| values mainly develop against the background of the Pi3 pulsations with a complex frequency content, whereas the extreme |dB_Y/dt| values appear when the buildup (decay) phases of the bay-like disturbance associated with the evolution of a substorm coincide with the respective phases of the field of pulsations. The conditions under which the derivatives |dB_X/dt| and |dB_Y/dt| reach their over-threshold values are studied for subauroral latitudes by the technique of superposed epoch analysis. The extreme values of the derivatives most frequently occur during the main phase of moderate magnetic storms or beyond the storm—during high substorm activity under the conditions of a negative vertical component of the interplanetary magnetic field. The probability of the occurrence of over-threshold values increases at high amplitudes of the Pi3 pulsations and depends on their spectral content. The problem of analyzing and forecasting the over-threshold |dB_Y/dt| perturbations is complicated by the fact that the scale of the perturbations is small along the lines of latitude and large along the meridians. This can result in GIC excitation in the North–South oriented electric power lines by the geomagnetic perturbations localized within a narrow band in longitude which can be missed during the measurements.

Radon-222 is inert radioactive gas with a half-life period of 3.8 days, it is a decay product of radium-226. Being escaped from minerals and underground waters into pore space of rocks and soil, it is transported to the surface by diffusion and advection and gone to the atmosphere. When modeling processes of atmosphere radon transport one sets value of radon flux from the surface, depending on contents of radium-226 in rocks and conditions of radon transport in soil, especially on soil porosity and humidity. The impact of radon turbulent transport in the atmospheric boundary layer (ABL) on radon flux density from the surface is estimated in this paper. It is shown that both for stationary state and for typical diurnal variations of the radon volumetric activity (VA) in the ABL, the correction to the radon flux density caused by its turbulent transport in the ABL is negligible (less than 1%) and doesn’t exceed measurement errors. Thus, when calculating radon VA in the ABL it is really possible to set an average value of the radon flux density on the surface as a boundary condition.