We present unusual negative magnetic bay-like disturbances occurred in the dayside polar geomagnetic latitudes under positive IMF Bz. The considered events were observed during the recovery phase of the storm of May 30, 2003 and the main phase of the storm of Nov 24, 2001. We call such magnetic disturbances “dayside polar substorms”. It is supposed that the development of dayside polar substorms can be represented as a magnetospheric response to a significant change of the IMF Bz from negative to high positive values. The vector construction of the geomagnetic data (Scandinavian magnetometer chain IMAGE) demonstrated a clockwise vortex during the storm of Nov 24, 2001, and two opposing vortices in the event of May 30, 2003. These vortices could be regarded as a proxy of an intensification of downward and upward field-aligned currents. This assumption is based on the IZMIRAN model estimations and the simultaneous DMSP and CHAMP satellite data. According to the OVATION model and the electron images from IMAGE satellite, the Scandinavian polar stations that registered these dayside polar magnetic substorms, were mapped into the dayside auroral oval, i.e. inside the closed magnetosphere. © 2017 BBSCS RN SWS. All rights reserved

The high-latitude geomagnetic effects of an unusually long initial phase of the largest magnetic storm ( SymH ~–220 nT) in cycle 24 of the solar activity are considered. Three interplanetary shocks characterized by considerable solar wind density jumps (up to 50–60 cm –3 ) at a low solar wind velocity (350–400 km/s) approached the Earth’s magnetosphere during the storm initial phase. The first two dynamic impacts did not result in the development of a magnetic storm, since the IMF Bz remained positive for a long time after these shocks, but they caused daytime polar substorms (magnetic bays) near the boundary between the closed and open magnetosphere. The magnetic field vector diagrams at high latitudes and the behaviour of high-latitude long-period geomagnetic pulsations ( ipcl and vlp ) made it possible to specify the dynamics of this boundary position. The spatiotemporal features of daytime polar substorms (the dayside polar electrojet, PE ) caused by sudden changes in the solar wind dynamic pressure are discussed in detail, and the singularities of ionospheric convection in the polar cap are considered. It has been shown that the main phase of this two-stage storm started rapidly developing only when the third most intense shock approached the Earth against a background of large negative IMF Bz values (to–39 nT). It was concluded that the dynamics of convective vortices and the related restructing of the field-aligned currents can result in spatiotemporal fluctuations in the closing ionospheric currents that are registered on the Earth’s surface as bay-like magnetic disturbances.

Features of high-latitude geomagnetic disturbances during the magnetic storm (Dst min =–144 nT) recovery phase were studied based on the observations on the Scandinavian profile of magnetometers (IMAGE). Certain non-typical effects that occur under the conditions of large positive IMF Bz values (about +20–25 nT) and large negative IMF By values (to–20 nT) were revealed. Thus, an intense (about 400 nT) negative bay in the X component of the magnetic field (the polar electrojet, PE) was observed in the dayside sector at geomagnetic latitudes higher than 70°. As the IMF B y reverses its sign from negative to positive, the bay in the X component was replaced by the bay in the Y component. The possible distribution of the fieldaligned currents of the NBZ system was analyzed based on the CHAMP satellite data. The results were compared with the position of the auroral oval (the OVATION model) and the ion and electron flux observations on the DMSP satellite. Analysis of the particle spectra indicated that these spectra correspond to the auroral oval dayside sector crossings by the satellite, i.e., to the dayside projection of the plasma ring surrounding the Earth. Arguments are presented for the assumption that the discussed dayside electrojet (PE) is localized near the polar edge of the dayside auroral oval in a the closed magnetosphere. The features of the spectral and spatial dynamics of intense Pc5 geomagnetic pulsations were studied in this time interval. It was established that the spectrum of high-latitude (higher than ~70°) pulsations does not coincide with the spectrum of fluctuations in the solar wind and IMF. It was shown that Pc5 geomagnetic pulsations can be considered as resonance oscillations at latitudes lower than 70° and apparently reflect fluctuations in turbulent sheets adjacent to the magnetopause (the low-latitude boundary layer, a cusp throat) or in a turbulent magnetosheath at higher latitudes.

The work to establishment of features generation of magnetic substorms interplanetary magnetic clouds, with participation in this process its sheathes is devoted. Research based on comparison parameter dynamics of magnetic clouds fine structure and clouds sheath with dynamics of auroral AL-index and Dst-index of global geomagnetic activity. Clouds sheath is original source of high-latitude activity and gives start to global magnetic storms. Storm development provided by body magnetic cloud parameters was found. However, separate sheath clouds rarely causes global geomagnetic activity, causing usually weak or moderate geomagnetic storms. The most often source of global disturbances becomes a combination of sheath and body, causing classical strong or multi-step storm.

The high-latitude geomagnetic events that occurred under extreme space weather conditions during the non-typical development of the main phase of the strong magnetic storm of November 24, 2001 were studied. The development of the main phase was or ceased by a sharp turn of the IMF to the north and the appearance of extremely high (up to about 60 nT) positive IMF Bz values; in this period, high alternating IMF By values were observed (from +40 to −40 nT) against a high dynamic pressure of the solar wind, with sharp bursts up to 50–70 nPa. This resulted in the cessation of nighttime substorms. Magnetic disturbances were recorded on the Earth’s surface only in the daytime sector of polar latitudes as a very strong magnetic bay with amplitude of about 2000 nT. According to model calculations, a sharp intensification of field-aligned currents of the NBZ system was noted in that region. The onset of the daytime polar magnetic bay was accompanied by an auroral burst and strong local geomagnetic pulsations in the ∼(2–7) mHz band. Bursts of fluctuations in the solar wind and IMF were not accompanied by simultaneous bursts in ground based high-latitude geomagnetic pulsations, that is, the direct penetration of solar wind and IMF pulsations into the magnetosphere was unlikely to occur. The daytime polar geomagnetic pulsations observed on the Earth’s surface could be caused by variations in high-latitude field-aligned currents, which were excited in a turbulent daytime boundary layer as a result of interaction with solar wind inhomogeneities.

Представлены результаты модельного расчета магнитного возмущения, зафиксированного в обсерватории Колаба (Индия) в период исторической гигантской магнитной бури 1–2 сентября 1859 года. Расчет демонстрирует возможность генерации наблюдаемой необычайно быстрой двухчасовой главной фазы этой бури с отрицательной амплитудой H-компоненты вектора геомагнитного поля –1600 нТл и необычайно быстрой полуторачасовой начальной фазой восстановления поля от максимума до амплитуды –110 нТл. При расчете использовались модели магнитосферных токовых систем: кольцевой ток (DR), ток на магнитопаузе магнитосферы (DCF), токовая система хвоста магнитосферы (DT) и высокоширотная токовая система (DP). Природа необычной временной динамики зарегистрированного геомагнитного возмущения связана с возможным быстрым и значительным по величине смещением высокоширотных токов в сторону экватора во время главной фазы анализируемой гигантской бури и таким же быстрым перемещением их обратно на начальной фазе восстановления поля. Необычайно большая амплитуда зафиксированного геомагнитного возмущения могла быть вызвана суммарным вкладом указанных магнитосферных токовых систем в период генерации бури в результате взаимодействия магнитосферы с веществом солнечного плазменного выброса во время гигантской солнечной вспышки, предшествующей буре.

The model calculation of a magnetic disturbance, which was registered at Colaba observatory (India) during the historic giant magnetic storm on September 1–2, 1859, is illustrated. The calculation demonstrates that the observed, unusually fast, 2-h main phase of this storm, when the negative amplitude of the geomagnetic field vector H component was −1600 nT, and an extremely fast (1.5-h) initial field recovery phase from the maximum to the −110 nT amplitude can be generated. The following models of the magnetospheric current systems were used in the calculations: the ring current ( DR ), the magnetospheric magnetopause current ( DCF ), the magnetotail current system ( DT ), and the high-latitude current system ( DP ). The unusual time variation in the registered geomagnetic disturbance is related to the probable fast and considerable equatorward shift of the high-latitude currents during the main phase of the analyzed giant storm and to the same fast backward motion of these currents during the initial field recovery phase. The unusually large amplitude of the registered geomagnetic disturbance could have been caused by the total contribution of the indicated magnetospheric current systems during the time when the storm was generated as a result of the interaction between the magnetosphere and the solar plasma ejected during the gigantic solar flare before the storm.

Выполнена классификация комплексов космической погоды, включающих в себя характеристики солнечных потоков (параметры солнечного ветра, компоненты вектора межпланетного магнитного поля) и временные количественные оценки их геомагнитных проявлений (Dst-индекс). Разработаны сопоставительный и нейросетевой методы такой классификации. В результате численных нейросетевых экспериментов установлены типы солнечных потоков, отвечающие за генерацию геомагнитных возмущений разной интенсивности. Подтверждено, что, на основе выделенных комплексов космической погоды, возможно уточнение влияния этих потоков на электромагнитное состояние магнитосферы, и, соответственно, повышение точности прогнозирования этого состояния.

Method of short-term forecast intensity of geomagnetic storms, expected by effect Solar wind magnetic clouds in the Earth’s magnetosphere is developed. The method is based calculation of the magnetic field clouds distribution, suitable to the Earth, the initial satellite measurements therein components of the interplanetary magnetic field in the solar ecliptic coordinate system. Conclusion about the magnetic storm intensity is expected on the basis of analysis of the dynamics of the reduced magnetic field Bz component clouds and established communication intensity of geomagnetic storms on Dst-index values and Bz component of the interplanetary magnetic field vector.

A new method for determining geomagnetic activity based on calculation of the hourly amplitudes of geomagnetic field variations at ground-based observatories has been developed. Observations performed in 2009, when unusually low solar and geomagnetic activity was registered, were used as a reference level. The described method was used to estimate the energy of local geomagnetic activity; such energy is estimated for observatories in the Earth's Northern and Southern hemispheres, and a total estimation is made for both hemispheres and for the entire Earth's surface during large magnetic storms. These are used to compare characteristics of magnetic storm intensity based on the classical Kp and Dst indices and calculated energy estimate.

The space-weather complexes including characteristics of solar streams (parameters of the solar wind, components of the interplanetary magnetic-field vector) and temporal quantitative estimates of their geomagnetic effects (Dst index) are classified. Comparative and neural-network methods for this classification are developed. As a result of numerical neural-network experiments, types of solar streams responsible for generation of geomagnetic perturbations with different intensities are established. It is confirmed that, on the basis of the selected space weather complexes, it is possible to refine the influence of these streams on the electromagnetic state of the magnetic sphere and, hence, improve the accuracy of predictions of this state.

Measurements onboard Cluster satellites are briefly described, which form the base for determining the intensity and direction of the electric field in the magnetosphere. The aim of this paper is to describe (1) the methodology of calculating the potential distribution at the ionospheric level and the results of constructing spatiotemporal convection patterns for different orientations of the IMF vector in the GSM YZ plane; (2) derivation of basic convection patterns (BCPs), which allow to deduce the statistical ionospheric convection pattern at high latitudes for any IMF Bz and By values (statistical convection model) using different sets of independent data; (3) the consequences of enlarging the amount of data used for analysis; (4) the results of potential calculations with various orders of the spherical harmonics describing them; (5) determination of the cross-polar cap potential with different IMF sector widths (α from 45° down to 10°); (6) the results of our trials to determine the contribution of the IMF Bx component to the convection pattern.

The conception of spiral shaped precipitation regions, where solar corpuscles penetrate the upper atmosphere, was introduced into geophysics by C. Störmer and K. Birkeland at the beginning of the last century. Later, in the course of the XX-th century, spiral distributions were disclosed and studied in various geophysical phenomena. Most attention was devoted to spiral shapes in the analysis of regularities pertaining to the geomagnetic activity and auroras. We review the historical succession of perceptions about the number and positions of spiral shapes, that characterize the spatial-temporal distribution of magnetic disturbances. We describe the processes in the upper atmosphere, which are responsible for the appearance of spiral patterns. We considered the zones of maximal aurora frequency and of maximal particle precipitation intensity, as offered in the literature, in their connection with the spirals. We discuss the current system model, that is closely related to the spirals and that appears to be the source for geomagnetic field variations during magnetospheric substorms and storms. The currents in ionosphere and magnetosphere constitute together with field-aligned (along the geomagnetic field lines) currents (FACs) a common 3-D current system. At ionospheric heights, the westward and eastward electrojets represent characteristic elements of the current system. The westward electrojet covers the longitudinal range from the morning to the evening hours, while the eastward electrojet ranges from afternoon to near-midnight hours. The polar electrojet is positioned in the dayside sector at cusp latitudes. All these electrojets map along the magnetic field lines to certain plasma structures in the near-Earth space. The first spiral distribution of auroras was found based on observations in Antarctica for the nighttime-evening sector (N-spiral), and later in the nighttime-evening (N-spiral) and morning (M-spiral) sectors both in the Northern and Southern Hemispheres. The N- and M-spirals drawn in polar coordinates form an oval, along which one observes most often auroras in the zenith together with a westward electrojet. The nature of spiral distributions in geomagnetic field variations was unabmibuously interpreted after the discovery of the spiral's existence in the auroras had been established and this caused a change from the paradigm of the auroral zone to the paradigm of the auroral oval. Zenith forms of auroras are found within the boundaries of the auroral oval. The oval is therefore the region of most frequent precipitations of corpuscular fluxes with auroral energy, where anomalous geophysical phenomena occur most often and with maximum intensity. S. Chapman and L. Harang identified the existence of a discontinuity at auroral zone latitudes (Φ ∼ 67°) around midnight between the westward and eastward electrojets, that is now known as the Harang discontinuity. After the discovery of the auroral oval and the position of the westward electrojet along the oval, it turned out, that there is no discontinuity at a fixed latitude between the opposite electrojets, but rather a gap, the latitude of which varies smoothly between Φ ∼ 67° at midnight and Φ ∼ 73° at 20:00 MLT. In this respect the term ''Harang discontinuity'' represents no intrinsic phenomenon, because the westward electrojet does not experience any disruption in the midnight sector but continues without breaks from dawn to dusk hours.