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Vol 59, No 1 (2019)
- Year: 2019
- Articles: 13
- URL: https://journals.rcsi.science/0016-7932/issue/view/9555
Article
Solar Wind Streams of Different Types and High-Latitude Substorms
Abstract
The effects of different large-scale solar wind structures on magnetospheric substorms at high geomagnetic latitudes are studied. Two types of high-latitude substorm disturbances are considered: substorms observed in quiet conditions, when the auroral oval contracts and shifts towards high latitudes (contracted oval substorms, or polar substorms), and those observed in disturbed conditions, when the auroral oval expands (expanded oval substorms, or expanded substorms). Ground-based magnetic observations from the Scandinavian IMAGE network are compared with the OMNI solar wind database and the catalog of large-scale solar wind phenomena (ftp://ftp.iki.rssi.ru/omni/). The study involves the following types of solar wind streams: (1) high-speed streams from coronal holes (FAST); (2) interplanetary manifestations of coronal mass ejections, i.e., magnetic clouds (MCs) or EJECTA; and (3) plasma compression regions ahead of these streams, i.e., corotating interaction regions (CIRs) and SHEATH. The study includes 186 polar and 202 expanded substorms in 1995, 1996, 1999, and 2000. It is shown that ~75% of expanded substorms are observed in FAST streams or plasma compression regions ahead of these streams (CIRs), and only ~18% of such substorms are observed in interplanetary manifestations of coronal mass ejections EJECTA and in SHEATH compression regions. While ~67% of polar substorms are observed in SLOW streams, ~19% of such substorms have been recorded in SHEATH and EJECTA but only against the background of a slow solar wind.
1-6
Correlation of the Radial and Meridional Components of IMF and the Solar Wind Velocity: Dependence on the Time and the Fluctuation Frequency
Abstract
The behavior of the correlation between the radial BR and normal BN components of the interplanetary magnetic field (IMF) in the dependence on the time, the flow type of the solar wind, and the frequency of fluctuations has been studied with consideration of the peculiarities in IMF sectors of different signs. Based on the data of the Wind spacecraft obtained in 1995−2011, it has been found that the correlation between BR and BN is strongest in the periods of the solar activity minima and that the annual averages of the correlation coefficient obey the rules CRN > 0 or CRN < 0 northward or southward of the heliospheric current sheet, respectively. During the solar cycle, the correlation coefficient changes almost similarly in slow and fast solar wind streams. The dependence of the correlation between BR and BN on the fluctuation frequency was analyzed in a range of 1.2 × 10−5 to 8.3 × 10−3 Hz; it has been found that the correlation is maximal at low frequencies and that it slowly decreases, starting from 10−4 Hz, with increases in the frequency. It has been also found that, fluctuations in the components of the solar wind velocity VR and VN correlate analogously to the IMP components BR and BN at frequencies around 10−4 Hz or higher.
7-15
Dependence of the Geomagnetic Activity on the Structure of Magnetic Clouds
Abstract
The paper studies high-latitude geomagnetic activity with respect to the structural elements of “fast” solar wind magnetic clouds accompanied by shockwaves. A condition for the occurrence of such clouds and a possible cause of their acceleration in the solar wind have been found. An assumption is made that the turbulent cloud sheaths, the parameters of which are conditioned by the solar wind modified under the influence of the cloud shockwave, contribute to the geomagnetic activity. To estimate the evolution of the accumulating solar wind, the local orientations of the shockwave planes have been determined and the sequence of values of the geoeffective Bz component expected at the magnetospheric boundary in the solar magnetospheric coordinate system has been calculated. Comparison of the AL index dynamics with the values of the Bz component measured by the spacecraft and with the calculated sequence of the Bz values shows that the evolution of the solar wind interplanetary magnetic field (IMF) at the magnetic cloud shockwave over the time of its transport to the magnetosphere must be taken into account.
16-26
Two-Dimensional Phenomenological Model of Ring Current Dynamics in the Earth’s Magnetosphere
Abstract
The dynamics of ring current protons with variable boundary conditions in the inner magnetosphere during a magnetic storm has been studied. The spatial and temporal evolution of differential fluxes of protons in the dipole magnetic field has been calculated. The calculations have been performed with the two-dimensional Phenomenological Model of the Ring Current (PheMRC 2-D) offered by the author, which examines the radial and pitch angle diffusions with consideration of losses due to wave–particle interactions. The simulation begins with the distribution of magnetically quiet time. The model has been tested via comparison of the calculated proton fluxes with values measured on the Polar/MICS satellite during the magnetic storm on October 21–22, 1999. The calculated pitch angle distribution is quite consistent (well) with the experimental data. The model has been compared with the other ring current model (Extended Comprehensive Ring Current Model, ECRCM) (Ebihara et al., 2008). PheMRC 2-D is more accurate than ECRCM in describing the experimental data. The offered model can be used to simulate the dynamics of charged particles in the Jovian and Saturn magnetospheres.
27-34
Dynamics of Ionospheric Alfvén Resonances from the End of Cycle 21 through Cycle 24 of Solar Activity
Abstract
The results of the study of the dynamics of ionospheric Alfvén resonances (IARs) in a range of 0–10 Hz based on data from magnetic field observations at the midlatitude Borok observatory (L = 2.8) from the end of solar cycle 21 through solar cycle 24 are presented. It is shown that IARs in 30% of events are accompanied by the simultaneous observation of structured Pc1 geomagnetic pulsations (“pearls”) and IARs are recorded in 70% of events without Pc1 excitation. A specific feature of pearls is that they are observed predominantly at a frequency of the IAR first resonance band. The qualitative coincidence of the dynamics of frequencies of IAR and Pc1 wave packets is detected in 80% of events. The probability maximum of IAR observation falls in the hours before midnight (2000–2200 MLT). IAR seasonal variation is characterized by the presence of two equinoctial maxima. It is shown that the 11-year variation in the IAR emission is controlled by the dynamics of some parameters of the solar wind and IMF. The probability of IAR observation is maximal (in years of solar activity minima) when the ratio of the proton density to the helium ion (α particle) density Np/Na (we note that it is customary to use the inverse, i.e., Na/Np, for the solar wind) and parameter β (which characterizes the ratio of thermal pressure to magnetic pressure) reach the maximum values, while the dynamic pressure of solar wind Pdyn (which controls the magnetosphere compression) is decreased. The coincidence of the dynamics of the frequencies of the IAR first resonance band and pearls, as well as of their seasonal and cyclic variations, may be evidence of the interrelation of these oscillatory processes and the possible common mechanism of their generation.
35-44
Assessment of the Accuracy of Calculations Using the International Reference Ionosphere Model IRI-2016: I. Electron Densities
Abstract
The paper quantitatively compares the results of calculations of the electron density Ne by the International Reference Ionosphere model IRI-2016 with experimental data obtained from the DE-2 satellite. It considers 648 variants of heliogeophysical conditions. The deviation of theoretical estimates from experimental values is within the instrumental accuracy of satellite data in an average of 27% of cases. It is concluded that the IRI-2016 model, the approximation coefficients of which in functional dependences are associated with heights of the F-region, gives negative values of the efficiency coefficient of the predicted electron density in ~73% of cases in the outer ionosphere at altitudes over 500 km.
45-52
The Influence of Cyclonic Activity on the Geomagnetic Field Disturbance
Abstract
The results of observations of geomagnetic disturbances related to cyclonic activity in the troposphere are reported. To reveal these disturbances, we use data on magnetic observations statistically processed for a certain period and data obtained during an individual large cyclone. We propose a physical mechanism by which tropospheric cyclones can produce disturbances in the magnetic field; this mechanism is based on the electrodynamical effect of generation of the magnetic field, while charged clouds move under the action of wind and charged particles precipitate. It has been deduced from the experiments that, in a frequency range of 4.3−8.3 mHz, the dispersion of the magnetic field disturbances may increase by more than two times during cyclone passage above the observational site, as compared to the background values in the cyclone absence. The theoretically estimated amplitudes of the magnetic induction disturbances caused by the cyclone satisfactorily agree with the observational data.
53-61
Geomagnetic Disturbances Accompanying the Great Japanese Earthquake of March 11, 2011
Abstract
This work analyzes the geomagnetic field variations recorded at the Magnetic Observatory of Karazin Kharkiv National University (in the period range of 1–1000 s) that accompanied the Japanese earthquake of March 11, 2011. Due to strong magnetic disturbances before and on the day of the main shock, the magnetic precursor was not identified. The geomagnetic field variations that followed the main shock were detected. If the disturbances are related to the earthquake, their propagation velocities are 2.2 km/s and 240–800 m/s. Such velocities are typical for seismic and acoustic-gravity waves, respectively. Long-period (20, 60, and 100–120 min), almost synchronous variations in the geomagnetic field level with an amplitude of 4–8 nT were found following the earthquake. The delay time of the leading edge of these disturbances increased with increasing distance between the epicenter and the observatory, while their amplitude decreased. The geomagnetic field disturbances were most likely transported by means of slow MHD waves.
62-75
Variations in the Power Spectral Density of Thunderstorm Discharge Pulses in the Frequency Band of 12–40 kHz Associated with Earthquakes in Japan and Taiwan
Abstract
Records of the electric component of the electromagnetic field in the Magadan region indicate abnormal variations in the power spectral density of pulsed signals of thunderstorm discharges (atmospherics) in the 12–40 kHz frequency band during the preparation of several earthquakes on Kyushu Island (Japan) in April 2016. The anomalies were manifested by the unusual behavior of the ratio of spectral densities of atmospherics for higher and lower frequencies. The time dependence of the ratio of spectral densities was slightly distorted, and its values were decreased in the daytime for 3 weeks with a subsequent increase in the daytime minima and emerging outliers of daytime values 3 days before the start of earthquakes. The combination of these anomalies was a precursor of the earthquake series. The detected anomalies were partially observed before the strong earthquakes in Taiwan from October 2013 to February 2016. The anomalies are not associated with geomagnetic activity.
76-89
Potential Predictability and Forecasting of the State of the Field of Anomalies of the Total Electron Concentration from Observational Data
Abstract
An attempt is made in this study to evaluate the potential predictability of the TEC field (its deviation from the weekly average) at hourly time scales based on observational data. The method is based on the calculation of the distance between the group of observations and its subsample (group of analogues) contaning pairs of points separated in time but at minimum distance from each other. The time of potential predictability is defined as the time at which the distance between the two groups becomes close to the root-mean-square distance over the archive of observations. Calculations performed for the TEC SDDIS NASA data archive give the predictability time for anomalies within 6–12 h. Strong anomalies of the TEC field are characterized by the highest predictability; the predictability is maximal for the winter hemispheres and in years of high solar activity (1999–2004 and 2011–2015). These conclusions are confirmed by the forecasts based on the simplest empirical linear dynamic stochastic model. The forecasting calculations also show that there are statistical relationships between the predictability time and the minima/maxima of daily values of the F10.7 and ap indices.
90-100
Anomalous Ionospheric Reflections from the Irkutsk Chirp Ionosonde Data for 2012–2016
Abstract
Vertical ionograms often contain traces of reflections that cannot be attributed to any type of the sporadic Es layer and are classified as anomalous reflections. Vertical sounding data at middle latitudes (Irkutsk) for 2012–2016 are used to study the morphological features of anomalous ionospheric reflections displayed in ionograms at virtual heights of 130–200 km. Characteristic daily, seasonal, and year-to-year variations are identified.
101-104
Effect of the Madden–Julian Oscillation and Quasi-Biennial Oscillation on the Dynamics of Extratropical Stratosphere
Abstract
The effects of the Madden–Julian oscillation and quasi-biennial oscillation in the equatorial stratosphere on the dynamic processes in the extratropical stratosphere has been studied with the use of a model of the middle and upper atmospheric circulation. The heat source of the Madden–Julian oscillation in tropics is specified as a longitude-modulated wave perturbation with a zonal wavenumber of m = 2 and a period of about Т = 45 days that propagates eastward with a phase speed of ~5 m/s. Ensemble calculations were carried out independently for the westerly and easterly phases of the quasi-biennial oscillation. Analysis of the results has shown that both phenomena strongly affect the circulation of the winter extratropical stratosphere, the polar vortex decay, and sudden stratospheric warming events; the character of the effect depends on the combination of their phases. The good agreement between the simulation results and the reanalysis of data confirms our results.
105-114
Features of Geomagnetic Field Secular Variation at the Midlatitude Mikhnevo and Belsk Observatories
Abstract
The data from observation of the geomagnetic field variations at the Midlatitude Mikhnevo Geophysical Observatory of Institute of Geosphere Dynamics of the Russian Academy of Sciences, Mikhnevo village, Moscow oblast, Russia (coordinates 54.959° N; 37.766° E) and at the INTERMAGNET international magnetic network station of the Belsk Geophysical Observatory of Geophysical Institute of the Polish Academy of Sciences, Belsk, Poland (coordinates 51.837° N, 20.792° E) in 2008−2016 are analyzed. A long-term trend related to secular variation in the magnetic field of the Earth is studied by the daily-mean values. Annual variation is distinguished in the north horizontal component of the magnetic field. The reliability of the recent version of the International Geomagnetic Reference Field (IGRF-12) model, which was released in December 2014 to describe variations in the main magnetic field at the Mikhnevo and Belsk observatories, is estimated. The 2011 and 2014 jerks are identified.
115-126