


Vol 58, No 2 (2018)
- Year: 2018
- Articles: 17
- URL: https://journals.rcsi.science/0016-7932/issue/view/9509
Article
Studying the Relationship between High-Latitude Geomagnetic Activity and Parameters of Interplanetary Magnetic Clouds with the Use of Artificial Neural Networks
Abstract
The cause-and-effect relations of the dynamics of high-latitude geomagnetic activity (in terms of the AL index) and the type of the magnetic cloud of the solar wind are studied with the use of artificial neural networks. A recurrent neural network model has been created based on the search for the optimal physically coupled input and output parameters characterizing the action of a plasma flux belonging to a certain magnetic cloud type on the magnetosphere. It has been shown that, with IMF components as input parameters of neural networks with allowance for a 90-min prehistory, it is possible to retrieve the AL sequence with an accuracy to ~80%. The successful retrieval of the AL dynamics by the used data indicates the presence of a close nonlinear connection of the AL index with cloud parameters. The created neural network models can be applied with high efficiency to retrieve the AL index, both in periods of isolated magnetospheric substorms and in periods of the interaction between the Earth’s magnetosphere and magnetic clouds of different types. The developed model of AL index retrieval can be used to detect magnetic clouds.



Main Properties of Forbush Effects Related to High-Speed Streams from Coronal Holes
Abstract
The IZMIRAN database of Forbush effects and interplanetary disturbances was used to study features of the action of high-speed solar wind streams from coronal holes on cosmic rays. Three hundred and fifty Forbush effects created by coronal holes without other actions were distinguished. The mean values and distributions have been found for different characteristics of events from this group and compared with all Forbush effects and Forbush effects caused by coronal ejections. Despite the great differences in high-speed streams from coronal holes, this group turned out to be more compact and uniform as compared to events related to coronal ejections. Regression dependences and correlation relations between different parameters of events for the studied groups have been obtained. It has been shown that Forbush effects caused by coronal ejections depend considerably more strongly on the characteristics of interplanetary disturbances as compared to Forbush effects related to coronal holes. This suggests a significant difference between the modulation mechanisms of Forbush effects of different types and corroborates earlier conclusions based on indirect data.



Galactic Cosmic Ray Intensity in the Upcoming Minimum of the Solar Activity Cycle
Abstract
During the prolonged and deep minimum of solar activity between cycles 23 and 24, an unusual behavior of the heliospheric characteristics and increased intensity of galactic cosmic rays (GCRs) near the Earth’s orbit were observed. The maximum of the current solar cycle 24 is lower than the previous one, and the decline in solar and, therefore, heliospheric activity is expected to continue in the next cycle. In these conditions, it is important for an understanding of the process of GCR modulation in the heliosphere, as well as for applied purposes (evaluation of the radiation safety of planned space flights, etc.), to estimate quantitatively the possible GCR characteristics near the Earth in the upcoming solar minimum (~2019–2020). Our estimation is based on the prediction of the heliospheric characteristics that are important for cosmic ray modulation, as well as on numeric calculations of GCR intensity. Additionally, we consider the distribution of the intensity and other GCR characteristics in the heliosphere and discuss the intercycle variations in the GCR characteristics that are integral for the whole heliosphere (total energy, mean energy, and charge).



Correlation Analysis of Geomagnetic Data Synchronously Recorded by the INTERMAGNET Magnetic Laboratories
Abstract
The results of the analysis of geomagnetic data synchronously recorded by the INTERMAGNET magnetic stations are presented. The goal of this research was to distinguish internal correlations between the data and to determine the optimal spatial interval of the geographical coordinates within which the efficient operation of only one magnetic observatory would be satisfactory in most occasions. The results of the observation of correlations between the geomagnetic data on a global scale are summarized and presented. Possible regions of application of these results are determined.



Statistical Study of the Characteristics of Isolated Bursts of Midlatitude Pi2 Geomagnetic Pulsations
Abstract
The characteristics and interplanetary excitation conditions of isolated bursts of Pi2 geomagnetic pulsations observed during the development of magnetospheric substorms (substorm Pi2) and in its absence (nonsubstorm Pi2) on the night side of the Earth are comparatively analyzed. It is shown that, regardless of the local time and season, the amplitude of isolated Pi2 substorm bursts is always higher than that of the nonsubstorm ones, and the periods and duration of the wave packets of substorm Pi2 bursts are less than those of nonsubstorms. Diurnal and seasonal variations in the characteristics of the two groups of Pi2 bursts differ in the form and position of maxima and minima. It is found that the start of excitation of isolated Pi2 bursts, during substorms and in its absence, is controlled by the preferred direction of the interplanetary magnetic field (IMF) vector perpendicular to the Sun–Earth line (angle θxB = arccos(Bx/B) → 90°). It is assumed that isolated Pi2 bursts of both groups are triggered by reorientation of the IMF vector in the ecliptic plane and the plane perpendicular to it ~15 min before their onset. The most likely source of midlatitude isolated Pi2 bursts during substorm development and in its absence are bursty bulk flows (BBFs) in the plasma sheet of the magnetospheric tail, the regularities of which coincide in many respects with the observed features of Pi2 bursts.



Geomagnetic Storm Effects at F1 Layer Altitudes in Various Periods of Solar Activity (Irkutsk Station)
Abstract
The influence of geomagnetic disturbances on electron density Ne at F1 layer altitudes in different conditions of solar activity during the autumnal and vernal seasons of 2003–2015, according to the data from the Irkutsk digital ionospheric station (52° N, 104° Е) is examined. Variations of Ne at heights of 150–190 km during the periods of twenty medium-scale and strong geomagnetic storms have been analyzed. At these specified heights, a vernal–autumn asymmetry of geomagnetic storm effects is discovered in all periods of solar activity of 2003–2015: a considerable Ne decrease at a height of 190 km and a weaker effect at lower levels during the autumnal storms. During vernal storms, no significant Ne decrease as compared with quiet conditions was registered over the entire analyzed interval of 150−190 km.



Comparison of Ionospheric Parameters during Similar Geomagnetic Storms
Abstract
The degree of closeness of ionospheric parameters during one magnetic storm and of the same parameters during another, similar, storm is estimated. Overall, four storms—two pairs of storms close in structure and appearance according to recording of the magnetic field Х-component—were analyzed. The examination was based on data from Sodankyla observatory (Finland). The f-graphs of the ionospheric vertical sounding, magnetometer data, and riometer data on absorption were used. The main results are as follows. The values of the critical frequencies foF2, foF1, and foE for different but similar magnetic storms differ insignificantly. In the daytime, the difference is on average 6% (from 0 to 11.1%) for all ionospheric layers. In the nighttime conditions, the difference for foF2 is 4%. The nighttime values of foEs differ on average by 20%. These estimates potentially make it possible to forecast ionospheric parameters for a particular storm.



Equatorial Plasma Bubbles: Effect of Thermospheric Winds Modulated by DE3 Tidal Waves
Abstract
A hypothesis about the effect of the tropospheric source on the longitudinal distributions of the equatorial plasma bubbles observed in the topside ionosphere was proposed earlier. It was supposed that this influence is transferred mainly by the thermospheric winds modulated by the DE3 tropospheric tidal waves. This conclusion was based on the discovered high degree correlation (R ≅ 0.79) between the variations of the longitudinal distribution of the plasma bubbles and the neutral atmospheric density. In this work, the hypothesis of the effect of the thermospheric tidal waves on the plasma bubbles at the stage of their generation is subjected to further verification. With this purpose, the longitudinal distributions of the frequency of the plasma bubble observations at the different ionospheric altitudes (~600 km, ROCSAT-1; ~1100 km, ISS-b) are analyzed; their principal similarity is revealed. Comparative analysis of these distributions with the longitudinal profile of the deviations of the zonal thermospheric wind (~400 km, CHAMP) modulated by the DE3 tidal wave is carried out; their considerable correlation (R ≅ 0.69) is revealed. We conclude that the longitudinal variations of the zonal wind associated with DE3 tidal waves can effect the longitudinal variations in the appearance frequency of the initial “seeding” perturbations, which further evolve into the plasma bubbles.



Possible Mechanism for Damping of Electrostatic Instability Related to Inhomogeneous Distribution of Energy Density in the Auroral Ionosphere
Abstract
Satellite observations show that the electrostatic instability, which is expected to occur in most cases due to an inhomogeneous energy density caused by a strongly inhomogeneous transverse electric field (shear of plasma convection velocity), occasionally does not develop inside nonlinear plasma structures in the auroral ionosphere, even though the velocity shear is sufficient for its excitation. In this paper, it is shown that the instability damping can be caused by out-of-phase variations of the electric field and field-aligned current acting in these structures. Therefore, the mismatch of sources of free energy required for the wave generation nearly nullifies their common effect.



Spread F in the Midlatitude Ionosphere According to DPS-4 Ionosonde Data
Abstract
The results of studying spread F obtained from the DPS-4 ionosonde data at the observatory of the Pushkov Institute of Terrestrial Magnetism, Ionosphere, and Radio Wave Propagation (Moscow) are presented. The methodical questions that arise during the study of a spread F phenomenon in the ionosphere are considered; the current results of terrestrial observations are compared with previously published data and the results of sounding onboard an Earth-satellite vehicle. The automated algorithm for estimation of the intensity of frequency spread F, which was developed by the authors and was successfully verified via comparison of the data of the digisonde DPS-4 and the results of manual processing, is described. The algorithm makes it possible to quantify the intensity of spread F in megahertz (the dFs parameter) and in the number of points (0, 1, 2, 3). The strongest spread (3 points) is shown to be most likely around midnight, while the weakest spread (0 points) is highly likely to occur during the daytime. The diurnal distribution of a 1–2 point spread F in the winter indicates the presence of additional maxima at 0300–0600 UT and 1400–1700 UT, which may appear due to the terminator. Despite the large volume of processed data, we can not definitively state that the appearance of spread F depends on the magnetic activity indices Kp, Dst, and AL, although the values of the dFs frequency spread interval strongly increased both at day and night during the magnetic storm of March 17–22, 2015, especially in the phase of storm recovery on March 20–22.



Correction of Electron Density Profiles in the Low Ionosphere Based on the Data of Vertical Sounding with the IRI Model
Abstract
The method of correcting the daytime vertical profiles of electron plasma frequency in the low ionosphere from International Refererence Ionosphere (IRI) model in accordance with the measured data of the virtual heights and absorption of signal radiowaves (method А1) reflected from the bottom of E-region at vertical sounding (VS) is presented. The method is based on the replacement of the IRI model profile by an approximation of analytical dependence with parameters determined according to VS data and partially by the IRI model. The method is tested by the results of four joint ground-based and rocket experiments carried out in the 1970s at midlatitudes of the European part of Russia upon the launches of high-altitude geophysical rockets of the Vertical series. It is shown that the consideration of both virtual reflection heigths and absorption makes it possible to obtain electron density distributions that show the best agreement with the rocket measurements made at most height ranges in the D- and E-regions. In additional, the obtained distributions account more adequately than the IRI model for the contributions of D- and E-regions to absorption of signals reflected above these regions.



Estimating the Characteristics of Traveling Ionospheric Disturbances from Vertical Incidence Ionograms within a Compound Parabolic Layer Model
Abstract
The characteristic U-shaped traces (cusps) in ionograms are associated with the passage of traveling ionospheric disturbances (TIDs), which lead to horizontal electron density gradients in the ionosphere and, therefore, to off-angle reflections in radio sounding. A new form of representation is considered for daily ionospheric sounding data. A compound parabolic layer model is proposed, which allows analytical calculation of ray paths to speed up the “homing-in” of the rays. Changes in the shape of the trace in the ionogram due to varying the TID characteristics are examined. A discussion is given of the possibilities for estimating TID characteristics from digitized vertical sounding ionograms.



Magnetospheric Effects during the Approach of the Chelyabinsk Meteoroid
Abstract
We have analyzed the observational results for variations in the main geomagnetic field and its fluctuations in the range of periods 1–1000 s that accompanied the approach of the Chelyabinsk space body to the magnetosphere and ionosphere of the Earth. The measurements were conducted with a magnetometerfluxmeter near the city of Kharkiv, as well as with the network of magnetometers located at the observatories of Novosibirsk, Kyiv, Lviv, Almaty, Khabarovsk, Arti, Borok, and Yakutsk. Variations in the main geomagnetic field and its fluctuations approximately 33–47 min prior to the explosion of the Chelyabinsk meteoroid have been discovered; they persisted for 25–35 min and were probably associated with meteoroid passage through the magnetosphere. The amplitude of variations reached 1–6 nT. We have proposed a model of the generation of aperiodic, quasi-periodic, and noise-like variations in the geomagnetic field induced by the approach of a space body.



Recording the Response of the Chelyabinsk Meteoroid Fall by Dual-Frequency and Single-Frequency GPS Equipment
Abstract
The Chelyabinsk meteoroid fall has been used to show that an appropriate ionospheric response can be recorded from signals of satellite radar systems. This can be done using dual-frequency or single-frequency equipment. The recording time of the response commencement has been used to estimate the propagation rate of primary disturbance in the atmosphere.



Spatial and Temporal Variations of Infrared Emissions in the Upper Atmosphere. 3. 5.3-μm Nitric Oxide Emission
Abstract
The results of rocket and satellite measurements available in the literature of 5.3-μm nitric oxide emission in the upper atmosphere have been systematized and analyzed. Analytical dependences describing the height distribution of volumetric intensity of 5.3-μm emission of the NO molecule and its variations in a range of heights from 100 to 130 km as a function of the time of year, day, latitude, and solar activity have been obtained.



Propagation of Stationary Planetary Waves in the Upper Atmosphere under Different Solar Activity
Abstract
Numerical modeling of changes in the zonal circulation and amplitudes of stationary planetary waves are performed with an accounting for the impact of solar activity variations on the thermosphere. A thermospheric version of the Middle/Upper Atmosphere Model (MUAM) is used to calculate the circulation in the middle and upper atmosphere at altitudes up to 300 km from the Earth’s surface. Different values of the solar radio emission flux in the thermosphere are specified at a wavelength of 10.7 cm to take into account the solar activity variations. The ionospheric conductivities and their variations in latitude, longitude, and time are taken into account. The calculations are done for the January–February period and the conditions of low, medium, and high solar activity. It was shown that, during high-activity periods, the zonal wind velocities increases at altitudes exceeding 150 km and decreases in the lower layers. The amplitudes of planetary waves at high solar activity with respect to the altitude above 120 km or below 100 km, respectively, are smaller or larger than those at low activity. These differences correspond to the calculated changes in the refractive index of the atmosphere for stationary planetary waves and the Eliassen–Palm flux. Changes in the conditions for the propagation and reflection of stationary planetary waves in the thermosphere may influence the variations in their amplitudes and the atmospheric circulation, including the lower altitudes of the middle atmosphere.



Effect of Electron Precipitations on the Effective Recombination Coefficient
Abstract
The results of an analysis of the possible effect of auroral electron fluxes on the effective recombination coefficient αeff in the ionosphere are presented. It is shown that the αeff value in the E-region of the ionosphere is determined mainly by the physical-chemical properties of the medium. In the F1-layer of the ionosphere, the effective recombination coefficient becomes dependent on both the value of the energy flux and the type of the energy spectrum of the auroral electron flux.


