Geomagnetism and Aeronomy最新文献

The article develops a method for determining the geomagnetic cutoff rigidity based on tracing of charged particles in Earth’s magnetic field using the particle-in-cell method implemented in the Buneman–Boris scheme. In order to test the method, the geomagnetic cutoff rigidity in the field of an ideal dipole and in the field given by the IGRF model are calculated. In the first case, the obtained data are compared with analytical values. The calculation accuracy in this case is 3 MV. In the second case, the penumbra pattern is reproduced in different geographical locations, for different periods, and the stability of the method to small perturbations of the initial parameters is investigated. As the main results, the article constructs and analyzes geomagnetic cutoff rigidity maps at low-orbit satellite altitudes for different directions in space as well as their variations from 1900 to 2015.

The results of an analysis of some irregularities in a series of coordinates of the shift in the geographic North Pole along Earth’s surface are presented in order to establish a temporal relationship between their appearance and some global jerks in the geomagnetic field. The calculations used average daily data from the IERS service on movement of the North Pole from 1962 to 2021, as well as information on global jerks in the geomagnetic field at all magnetic observatories on the globe. To identify and analyze irregularities in the movement of the pole along the Earth’s surface, the following methods were used: Fourier methods and wavelet analysis of time series, methods for determining the threshold of a fixed shape and minimax in the procedure for analyzing non-Gaussian noise, methods of phase and pseudophase space, as well as the stroboscopic method of constructing the Poincaré map. Analysis of local Fourier spectra and wavelet spectra reveal irregularities in the shift of the North Pole along the Earth’s surface in the following time intervals: 1967.04.09–1967.11.30, 1974.03.29–1974.09.12, 2005.11.03–2006.03.07, comparable to the appearance of global jerks in 1969, 1978 and local jerks in 2005. It is believed that the changes in energy that caused short-term deviations of the shift in the pole’s trajectory and return to the previous trajectory at cusp points are associated with singularities in the interaction of oscillations in Earth’s rotational and translational motion in the Solar System. The time of the appearance of irregularities on the graphs of the polar shift along the Earth’s surface in 1967 and 1974 is ahead of the time of the appearance of global jerks in the geomagnetic field.

The article discusses the observation methodology, data interpretation, and results of electromagnetic monitoring with a controlled source for one of the seismically active regions of Siberia—Gorny Altai. Monitoring was carried out during the aftershock period in the epicentral zone of the destructive 2003 Chuya earthquake with M = 7.3. For regular observations, a measurement technique has been developed using several modifications of the transient electromagnetic field (TEM) method to determine variations in electrical resistance and the anisotropy coefficient. Long-term series of these two geoelectric parameters of the section are presented, compared with the characteristics of ongoing seismic events. As a result of the analysis, it was shown that variations in electrical resistance and the electrical anisotropy coefficient reflect the development and gradual decay of the aftershock activity of a powerful earthquake. The advantages of the TEM method and the selected technique for monitoring in complex areas are reflected.

This study is based on the angular width of CMEs from the 23rd and 24th solar cycles. We divided the CMEs seen during the 23rd (1996–2007) and 24th (2008–2017) solar cycles into three categories: Narrow (width ≤ 20°), Intermediate (20° < width < 200°), and Wide (width ≥ 200°). It was found that the 24th solar cycle had twice as much as narrow CMEs than what occurred in the 23rd cycle. Similarly, there were about 1.2 times more intermediate CMEs in the 24th cycle than in the 23rd. Wide CMEs followed a similar trend of 1.3 times the number found for the 23rd cycle. Both cycles followed an analogous trend with respect to the number of CMEs based on their angular width. An intriguing find is that the percentage of slow (speed < 500 km/s) CMEs is greater in narrow and intermediate ones in the 23rd and 24th cycles compared to fast CMEs (speed > 500 km/s), whereas it is the opposite with wide CMEs. Wide CMEs are observed to have the highest mean speed among the three groups. Overall, it was found that all three groups of CMEs in the 23rd solar cycle had faster mean, median, maximum, and minimal speeds than those in the 24th cycle.

The article studies variation in the serpentine emission carrier frequency f_SE observed in the 0.1–5.0 Hz frequency range under quiet magnetosphere conditions (Kp ~ 0–2). The data of magnetic field recording at the Antarctic Vostok Observatory (corrected geomagnetic coordinates Φ′ = −85.41°, Λ′ = 69.01°) for 1970‒1972 were used in the analysis. Using the dynamic spectra of ULF emission, we analyzed 90 cases of serpentine emission observation, the center carrier frequency of which gradually decreased (several times, sometimes to 0), then increased almost to the initial level in time intervals significantly exceeding the maximum modulation period (1 h). In this case, typical modulation of the emission carrier frequency with periods of 1–60 min persisted. The most likely time of observation of the detected effect was in the hours before midnight. It is shown that a decrease and subsequent increase in f_SE were observed versus 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 f_SE and dynamics of the AE-index, as well as observation of the effect of a decrease in the carrier frequency near local midnight, it is suggested that serpentine emission is most likely excited near the polar cusp, then penetrates the polar cap region. The behavior of f_SE observed over long time intervals is presumably governed by the plasma parameter β and ratio of the proton density to the helium ion density Np/Na, the dynamics of which are similar to the average variation in f_SE.

The results of measuring VLF signal parameters propagating in the Earth-D-region of the ionosphere waveguide to assess changes in the state of the lower ionosphere as a result of the impact of X-ray radiation of solar flares make it possible to obtain qualitative data on the nature and magnitude of the impact. Obtaining accurate data on the relationship between changes in electron concentration and flare parameters and reliable prediction of the conditions of LF radio signal propagation during strong geophysical disturbances is complicated by the lack of complete information on the frequency spectrum of X-ray radiation for a particular flare and data on the ionization rate of the ionosphere for flares of different classes. The technique of determining the X-ray spectrum in a wide range of wavelengths and calculating the ionization coefficients of the lower ionosphere as a function of the ionizing radiation parameters of flares, presented by Ryakhovsky et al. (2023), makes it possible to improve the accuracy in estimating variations in the parameters of the lower ionosphere. The present paper is devoted to verifying the performance of the developed empirical model of lower ionization of the lower ionosphere at the solar flare front and comparing the results with experimental data on the variation of VLF radio parameters.

We analyzed 214 events of ‘polar’ substorms on the Scandinavian meridian IMAGE, i.e., substorms recorded by magnetometers located at geomagnetic latitudes above ~70° MLAT at 1900−0200 MLT during a magnetically quiet time in the absence of negative magnetic bays at lower latitudes. The Harang discontinuity, which separates the westward and eastward electrojets by latitude, is a typical structure for the indicated MLT sector of the high-latitude ionosphere. The global distribution of ionospheric electrojets and the location of the Harang discontinuity during development of ‘polar’ substorms were studied using the maps compiled from the results of spherical harmonic analysis of magnetic measurements on 66 simultaneous ionospheric communications satellites of the AMPERE project. Based on analysis of these maps, it is shown that the instantaneous location of the equatorial boundary of the ionospheric current of a ‘polar’ substorm determines the instantaneous location of the polar boundary of the Harang discontinuity, and the polar boundary of the eastward electrojet determines its equatorial boundary. It has been established that the appearance of 90% of ‘polar’ substorms is observed simultaneously with increasing planetary substorm activity according to the AL-index and development of a magnetospheric substorm in the postmidnight sector. At the same time, the development of evening ‘polar’ substorms is associated with the formation of near-midnight magnetic vortices at geomagnetic latitudes of ~70° MLAT (near the “nose” of the Harang discontinuity), indicating a sharp local enhancement of the field-aligned currents. This leads to the formation of a new substorm in the evening sector of near-polar latitudes, called a ‘polar’ substorm with typical features of the onset of a substorm (Pi2 geomagnetic pulsation bursts, sudden onset of the substorm close to the equatorial boundary of the contracted oval (the development of a “substorm current wedge”, etc.)

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.

Based on the data of 17 mid-latitude ionospheric stations for 1958–1988, the study analyzes seasonal features of the F2 layer peak concentration (NmF2) at different longitudes with enhanced (48 > ap(τ) > 27) geomagnetic activity, where ap(τ) is the weighted average (with a characteristic time of 14 h) ap-index of this activity. As the characteristics of the NmF2 variability, the standard deviation σ of NmF2 fluctuations relative to quiet level and the average shift of these fluctuations x_ave during daytime (1100–1300 LT) and nighttime (2300–0100 LT) were used. It was found that at all analyzed stations, the dispersion σ² for enhanced geomagnetic activity is greater than for quiet conditions, and, other things being equal, it is maximum in winter at night. For enhanced geomagnetic activity in all seasons, the difference in x_ave values between the analyzed stations is quite large. One of the reasons for this difference is associated with the dependence of x_ave on geomagnetic latitudes. To select these latitudes, approximations of the geomagnetic field with tilted dipole (TD), eccentric dipole (ED), or with corrected geomagnetic (CGM) coordinates were used. It was found that the x_ave dependence on the ED latitude is more accurate in comparison to the x_ave dependence on the TD latitude or CGM latitude during all seasons at night, and during equinoxes and winter, in the daytime. In summer, in the daytime hours, the x_ave dependences on ED latitude and CGM latitude are comparable in accuracy, and they are more accurate compared to the x_ave dependence on TD latitude. Consequently, ED latitudes are optimal for taking into account the effects of storms in the F2 layer peak concentration at mid-latitudes during all seasons. This conclusion has apparently been made for the first time.

The results of the “Terminator” space experiment on board the International Space Station are presented. Images of Earth’s atmosphere are obtained in the near IR spectral range with the limb geometry of observations under a full moon. The calculated vertical profiles of volume emission/scattering rate point that the aerosol layer occurs within the height region of 80–100 km in Earth’s atmosphere. It is proposed that this layer is meteoric in origin. Estimates show that the size spectrum of aerosol particles lies within the 1–100 nm range.