Geomagnetism and Aeronomy

Abstract

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.

Abstract

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.

Abstract

The article studies variation in the serpentine emission carrier frequency fSE 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 fSE 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 fSE 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 fSE 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 fSE.

Abstract

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.

Abstract

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 xave 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 xave values between the analyzed stations is quite large. One of the reasons for this difference is associated with the dependence of xave 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 xave dependence on the ED latitude is more accurate in comparison to the xave 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 xave dependences on ED latitude and CGM latitude are comparable in accuracy, and they are more accurate compared to the xave 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.

Abstract

The presence of ions within the atmospheric region near the soil surface has considerable implications for enhancing our understanding of Earth’s complex systems. This study delves into the intricate relationship between the atmospheric electric field in the boundary layer and lithosphere. The focus was specifically on investigating how soil radon and its progeny influence the production rate of ions in both the soil and the atmosphere. To achieve this, we combined the radon transport equation with advanced machine learning techniques. Using a well-suited machine learning model, we effectively modeled the responses of soil radon and seamlessly integrated them into the radon transport equation. The resulting insights were used to predict the rates at which radon-induced ion pairs were produced. A particularly important parameter is the surface-ion production rate, which is crucial for estimating the amplitude of the near-surface electric field. This methodology was applied to analyze data from two radon monitoring stations in Turkey: Erzincan, located along the North Anatolian Fault (NAF), and Malatya, situated close to the East Anatolian Fault regions. The significance of this estimation approach resonates within the field of lithospheric–atmospheric studies. This innovative methodology holds promise as a valuable tool for future investigations in the domains of lithosphere–atmosphere–ionosphere coupling (LAIC), global electric circuits (GEC), and seismo-ionospheric coupling. Ultimately, this study underscores the importance of carefully considering the intricate interconnections that exist among different components of Earth’s intricate system. This advocates the adoption of novel methods to shed light on these complex interactions.

Abstract

When analyzing a narrowband signal, the Hilbert transform is often used, which makes it possible to describe the process through slowly changing functions: the envelope (amplitude) and, weakly dependent on time, the characteristic signal frequency—the “instantaneous” frequency. Based on the smoothness of these characteristics, one can evaluate the process and compare it at different periods. This approach was used to analyze the spectral components of a series of average monthly Wolf numbers. This description of the main and second harmonics, supplemented by the properties of the long-period component, gives a fairly complete picture of the entire series of monthly averages. The work examines the correspondence of the characteristics of reliable data, with this approach, to the accepted description in terms of the parameters of cycles (maximum of the cycle, duration of the cycle, and its growth branches) and constructs an “envelope” of the maxima of the cycles. The time dynamics of the instantaneous frequencies of the fundamental and second harmonics of the entire series are also presented, and significant differences in their behavior are noted in the intervals corresponding to the reconstructed and reliable parts.

Abstract

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.

Abstract

Active development of the Arctic and increased intensity of navigation along the Northern Sea Route and air traffic in the Arctic Ocean airspace draws attention to the problem of disruptions of transpolar radio wave propagation. In high-latitude regions, the passage of navigation signals of global positioning systems depends on the state of the ionosphere. During geomagnetic disturbances, ionospheric inhomogeneities develop that interfere with satellite positioning systems. The position and shape of auroras depend on the state of the magnetosphere. In this study, the component model of the auroral magnetic field has been calculated for the first time using the updated digital model of the full values of Earth’s magnetic field components of the St. Petersburg Branch of the Institute of Terrestrial Magnetism, Ionosphere, and Radio Wave Propagation of the Russian Academy of Sciences for the first time. The magnetic field of the auroral zone was calculated for heights from 0 to 1000 km for the period from 1900 to 2023, including for heights of 100–110 km, where the intensity of auroras reaches its maximum in the near-Earth space of the Arctic. The spatial displacement of the auroral oval has been estimated for the period from 1957 (its first mathematical description) to the present. As the analysis showed, the displacement of the boundaries of the auroral oval during the period under consideration has occurred in time and in space codirectionally with the displacement of the isolines of the extremes of the horizontal and vertical components of the auroral magnetic field of the Northern Hemisphere.

Abstract

In this study, we consider historical geomagnetic satellite data obtained during a strong magnetic storm on March 8−9, 1970. In addition to the data of the Soviet satellite Kosmos-321, data from the American satellite OGO-6, which performed geomagnetic measurements at the same time, were used. We analyzed time variations of external magnetic fields recorded in satellite and ground-based observations of the magnetic field. The research also gave impetus to the creation of the improved software implementation of the auroral oval model APM, which enables reconstruction of its position and precipitation intensity in both the past and near real time. The magnetic variations originating in the near-Earth space from various sources were identified. In particular, we revealed the signatures of the storm-time ring current and equatorial and auroral electrojects. The paper highlights the enduring value of historical data of magnetic field observations stored in data centers and continuously digitized by their staff.

Abstract

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.

Abstract

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.

Abstract

The effect of a meteorological storm in October 2018 in the Baltic Sea on the state of the mesosphere and lower thermosphere is investigated. The wave activity of internal gravity waves from TIMED/SABER satellite data is analyzed, and the effects of the meteorological storm at heights of 80–100 km are determined. A method based on mode decomposition from SABER data is adapted to calculate the gravity wave potential energy density (GWPED) and to isolate the temperature perturbations caused by their propagation at lower thermospheric heights. Wavelet analysis of the temperature perturbations revealed two ranges of vertical wavelengths, 5–8 km and 14–18 km. In the area of a meteorological storm, the amplitude of internal gravity waves with vertical wavelengths of 5–8 km increases, and the area of their maximum expands and shifts upward to heights of ~90 km, while on meteorologically quiet days these waves are observed at heights of 65–70 km and with smaller amplitudes. Above the area of a meteorological storm at heights of 90–100 km, the values of the gravity wave potential energy density increase significantly compared to quiet days before and after the storm, and the spatial extent of the perturbation area increases.

Abstract

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.)

Abstract

The updated database of Forbush effects and interplanetary disturbances (https://tools.izmiran.ru/feid) is used for an extensive analysis of various characteristics of events caused by the influence of interacting solar wind disturbances on the near-Earth space. In particular, the cases of different combinations of the pair interaction of high-speed streams from coronal holes and coronal mass ejections over the long period from 1995 to 2022 are considered. Variations in the flux of galactic cosmic rays (with a rigidity of 10 GV) and changes in the parameters of the interplanetary medium and geomagnetic activity are described. It is shown that the degree of mutual influence depends on the time between the detection of neighboring events; with the most pronounced changes in various parameters for events whose interaction occurred before reaching Earth’s orbit. It is also established that in interacting solar wind disturbances not only the extremes of the parameters of cosmic rays, interplanetary medium, and geomagnetic activity but also their time profiles are subject to changes.

Abstract

Long-term variations (trends) in the height of the ionospheric F2 layer peak hmF2 is analyzed based on the data of Moscow and Juliusruh stations. The near-noon LT hours and two winter months (January and February) and two summer months (June and July) are considered for a period of 1996–2023. Well-pronounced and statistically significant negative hmF2 trends are found both in summer and winter. Overall, the F2 layer height decreased during the analyzed period by 0.5–1 km per year. The “Delta” method developed and published by the authors earlier is applied to the same data. The results confirm a systematic decrease in the hmF2 value in the past two decades. It is found that the F2 layer height has decreased in recent years more rapidly than in the earlier years.