Geomagnetism and Aeronomy最新文献

This article discusses the testing of the complexity of the instrumental series of Wolf numbers. The work is initiated by the hypothesis of the existence of a low-dimensional dynamo as a model of the Sun’s magnetic activity. This mechanism produces the observable, in the Takens sense, as a broadband chaotic signal with a dominant 11-year mode (Frick et al., 2022). The time series of Wolf numbers is claimed to be this signal. In this article, we consider two problems. In the first, we describe a method for obtaining the average cycle for the dominant 11-year mode. It is based on the Fisher–Rao metric and the quantum mechanical analog of “probability amplitudes” for cycles. In the second problem, we investigate the algorithmic complexity of the instrumental series of Wolf numbers (SSN2) compared with surrogate data obtained by fractal mixing of this series. The mixing “whitens” the 11-year cycle but retains tuples of 2–3 monthly mean counts. Complexity was estimated as permutation entropy (Bandt et al., 2002). It was hypothesized that if the dominant mode was chaotic in nature, the complexity of the source and surrogate series would be close. Our results do not contradict the hypothesis of a chaotic signal with a single prevalent mode as a time series model of Wolf numbers.

The γ Cas type stars are a group of Be stars with unusually hard X-ray emission and an X-ray luminosity of L_X ~ 10³¹–10³³ erg/s, which is higher than for typical Be stars but less than for massive X-ray binaries with Be components. The temperature of the X-ray emitting plasma reaches values of 10–20 keV or even more, assuming that they emit thermal X-rays. To test the hypotheses on the X-rays formation from this group of stars, the variability of the X-ray and optical emission of γ Cas type stars is analyzed. Regular components of X-ray brightness variations and H, He and FeII line profile variations in spectra of such stars are revealed. The periods of optical and X-ray variability are close and correspond to typical periods of non-radial pulsations (NRPs) of Be stars. That suggests modulation of the wind structure of a Be star as a result of NRPs.

The causes of climate change on Earth represent one of the main questions in modern science. As is known, solar radiation is one of the main factors that determines the physical characteristics of Earth’s atmosphere. Therefore, changes in solar activity cannot but lead to changes in Earth’s climate. It is well known that the Little Ice Age took place on Earth during the Spörer, Maunder, and Dalton deep solar minima. The article analyzes changes in solar activity and Earth’s climate since the beginning of the end of the last global glaciation (approximately 20 000–19 000 years ago). In particular, it is shown that the Mayendorff warming, Dryas coolings, and the Iron Age cooling (in the first millennium BCE) could be associated with changes in solar activity, just like the Little Ice Age.

Using statistics from 15 X-ray class M flare events, the features of the position and orientation of magnetic flux ropes in the general spatial structure of the magnetic field of the active regions (ARs) during flares and coronal mass ejections (CME) were studied by reconstructing the coronal magnetic field from the photosphere to the corona (NLFFF extrapolation) for eruptive (with CME) and noneruptive (without CME) active regions. In the considered ARs the most powerful magnetic flux ropes are located near the center of brightness of the microwave flare source. However, weaker flux ropes also exist in other places of the AR. It is shown that in all events without CME, the most powerful ropes are located quasi-perpendicular to the overlying magnetic field lines (the ropes are “closed” by the external field). Various scenarios are observed in CME events: (1) the flux ropes are surrounded by an open magnetic field configuration (three events); (2) the flux ropes are oriented at small angles, quasi-parallel, to the overlying magnetic field lines (three events); (3) the flux ropes are oriented quasi-perpendicular to the external magnetic field (2 events).

The study used the geomagnetic field and hyperspectral remote sensing techniques to acquire information about subsurface characteristics and delineate faults. In this study, ground magnetic surveys were conducted at various locations along the fault in the Kashmir Valley. The study found that the faults are associated with magnetic minima, indicating potential hydraulic activities along the fault planes. The anomalies observed in the magnetic field were attributed to oxidation and martitization processes occurring at fault rupture zones. These processes led to a reduction in iron content, resulting in anomalies in linear profiles. The total magnetic intensity (TMI) varied by approximately 25 nT, considering the crustal thickness and lithological characteristics of the study area. This suggests that magnetic studies of the Earth’s crust can be highly effective for fault delineation purposes. Additionally, this study employed hyperspectral remote sensing analysis across the fault profile. This analysis revealed that fault planes exhibited spectral variations. Specifically, spectral reflectance increased consistently with longer wavelengths, which indicates transformation of Fe³⁺ to Fe²⁺. These findings indicate that hyperspectral studies can be well-suited for detecting and validating subsurface faults. The study found that the fault location can be inferred by combining the magnetic anomaly data and hyperspectral remote sensing data. This integrated approach allows for improved fault delineation and a better understanding of subsurface fault characteristics, which are essential for seismological studies.

In a series of studies, the authors have shown that explosive processes (EPs) in active regions (ARs) (such processes include solar flares and coronal mass ejections) can have a significant impact on the characteristics of the magnetic field in the umbra of some sunspots in these ARs. This paper is the first in a planned series of studies in which we will consider various factors that determining the extent of EP influence on the magnetic field in the umbra of sunspots. Using the example of one EP event, we attempted to determine how the size of the sunspots and their position relative to the location of the flare affect the intensity of EP impact on the magnetic field in the umbra of the sunspots.

Solar energetic particle (SEP) events are mostly generated by solar flares. They can be associated not only with flares that occur on the visible side of the Sun but also on the backside. It is noted that the shape of the time profiles of SEP events associated with flares on the back side of the Sun does not correspond to the typical impulsive or gradual time profiles. X-rays are the main source of information about the processes of energy release and particle acceleration in solar flares. For many years, information on this type of emission for flares on the back side of the Sun was rare. Nowadays, the ability to obtain this type of information is becoming more and more available. We present the results of testing numerical model realized as a code that makes it possible to reproduce the shape of the time profile of SEP events using simple assumptions about particle propagation into the interplanetary space. The time profiles of SEP protons with energies above 30 MeV have been modeled assuming that the particles were accelerated only in the solar atmosphere during the flare. Tests have been done for four impulsive flares that occurred in the western hemisphere of the Sun and in the center of the solar disk. We simulated the time profile of an SEP event, the source of which was a flare that possibly occurred on the backside of the Sun on October 21, 2003. The results, possibilities for model improvements, and the application of this method to the study of SEP events with no source on the visible side of the Sun are discussed.

A reconstruction of the average monthly values of sunspot areas—the physical index of solar activity—is proposed. The uncertainty of the obtained values for a significance level (alpha = 0.05) is estimated. The duration of the number of monthly means has become 275 years. It is shown that the AR index, when used in reconstructions of solar activity of historical observations with small telescopes, is more advantageous than the indices of the number of spots or groups thereof. This index is not sensitive to the possible loss of small groups, which on average make up about a third of the overall number.

Heliogeophysical features of the 21st century are considered. It is discussed that the low solar dynamics of cycles 24 and 25 manifested themselves not only in sunspot number, but also as a significant decrease in geomagnetic events, decreased intensity of solar cosmic rays, and increased intensity of galactic cosmic rays. Changes in the solar GMF and a significant decrease in the amplitude of odd harmonics of the global magnetic field (GMF) of the Sun were also observed. It is proposed to use the maximum of the fifth zonal harmonic of the solar GMF as a predictor of the time of the maximum of the 11-year solar activity cycle, and the polar field of the Sun to predict the height of the cycle. The maximum of the 25th cycle of solar activity (SA) predicted by the authors was expected at the end of 2023–beginning of 2024 with a cycle height of no more than 131. A secondary solar activity maximum is possible during 2025. Epidemiological processes can serve as an additional predictor of global changes in solar activity. The number of viral pandemics during the 19th–21st centuries was tripled near centennial solar activity minima. Measles epidemics are developing approximately a year prior to the onset of extrema of the 11-year solar activity cycle. It is emphasized that the role of solar activity minima in the development of viral epidemics is significantly underestimated.

This paper is devoted to the study of the interaction between nonthermal electrons injected into a flare loop and whistler turbulence in it. The features of redistributions of nonthermal electrons by energy and pitch angle are considered during their interaction with whistlers having spectra of different amplitudes, bandwidths, and central frequencies. We show, in particular, that this interaction results in an efficient and fast (seconds) acceleration of electrons in the energy range of 200–3000 keV, which leads to a significant flattening of their energy spectrum. The most efficient acceleration of high-energy electrons occurs by turbulence with low central frequencies, wide bandwidths, and large amplitudes. In this case, their concentration with energies above 1000 keV can increase by several orders of magnitude.