Geomagnetism and Aeronomy最新文献

Since January 2020, the current solar cycle 25 has begun. Its development in the first four years, according to the Gnevyshev–Ohl rule, brought it into the family of medium-sized cycles. In November 2023, it entered the maximum phase. Therefore, the maximum of the current cycle should take place no later than June 2024 with the expected value of the relative number of sunspots W* = 100+/–10 (150+/–15 in the V2 system). The minimum of the current cycle should be expected in the first half of 2031, and the course of its development on the growth branch shows that it fits into the characteristics of average solar cycles of the epoch of lowered solar activity on the growth branch with its own features. This confirms the stability of the scenario of solar cyclicity for the last ~190 years, which provides for a change in the level of sunspot activity in different epochs of solar activity, increased or lowered, with clearly distinguished transition periods, as a consequence of regular changes in the mode of generation of the total solar magnetic field, with a duration of ~5 cycles.

Vector-magnetograms acquired by the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO) were utilized to explore the spatial correlation functions of the dissipative structures, such as the vertical magnetic field dissipation, E_diss, the squared density of the vertical electric current, (J_{z}^{2}), the current helicity density, H_c. Six mature active regions (ARs) were explored, three of them belong to the magneto-morphological class (MMC) A1—regular ARs that follow the empirical rules of the Babcock-Leighton dynamo theory, and the rest three ARs belong to the MMC B3 class, irregular multipolar ARs. We found that, on the contrary to the vertical magnetic field structures (see (Abramenko, Suleymanova 2024)), all considered here dissipative structures reveal a range of the power law in the correlation function. Parameters of the power law vary significantly for different types of the considered structures and for different ARs of different classes. The most pronounced difference in the power law parameters between the AR’s classes was found for both (J_{z}^{2}) and H_c: the B3-class ARs demonstrate a capability for longer correlations and shallower power law slope than the A1-class ARs do. As soon as the power law correlation function is thought to indicate the self-organized criticality (SOC) state, we might conclude that in the photosphere, the SOC is rather observable in the magnetic dissipative structures, than in the magnetic field itself; a signature of SOC seems to be stronger manifested in the complex irregular B3-class ARs with high flaring activity. The proposed approach can facilitate to find a connection between the photosphere and upper layers in setting up the critical state, which is necessary for eruptions of all scales.

The electron cyclotron waves instability near the frequencies of electron cyclotron harmonics in an electron–positron plasma is studied under conditions typical for the radio emission source with a quasi-harmonic structure of the pulsar in the Crab Nebula. The increment of instability of longitudinal cyclotron waves is calculated for an electron–positron plasma with a small admixture of energetic electrons and positrons with a “loss cone” distribution function. It is shown that the magnitude of this increment increases significantly for the waves with a frequency close to the frequency of the upper hybrid resonance when the latter is close to the frequency of one of the cyclotron harmonics, similar to the double plasma resonance effect in electron–proton plasma.

Samples with a short-term (less than a year) increase in the content of the radioactive isotope ¹⁴C were recently discovered in tree rings, in four cases accompanied by concentration growth of ¹⁰Be and ³⁶Cl in other natural archives. Most publications suggest that this increase is due to a sharp increase in the flux of solar cosmic rays (SCR) at the boundary of the Earth’s atmosphere caused by solar superflares. Other reasons may be connected with the flux rise of the galactic cosmic rays (GCR) as the Solar System passes through a dense interstellar cloud, or a galactic gamma-ray burst. To reconcile the amount of ¹⁴C with cosmogenic isotopes ¹⁰Be and ³⁶Cl formed in the atmosphere, it is necessary to assume that the proton spectra in such superflares should be harder than most modern experimentally recorded ones. Measurements of the ¹⁴C content in lunar regolith cores returned by the Apollo 15 expedition showed a significant drop in radiocarbon concentration to a depth of 5 g/cm², followed by an increase to maximum values at about 50 g/cm² then a decrease. At shallow depths, the contribution from low-energy SCRs predominates, and at large depths, the contribution from high-energy GCRs prevails. Analysis of the depth profile of the ¹⁴Cconcentration makes it possible to establish SCR fluxes and spectra over several radiocarbon half-lives (10 000–20 000 years) and highlight the possible contribution of hypothetical superflares. Our analysis shows that the hypothesis of solar superflares worsens the agreement with the observed depth variations of ¹⁴C in the lunar regolith.

Alfvén waves with periods of a few seconds excited in solar coronal magnetic loops during flare energy release can lead to effective heating of the plasma in the lower atmosphere of the Sun, which is responsible for continuous optical radiation. Meanwhile, the question of the propagation time of these modes from the corona to the photosphere has not yet been considered in detail. Based on solar atmospheric model by Avrett and Loeser (2008), for different values of background magnetic fields, taking into account their height dependence, the estimates of the propagation time of Alfvén waves from the corona to the photosphere were obtained. The characteristic values exceeding several minutes and impose certain restrictions on wave heating of the lower atmosphere of the Sun. The implications of the results are discussed.

The presence of groups of cycles with larger/smaller amplitudes and alternation of these groups suggests the existence of a long-period solar activity (SA) cycle with epochs of increased/decreased activity. Since SA and its changes significantly influence climate and humans across the near-Earth space, it is reasonable to have a portrait (template) that reflects the main characteristics of these groups, making it possible to qualitatively and semiquantitatively assesses of SA epochs in the past and future. In the study, the properties of epochs SA of maximum/minimum are determined by the characteristics of reliable cycles 10–23 (14 cycles, a total period of 153 years, and the relationship between the amplitude of the cycles and their duration is taken into account). The formation of the pattern is based on the “envelope” of the maxima of these cycles. The possibility of correcting the Dalton minimum is discussed and a long-term forecast of SA is constructed.

El Niño (ENSO), a consequence of changes in ocean circulation patterns, has a significant impact on the global climate and associated economic activity. According to our hypothesis, in addition to internal climatic factors, the ocean circulation regime can be controlled by small changes in total solar irradiation (TSI) occurring in the 11-year solar activity cycle. In this case, positive feedback with a gain of about 10 is possible in near-equatorial regions. In this paper, we attempt to predict monthly averages of an index describing ENSO using TSI as an additional predictor. For prediction, we train a recurrent neural network with a long- and short-term memory (LSTM) unit on ENSO alone and with the addition of TSI. As a result, we find that the ENSO training error is reduced when TSI is added as a predictor. Our result indicates the possibility of using TSI as one of the predictors in constructing modern nonlinear predictive global climate models.

Based on a large volume of observational data of magnetic fields obtained at both ground-based and space observatories, cyclical variations of the meridional flows of the solar magnetic fields in 21–25 cycles of solar activity are considered. It is shown that magnetic fields of medium strength of different polarities form oppositely directed magnetic fluxes moving from one pole to the opposite, with a period of about 22 years. Flows of high-strength magnetic fields migrate from high to low latitudes symmetrically in both hemispheres with a period of about 11 years. The interaction of multidirectional magnetic fluxes of medium and strong magnetic fields leads to sharp changes in the structure of the global magnetic field, latitudinal redistribution of magnetic fields of positive and negative polarity, the formation of a sector structure of the global magnetic field at the maximum and a zonal structure at the minimum of solar activity, and a change in sign of the magnetic field at the poles of the Sun.

We propose a model of a light bridge as a current-carrying magnetic flux tube formed by convection. It is shown that convection in the sunspot penumbra provides the electric current necessary to heat the flux rope plasma and forms structures of a light bridge type. The steady-state heating mode of the light bridge is considered, since the light bridge life time (days) is much longer than the typical heating time (minutes). Radiation losses determine the current value I > 10¹¹A required to heat the light bridge to a temperature up to 6800 K. The parameters of the light bridge plasma are presented, and the observed double structure of the light bridge emission is explained.

This paper presents another model of a flare filament with a force-free magnetic field structure. The distribution of the magnetic field and currents within the volume of the rope is defined by the so-called flux function. To obtain a force-free solution, the Laplacian of this function must strictly depend only on the function itself. However, there are a large number of such functions, which raises the question: how does the choice of a particular flux function affect the physical properties of the magnetic flux rope constructed based on it? In previous studies, the author generally used an exponential dependence of the flux function on the coordinates, but in this article, a power function was used, and it turned out that the physical parameters of the flare ropes almost coincide. All force-free magnetic flux ropes have one common physical property: as the rope loop apex extends into the corona, the external pressure that prevents its lateral expansion steadily decreases, and upon reaching a certain critical reduction, the longitudinal magnetic field of the rope turns to zero at the current inversion surface (CIS). At this point, the force-free parameter and the azimuthal electric current experience a discontinuity at this surface, causing their values in the vicinity of the CIS to grow indefinitely (in magnitude). The electron drift velocity here inevitably exceeds the ion acoustic velocity, leading to the excitation of plasma ion-acoustic instability, a sharp drop in plasma conductivity within the rope, and the generation of a super-Dreicer electric field. Parker’s effect (alignment, with some delay, of the torque along the rope axis due to the transfer of azimuthal field to the energy release region) leads to quasi-periodic pulsations of hard flare radiation and ultimately ensures the flare release of a significant portion of the free magnetic energy stored in the long loop of the magnetic flux rope.