Geomagnetism and Aeronomy最新文献

In this paper, the dynamics of loop-like structures and related phenomena during the solar flare on February 24, 2023 are investigated. A new character of the dynamics of the coronal loop system during the flare has been studied, consisting in compression (lowering) of the loops both during the growth and decay phases of the flare. It was found that a sharp decrease in height began with the appearance of intense nonstationary plasma fluxes (ejections) observed mainly in the vicinity of the eastern footpoints of the coronal loop system. It was concluded that the rapid (at a speed of up to 25 km/s) compression of the coronal loop system can be explained by a decrease in free magnetic energy (a decrease in the vortex phi-component of the magnetic field) caused by the observed non-stationary plasma eruptions from the vicinity of the loops, as well as possible Joule dissipation of electric currents in the loops.

We present the results of a statistical study of the characteristics of active regions (ARs) and ribbons associated with flares of GOES class M5.0 and larger, occurring from February 2011 to December 2022 within 40° of the central meridian. A total of 60 flares met these criteria, of which 39 were eruptive and 21 confined. We used SDO/HMI and SDO/AIA data to obtain the magnetic reconnection fluxes and rates. Magnetic reconnection fluxes and ribbon areas of confined and eruptive flares correlate with the flares GOES class. For flares of the same GOES class in confined events, compared to eruptive ones, the mean magnetic flux density in the ribbon is higher. Reconnection rates in confined and eruptive flares showed a temporal evolution similar to observed hard X-ray (HXR) emission. The fraction of AR involved in reconnection is larger in eruptive flares and for both types of events it decreases with increasing distance between the flare and the AR center. For the same fraction of AR involved in the flare, eruptive events, compared to confined ones, are located at distances twice as far from the AR center. Eruptive flares tend to occur in compact ARs at the periphery, while confined ones occur in extended ARs near the center.

The seismo-electromagnetic studies have been in progress since 1998 at Agra station. In the present paper, ionospheric GPS-TEC, ground-based ULF/VLF measurements were investigated in light of four strong earthquakes (M ≥ 6.8) that occurred around the Indian subcontinent in different periods. These three datasets are processed by using advanced signal-processing techniques in time and frequency domains. To analyze these datasets, a period of 16 days (including the day of the earthquake) was considered. For each day, only one minute of data was taken into account, with the time of the earthquake being the midpoint of that minute. The precursors are obtained in all the datasets considered before the occurrence of earthquakes. In TEC, ULF, and VLF data, significant changes are observed 2 to 15, 2 to 7, and 5 to 13 days before earthquakes, respectively. Significant results are obtained in time and frequency domains and the variations of solar and magnetic storm activities have also been examined thoroughly to check the validity of these variations. Further, these variations are interpreted in terms of lithosphere-atmosphere-ionosphere coupling mechanisms available in the literature.

The occurrence of geomagnetic storms and the variation in the geomagnetic storm indices during the ascending phase of solar cycle 24 has been examined. The parameters considered for this study includes; IMF Bz (nT), solar wind speed (({{{v}}_{x}}), in km/s), Dst index (nT), Aurora Electroject (AE, AU and AL indices in nT), and sunspot number. The datasets span from 2010 to 2012. Results of the study reveals that; the frequency of occurrence of geomagnetic storms increases with the increase in solar activity. Six (6) geomagnetic storms were recorded in 2010 (with sunspot number, Rz = 16.5), 13 storms in 2012 (with sunspot number Rz = 55.7), and 17 storms occurred in 2012 (with sunspot number, Rz = 57.5) giving a total of 36 geomagnetic storm events for the entire period. The performed study demonstrates that an increase in the speed and density of the solar wind coincided with the decrease in the Dst index in 58% cases (in 21 out of 36 geomagnetic storms). However, in some cases, there was a sharp simultaneous increase in both the speed and density of the solar wind that fell on the recovery phase of the storm. This also in most cases coincided with the sharp north-south fluctuations in the IMF Bz. These variations cannot be unconnected with the nature of the drivers of such geomagnetic storms. It is evident that the behavior of the solar wind speed during geomagnetic storm events can provide meaningful insight on the underlying mechanisms and processes that drive the geomagnetic storm.

This study investigates Pc5 pulsations during the St. Patrick’s Day geomagnetic storm of March 17, 2015, using ground-based magnetic data from the SER station in Chile (29.827° S, 71.261° W), satellite observations, and geomagnetic indices. Pc5 pulsations, with frequencies of 1.67–6.67 mHz, are influenced by various factors, including the Kelvin–Helmholtz instability, field line resonance effects, and solar wind dynamics. During this storm ignificant variations in solar wind parameters were observed, with positive correlations between Pc5 pulsations and parameters like temperature, density, speed, and pressure, especially during the main and recovery phases Pc5 pulsations exhibited large amplitudes during the storm, potentially driven by magnetospheric MHD waveguide/cavity mode and induced by the substantial compression of the geomagnetic field from the solar wind. Our results show the appearance of Pc5 pulsations at low latitudes and strong correlations between solar wind parameters and Pc5 signals during all storm phases, with maximum correlation coefficients of 0.98.

The article considers the period from September 4 to September 10, 2017, inclusive, during which the last proton events of solar cycle 24 occurred. In order to detect possible additional proton sources and verify the sources already listed in various catalogs, we apply an empirical method for predicting proton events to all solar flares detected during this period. It is based on the threshold criteria of the parent flares. In addition, we apply an algorithm for automatic search of proton flares obtained by machine learning. Two variants of the automatic search algorithm are used: the first one (method 319) does not take into account the duration of the radio emission, while the second one (method 189) imposes a condition on its duration (>2 min). The empirical method shows that, except for the source flares found by the time of the first arrival of solar protons on Earth, other flares of this period do not fulfill all the criteria of “protonicity.” An additional test of the automatic method is the detection of proton flares that we selected by the protonicity criteria but that did not make it to the training sample. Method 319 considers proton flares X9.3 on September 6, 2017, M1.4 and X1.3 on September 7, 2017, and C8.3 on September 8, 2017, as proton flares. Method 189 does not consider the flares of September 7 and 8, 2017, as credible proton sources, which is consistent with expert empirical estimates of the protonicity criteria.

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.