Geomagnetism and Aeronomy最新文献

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.

In the present paper, a long period of GPS-TEC observed at Agra station, India has been investigated to develop a support vector machine (SVM)-based model corresponding to earthquakes that occurred around Agra within 2000 km from 2010 to 2013. The different datasets are prepared with the help of the GPS‑TEC data, solar activity (R and F10.7 cm), magnetic storm (Dst and ∑Kp indices) parameters, etc. for the magnitude in the range of 4–7.7 at the interval of 0.5 and outer radius of 2000 km at the interval of 500 km. Here, 90% of the data is used for training, and the rest of the 10% of data is used for test purposes. These parameters are used as the input in the Linear and Medium Gaussian SVM models, respectively. The confusion matrices are obtained for each dataset and then skill scores such as precision, recall, and accuracy are calculated, statistically. The best results of skill scores are obtained in the case of magnitude range 4–7.7 and the outer radius of 2000 km. The receiver output characteristics (ROC) curves are plotted and the maximum accuracy of 94% is obtained. A k-fold cross-validation (k = 5) technique is used to validate our models. Further, both models are compared by using the Wilcoxon signed-rank test. Bayesian Optimizer optimizes the GPS-TEC datasets. Finally, these models may be utilized for real-time data classification.

Recently, Samara et al. (2022) showed that proportionality between the solar fast wind velocity V from the low latitude coronal holes (CH) and their area S_ch is satisfied only for small-sized CH, while the saturation effect for larger CH is revealed; i.e., a plateau is formed in a V(S_ch) plot. This is explained by the geometric complexity of CH, described by the fractal dimension. Previously, Akhtemov and Tsap (2018, 2019) established that the correlation coefficient between V and S_ch reaches a maximum for a CH located within a fractional area ±10° in longitude and ±40° in latitude. They suggested that this inference is related to the radial propagation of the solar wind and, hence, the increasing of S_ch should not be accompanied by an increase of V for large CH. The presented work provides a detailed comparative analysis of the results obtained by Samara et al. (2022) and Akhtemov and Tsap (2018, 2019). Arguments are given in favor of the model related to the saturation effect with the radial propagation of the fast solar wind.

This paper investigates the features of the generation of fast and slow MHD shock waves in the lower layers of the solar corona. An analytical solution is obtained at the shock front for both types of shock waves and it is shown that the primary role in the formation of anomalous heating belongs to weak MHD shock waves, which do not have a lower speed limit for generation in the upper layers of the solar chromosphere.

The decisive role of the neutral component of solar plasma in the dissipation of electric currents in magnetic flux tubes is shown. For the first time, the dependences of the Cowling resistivity and the rate of the Joule dissipation were obtained for various current magnitudes in a wide range of heights, from the photosphere to the corona. Based on the atmospheric model of Avrett and Loeser (2008) it was shown that the Cowling resistivity exceeds the classical (Spitzer) resistivity in the chromosphere and the transition region. The Spitzer resistivity prevails over the Cowling one at the altitudes less than 300–1000 km depending on the electric current magnitude. The Cowling resistivity plays the main role at the electric currents of more than 10⁹ A in the corona with a relative density of neutral atoms ∼10^–7. It was found that the maximum of the Joule dissipation is located at the altitude of about 2100 km, which creates favorable conditions for formation of the chromosphere-corona transition region and heating of the corona. Anomalous (turbulent) resistance requires a lot of tiny current filaments in a flux tube. The role of Joule dissipation in the heating of pre-flare plasma and in the formation of the sunspot light bridges is discussed.

The subject of this study is the effect of space weather on the processes of interaction between Earth’s lithosphere, ionosphere, and atmosphere. Evidence is provided that solar flares in the short-wavelength region of the electromagnetic spectrum destabilize of the electric field between the ionosphere and upper lithosphere, leading in some cases to the triggering of powerful volcanic and seismic phenomena during periods of high solar activity. Conversely, an increased background flux of galactic cosmic rays (GCR) during low solar activity leads to a decrease in the critical level of stresses preceding powerful tectonic events and contributes to an increase in their frequency. The studied interactions influence the formation processes and dynamics of aerosols, which in turn influence cloud formation and climate change.

In the paper, we present an analysis of the parameters of type III radio bursts registered in the range of 50–500 MHz by the Solar Spectropolarimeter of Meter Range (SSMD) of the radio astrophysical observatory of the Institute of Solar-Terrestrial Physics, Siberian Branch, Russian Academy of Sciences during the period of solar activity minimum from 2016 to 2019. In the study, an original method for identifying type III radio bursts has been developed and used with allowance for the features of the data related to the time and spectral resolution of the device. Most of the studied events are associated with B-class flares according to the GOES classification and lower. However, the distribution of events according to the velocities of the electrons generated the radio bursts emission does not differ from the standard distribution, including for powerful flares. A general tendency for an increase in the duration of a radio burst with a decrease in the energy of the electrons that generated it has been revealed. The electron energy band width is about one order of magnitude. The events of 2017 associated with powerful flares are at the upper limit of the energies of this band.

The methods proposed earlier by the authors to extrapolate the positions of coronal mass ejections (CMEs) to the propagation times from the beginning to the escape into interplanetary space by the SOHO/LASCO coronagraph data have been used. This makes it possible to obtain the CME kinematic parameters needed to refine the solar proton acceleration model for the events of February 17, 24–25, and 28 and July 16–17, 2023 (the most significant proton events of the ascending phase of solar cycle 25). For proton flares on the visible disk of the Sun, it is found that CMEs should have started to accelerate before the selected zero time (heating of the flare plasma to 12 MK (GOES), electron acceleration greater than 100 keV, and the onset of nonthermal emission (ACS SPI, RSTN). Particle and CME accelerations continue at least during the active phase of the flare (T > 12 MK). Evidence has been obtained for the sequential acceleration of two CMEs, slow and fast, in the event of February 25, 2023, when the second CME caught up with the first and engulfed it (“cannibalism”).

Based on the available photometric data for the star V647 Her, including those obtained from photographic archives, we considered the yearly-mean brightness variability over the time interval 1939–2022. The dense data series obtained in 2019 and 2022 at CrAO as well as the sample for 2004 from the SuperWASP catalog showed changes in light curves and in color indices of the star with a period of 20.69 days. Changes in the V–I color index indicate the presence of cool spots on its surface. The parameters of starspots were calculated within the zonal model for each year and it was found that the temperature of the spots is 500–600 K lower than the temperature of the quiet photosphere with T_eff = 3300 K, the spots occupy from 8 to 30% of the entire surface of the star in different years. The spottedness of the star’s photosphere is an indicator of its activity, and according to the interval between the epochs of minimum spottedness, we derived a characteristic time between the minima in activity of V647 Her of about 60 years, and the duration of the maximum of activity of about 5 years.

We examined pre-flare brightenings in ultraviolet (UV) and X-ray emissions during flares on September 23, 2014, and January 11, 2013. We analyzed UV maps at nine wavelengths based on SDO/AIA data and RHESSI X-ray images over a one-hour interval before the onset of the flare. We obtained the temperature and emission measure dependencies of the quasi-thermal X-ray emission during the precursor periods. The plasma temperature in the precursor regions exceeded 1 MK. The emission in the extreme UV (EUV) lines was used to identify the filamentary structure. The SDO/HMI vector magnetic field data allows the reconstruction of the magnetic field pattern in the coronal part of the filaments using the NLFFF method. We found magnetic field structures containing flux ropes during the precursor phase. We discuss the role of magnetic flux ropes, their temporal evolution in the dynamics of the pre-flare stage, and the transition from the precursor to the explosive phase of the flares. We conclude that there is a causal relationship between the precursors of the flares on September 23, 2014, and January 11, 2013, and the events themselves.