Geomagnetism and Aeronomy最新文献

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”).

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.

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.

Determining the speed of the solar wind emanating from coronal holes near the Sun is a key problem for modeling plasma parameters throughout the heliosphere. Plasma temperature and density, in addition to speed, are the input parameters to global magnetohydrodynamics models, but the estimated temperature and density boundary conditions are calculated from the simulated solar wind speed. In this study, we analyzed how long-term variations in the properties of open magnetic field sources modeled from different series of magnetograph observations are related to the plasma parameters measured by satellite. The analysis also considers coronal holes based on SDO/AIA 193 Å and solar wind speed observations in the Wang-Sheeley-Arge approximation (WSA). We found that during the period 2015–2023, the areas of equatorial coronal holes correlate better with the observed solar wind speed than the results of WSA simulations. Among the three considered series of magnetographic observations (STOP, SDO/HMI, GONG), during the period of minimum solar activity, calculations based on STOP data perform better.

In the paper, we examine the α inclination of the magnetic field of sunspots relative to the vertical. To determine the deviation angle α, a method to search for differences in the maximum of the longitudinal component of the magnetic field at various distances of spots from the central meridian in the eastern and western hemispheres of the Sun was used. Particular attention has been paid to the difference in the angles α for spots of leading and tail polarity of the magnetic field. Deviation angles α were shown to depend on the logarithm of the area while the dependences have opposite signs: α_L = 0.45°(±0.5) + 2.085°(±0.5) log S, (r = 0.95) for nuclei of leading polarity spots (L) and α_T = 5.43°(±1.0) – 3.95°(±0.7) log S, (r = 0.93) for nuclei of tail polarity (T). Here, the deviation of magnetic fields to the western limb is taken as a positive value. The found dependencies indicate the ascent of U-shaped force tubes.

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.

The structure of the quasi-perpendicular bow shock of the Earth observed by the MMS spacecraft on 31 January 2017 with an Alfvén Mach number of approximately 10 and plasma parameter β of approximately 3, has been simulated using the Maximus hybrid kinetic code. We investigated types of instabilities governing the front structure and showed that in this case both ion Weibel and Alfvén ion cyclotron instabilities can arise at the shock foot simultaneously, thus leading to fast magnetic oscillations with a relative variation close to unity. Some signatures of the mirror instability were found in the near downstream. Simulation also showed that the front structure substantially differ for shock inclination angles of 50° and 75°.

The maximum energy of a solar flare is found using a model of particle acceleration in a magnetic X-singularity. Based on a comparison of this model with observed extreme events, it was determined that flares with the highest possible energy have already been observed. These include events of 1859, 1940, 2003, which had an X-ray class of X40 ± 5 (according to the GOES classification). In this case, the maximum flare energy in the modern era does not exceed 5 × 10³² erg, and such powerful flares occur at intervals of about 70 years.