Geomagnetism and Aeronomy

Abstract

Ground-based observations of cosmic rays by the spectrographic global survey method were used to study the ground-level enhancement in cosmic ray intensity on August 24, 2002. Spectra of variations of primary cosmic rays and their anisotropy were obtained. Based on measurements from the GOES spacecraft and global network of cosmic ray stations, the differential rigidity spectra of accelerated particles in the vicinity of the Sun were calculated. The maximum rigidity to which solar particles were accelerated was estimated.

Abstract

The paper presents the results of an analysis of observations of an eruptive prominence on the MFS and HSFA2 spectrographs of the Ondřejov Observatory (Astronomical Institute, Czech Republic) in the hydrogen, helium, and calcium lines. After spectral processing, the integral radiation fluxes in the lines were determined and the physical parameters of the plasma were calculated theoretically using a model in the absence of local thermodynamic equilibrium. Comparison of the observed and calculated values showed that the observed radiation fluxes in the lines can be explained in a model of stationary gas radiation taking into account the opacity in the spectral lines. To calculate the theoretical fluxes, in some cases, it was necessary to introduce radiation from several layers with different temperatures and heights. The calculated radiation fluxes agree with the observed ones to within 10%. As a result of the simulation, the main parameters of the plasma of the prominence were obtained: temperature, concentration, etc. The values of the radiation fluxes in the spectral lines are evidence of inhomogeneity of the emitting gas, and there may be regions next to each other with temperatures differing by an order of magnitude.

Abstract

The equilibrium conditions of a magnetic flux rope containing a prominence depend on the properties of the surrounding magnetic field of the corona and geometry of the flux rope itself. The eruption of a prominence is usually associated with a loss of stability in the external field upon reaching a height above which the field decay index exceeds the critical value for eruptive instability development. For flux ropes with an axis in the form of a straight line or a circle, the critical value of the field decay index is 1–1.5. By extrapolating the magnetic field in the corona from field measurements in the photosphere, it would be possible to predict the probability of eruption of a particular prominence. However, taking into account the fact that the ends of the magnetic flux rope are rooted in the photosphere and remain fixed because they are frozen in the photospheric plasma, significantly affects the critical value of the index and complicates the forecasting problem. If the magnetic flux rope retains the shape of a torus segment in its evolution, then the critical value of the field decay index for its vertex depends on what part of the torus it constitutes, being minimal for approximately half the torus and having a value significantly less than unity. How the eruption of a flux rope will develop after loss of equilibrium also depends on what part of the complete torus it constitutes at the time of onset of eruption. Shorter flux ropes are accelerated very energetically, but briefly, generating stronger electric induction fields that trigger flare processes. However, the terminal velocity that a short flux rope can achieve during acceleration is less than that of longer ropes that accelerate less intensely but for a longer time. The induction effects of the latter are less pronounced, so that they are capable of producing only weak flarelike manifestations. Thus, the eruption of a short prominence, which has gained a relatively low velocity, can be stopped at a certain height in the corona without generating a coronal mass ejection, but such a “failed eruption” contributes to the development of flare phenomena. Conversely, eruptions of long prominences more often lead to coronal mass ejections and weak flare manifestations.

Abstract

A model of the main geomagnetic field for 2020 and a model of secular field variations up to 2025 have been constructed from measurements from SWARM satellites. These models have been included in International Geomagnetic Reference Field model IGRF-13. The methodology for data selection and model calculation is described.

Abstract

The study analyzes the long-term average annual OH* temperature trend, the values of which were obtained from nighttime spectral measurements of hydroxyl airglow bands at Zvenigorod research station (56° N, 37° E) from 1957 to 2022. At present, this OH* temperature series, which reflects the thermal state of the mesopause region, is the longest in the world. On its basis, the linear trend and response of temperature to changes in solar activity are estimated both in general for the entire data set and for individual time intervals. In the first case, the trend was –0.23 ± 0.04 K/year. In the second case, the analysis showed a strong cooling in the mesopause region (–0.53 ± 0.34 K/yr) until the 1970s, which subsequently slowed to –0.14 ± 0.03 K/yr. Comparison of the results with other measurements and model calculations shows that the latter have lower trend values. It is suggested that the causes of the temperature trend, in addition to the increase in greenhouse gases, the main one being CO2, can be due to long-term changes in the dynamics of the upper atmosphere.

Abstract

The behavior of the main parameters of the interplanetary medium, cosmic ray variations, and geomagnetic activity as magnetic clouds pass the Earth (466 events from 1967 to 2021) was studied. Time distributions of these parameters during magnetic clouds passage are considered. It is shown that the maximum values of the solar wind velocity, interplanetary magnetic field strength, and geomagnetic activity indices are more often recorded in the front part of the magnetic cloud, while the minimum values of the temperature index, density, and equatorial component of cosmic ray anisotropy can be observed in any part of the studied structure.

Abstract

Disturbances in the lower ionosphere and in the region of the maximum of the ionospheric F2 layer during the eruption of Shiveluch volcano in April 2023 are analyzed based on data from ground-based magnetometers and GPS radio sounding of the ionosphere. The magnetic stations were located at distances of 455 (Paratunka) and 752 km (Magadan) from the volcano. The variations in the magnetic field and total electron content of the ionosphere were studied as characteristics of the ionospheric response to this event. Analysis of the measurements showed that the ionosphere was impacted by seismic Rayleigh waves and atmospheric acoustic-gravity waves generated by volcanic explosions. The energy of several explosions was estimated from the amplitude of the ionospheric signal in the total electron content.

Abstract

Tsallis nonextensive statistical mechanics (or q-statistics) has been used for the first time to study pulsating auroras, which are regularly observed in the auroral ionosphere during geomagnetic disturbances. For systems in which long-range interactions, such as ionized gas or plasma, take place and whose dynamics are determined primarily by long-range electromagnetic forces, it can be expected that nonadditive and nonextensive thermostatistic principles can characterize their macroscopic behavior. In this paper, we argued that pulsating auroras exhibit nonextensive properties and can be described, among other things, by q-statistics. We have also demonstrated that the non-extensive parameter q correlates well with the flatness index and with the scaling index, which indicates the applicability of this approach for auroral glow. Thus, q-statistics can be used to analyze phenomena in the high-latitude region of the Earth.

Abstract

The parameters of dimmings and their relation to coronal mass ejections (CMEs) are studied to determine the location of possible sources of ejections on the solar disk during solar cycle 24. We used the Solar Demon database, which contains information on flares and dimmings obtained by processing images from the SDO/AIA space observatory. Of all the analyzed dimmings, 16% are аssociated with CMEs from the CACTus database using SOHO/LASCO coronagraph data for 2010–2018. Based on the parameter distribution, it is found that dimmings related with CMEs are on average events with large absolute parameter values. The correlation coefficient between the position angle of the dimmings and the position angle of the CME associated with them is 0.96. For dimmings observed in the central part of the solar disk, we obtained correlation coefficients between the CME velocity and dimming parameters that are close to 0.5. The results can be used to model the propagation of CMEs and to refine the probability of their arrival to the near-Earth orbit.

Abstract

An experiment was performed on using advanced macroscopic nonlocal correlations to forecast slow random oscillations of the Dst index of geomagnetic activity. The global maximum of the correlation of Dst with the electrode detector signal reaches 0.97, which is sufficient for forecasting, and its time shift corresponds to advance of the detector signal relative to Dst for 329 days. The large magnitude of the time shift is due to the slow diffusion mechanism of entanglement swapping between the detector and the source. In this case, the position of the global maximum of the correlation function coincides with the position of the global minimum of the entropy independence function, which confirms that it is not distorted by possible nonlinearity of the relationship and determines the optimal lead time of the forecast. Long series of test Dst forecasts have been calculated based on data from a nonlocal correlation detector with a fixed lead time using three methods: current regression, current impulse transient response, and current neural network. The forecast accuracy is sufficient for all practical purposes.

Abstract

For northeastern Eurasia (60°–70° N, 90°–180° E), the bottom depth of the lithospheric magnetoactive layer is estimated using the centroid method based on two-dimensional spectral analysis of the lithospheric magnetic field. The lithospheric magnetic field within the study region is described by the EMAG2v3 global model. The results show that maximum values (>50 km) of the depth to the bottom of lithospheric magnetic sources are observed almost everywhere under the Siberian Platform north of 65° N. Minimum depth values (<30 km) are traced under the Koryak–Kamchatka fold belt and the Okhotsk–Chukotka volcanic belt. Under the Verkhoyansk–Kolyma fold belt, different maxima (up to 44 km) and minima (up to 30 km) of the bottom depth are seen. Assuming that magnetite is a main magnetic mineral in the continental lithosphere, our distribution of the bottom depth indicates eastward lithospheric heating, from the Siberian Platform to the Koryak–Kamchatka fold belt. The revealed tendency is confirmed by independent geophysical data. Comparison of the results with the distribution of epicenters of regional earthquakes (M ≥ 4.0, 1962–2020) shows that most sources of strong earthquakes (M ≥ 6.0) recorded during the instrumental period of observation, are confined to zones in which a sharp change in depth to the bottom of lithospheric magnetic sources occurs.

Abstract

Activity in a prebreakup auroral arc in the form of vortexlike structures, the appearance/disappearance of which is preceded by an increase/decrease in the brightness of the arc, was studied in the context of a magnetospheric substorm, large-scale ionospheric convection, the situation in the interplanetary medium, and triangulation measurements of the arc height. The structures are observed in the premidnight hours and represent a superposition of two auroral forms: a large-scale bend in the arc that outlines the polar boundary of the diffuse auroras and smaller luminous tongues of luminosity (mini-torches) elongated along the convection on the western slope of the bends. The structures as a whole move against convection, towards substorm activity to the east of the observation area. We attribute the appearance of structures to the propagation of a disturbance deep into the magnetosphere, generated as a result of interaction of the magnetopause with a solar wind inhomogeneity, on the front of which Bz turns southward. The results of triangulation measurements show that the increase in brightness in the prebreakup arc shortly before the appearance of vortexlike structures is accompanied by a decrease in the height of the lower edge of the arc, which we explain by the appearance of a parallel electric field above the arc, which accelerates the precipitating electrons. The role of such a field in the formation of the torchlike structures is discussed in the framework of the interchange instability of the pole boundary of diffuse auroras.

Abstract

The results of correlation analysis of radon and air ion concentrations based on measurement data in an underground laboratory are presented. For pairs of pressure–radon and pressure–ion variables, a delayed pumping effect was revealed, similar to that previously observed for neutrons and gamma rays. A simple phenomenological model is presented to explain the results obtained. Within this model, the delay is caused by the gradual accumulation of radon in the room as atmospheric pressure decreases. The balance of the accumulation rate of radon, the time of its radioactive decay, and the characteristic time of pressure variations leads to an effective delay of 2 days between variations in atmospheric pressure and radon concentration. Correlation analysis for pressure–ion variables indicates that the air carrying radon into the laboratory already contains ions formed in soil pores. These ions make up approximately 21% of the total ions in the laboratory.

Abstract

The article investigates the statistical relations between the values of geomagnetic indices and the characteristics of cosmic rays and interplanetary disturbances for Forbush decreases with a sudden and gradual commencement associated with different types of solar sources: (a) coronal mass ejections from active regions accompanied by solar flares; (b) filament eruptions outside active regions; (c) high-speed streams from coronal holes; and (d) multiple sources. Using statistical methods, we also compare the dependence of geomagnetic indices on cosmic ray and solar wind parameters for Forbush decreases in solar cycles 23 and 24. The results show that (a) interplanetary disturbances associated with coronal mass ejections from active regions cause mainly magnetic storms with a sudden commencement, (b) interplanetary disturbances associated with high-speed streams from coronal holes cause mainly storms with a gradual commencement, and (c) interplanetary disturbances associated with filament eruptions outside active regions cause equally likely storms with a sudden and gradual commencement. For sporadic Forbush decreases, the cosmic ray and geomagnetic activity parameters are, on average, larger for sudden commencement events; for recurrent Forbush decreases, the nature of the event commencement does not affect the magnitude of these parameters. For all types of solar sources, the disturbed solar wind parameters are, on average, larger in events with sudden commencement. The geoeffectiveness of interplanetary disturbances is significantly higher in cycle 23 for events associated with ejections from active regions; for other types of disturbances, the difference between cycles is weak.

Abstract

Based on the global empirical model of the median of the critical frequency of the F2 layer (SDMF2), the properties of diurnal variations in the annual asymmetry in the maximal concentration NmF2 of the F2 layer for different values of the solar activity index F are analyzed. The AI index characterizing the relative difference in NmF2 averaged over all latitudes and longitudes between January and July at a given local time is used as a parameter of this asymmetry. It is found that a semidiurnal mode prevails in the diurnal variations in the AI index with maxima at the daytime and nighttime hours. The daytime maximum of the AI index hardly depends at all on the solar activity level. The nighttime AI maximum decreases with an increase in solar activity. The daytime and nighttime maxima in AI almost coincide by the amplitude when AI = 16–17% for low solar activity. The difference in the solar radio emission flux between January and July due to the ellipticity of Earth’s orbit relative to the Sun contributes substantially into the AI index at all hours of the day. On average, it is 3–4% and could reach 5% for low solar activity during the nighttime hours. The difference in the AI index for low and high solar activity according to the International Reference Ionosphere model IRI (with the URSI and even more with the CCIR coefficients) is overestimated with respect to the SDMF2 model at almost all hours of the day, apparently due to limited amount of the experimental data used to obtain the CCIR and URSI coefficients, especially over oceans.