Geomagnetism and Aeronomy

Abstract

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.

Abstract

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.

Abstract

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.

Abstract

In this paper, we studied the impact of solar activity, especially proton density, He++/H+ ratio and temperature of solar wind, on the geomagnetic field and thereby on earth’s climate. The verified data of these indices are collected from the official websites: wdc.kugi.kyoto-u.ac.jp and www.srl.caltech.edu/ace. Using the data values, both the indices are analyzed and studied to explore the link between solar activity and geomagnetic field. The magnetic field is irregular with negative and positive peaks and at the same time it shows the uniformity with the irregularities of solar wind plasma parameters. It has been observed that solar wind plasma has a significant influence on the intensity of magnetic field of earth and this correlation can be used for weather forecasts and climatic studies in the future.

Abstract

This study investigates the vertical electron content (VTEC) variations and depletions using two years of Global Positioning System (GPS), Total Electron Content (TEC) data from 2012 and 2013. The data, gathered at altitudes between 5° and 15° and longitudes between 34° and 48°, was specifically focused on quiet days and analyzed from nine GPS stations. Employing a spherical model and standard kriging interpolation techniques, the research explored hourly, diurnal, and seasonal fluctuations of VTEC over the two-year period. The spherical model demonstrated high efficacy in estimating data with short lag distances, effectively capturing hourly and daily VTEC fluctuations. Diurnal VTEC variations showed a consistent pattern: increasing from dawn, peaking at 1200 UT, and declining to a minimum after 1800 UT. The peak in diurnal variation was most pronounced at Debark, with similar patterns observed at other stations, reflecting consistent ionospheric behaviors due to geomagnetic conjugcy. A strong correlation was observed between the alignment of the solar terminator and magnetic meridian during equinox seasons and VTEC variation and depletion, with the most significant effects during equinoctial seasons. The study identified a distinct north-south gradient in VTEC within the region, with levels exceeding 65 TECU in the north and around 40 TECU in the south, depending on ionospheric conditions. Nighttime VTEC levels typically decreased to approximately 5 TECU. The spatial distribution analysis of TEC revealed a pronounced maximum concentration in the northeastern sector, contrasting with a minimal concentration in the southwestern sector. This research provides valuable insights into the spatial and temporal behaviors of VTEC, enhancing our understanding of ionospheric dynamics within the specified region.

Abstract

Fractal analysis of VLF electric field data obtained by using vertical antenna located at Chaumuhan, Mathura station (Lat., 27.5° N, Long., 72.68° E) has been carried out using Higuchi method for investigating the impact of moderate shallow earthquakes (M = 4.9–5.6, depth 4.44–16.7 Km) that occurred during February 1, 2016 to October 31, 2016 (excluding April 2016) on the fractal dimension of VLF data. The results of the analysis show that daily values of fractal dimension vary much above and below the monthly mean during the period of observations, 1–30 days before and 1–30 days after the onset of the quakes considered in the present study. The ranges of reductions and enhancements in fractal dimension from the monthly mean are 0.05–0.33 and 0.054–0.43 respectively while the percentage ranges of reductions and enhancements in its daily variation are 3.0–23.21 and 2.81–19.88% respectively. The observed variations in fractal dimension have also been studied in the light of other expected sources like, magnetic storms, lightning activity, local building noises, and instrumental errors which may affect the fractal dimension of the VLF data. It is noticed that the observed variations of fractal dimensions do not correspond to these spurious sources considered. Further, model describing the genesis of VLF emissions in preparatory zones of the impending seismic events and their mechanism of transmission to the observing station have also been discussed.

Abstract

Satellite navigation systems are used for positioning purposes, however to calculate an accurate position, it is crucial to take into account all possible sources of error. The Ionosphere is the primary cause of the positional error. There is a lot of research into first-order ionospheric error estimation and removal. Due to the growing demand for positioning precision across a wide range of applications, significant research has been done over the last two decades to ascertain the impact of second-order ionospheric error (SOIE). However, very less research has been identified that examines the relationship between SOIE and the receiver’s geographic location and total electron content (TEC). Achieving the desired millimeter/centimeter level positional accuracy in these regions requires the study of a realistic diurnal and seasonal variability of SOIE because the behavior of ionospheric TEC in equatorial and low-latitude regions (Indian region in this case) is highly dynamic. Additionally, NavIC (Navigation with Indian Constellation), an Indian satellite navigation system, uses carrier frequencies, namely L5 and new frequency S1, as opposed to GPS L1 and L2, which presents a fresh chance to investigate the effects of SOIE on these frequencies. This research may serve as a benchmark for systems like NavIC that are using L5 and new S-band frequencies for satellite signal transmission, space weather monitoring, and ionosphere abnormalities research. To comprehend various elements of its seasonal properties, this research estimates and analyses SOIE. Data from the SOIE were examined for 12 months, from May 2018 to February 2019, to analyze the diurnal and seasonal fluctuation. It has been noted that seasonal and diurnal fluctuations have a substantial impact on the SOIE. In comparison to the winter months, the SOIE levels are higher in the summer and equinoctial months. Although the SOIE peak levels are similar during the equinoctial and summer months, a higher midnight value and a slowly declining rate have been noted. At L5 frequency, there is a significant seasonal fluctuation in SOIE (–1.1 to –2.84 cm), whereas at S1 shows just a little seasonal variation (–0.1 to –0.3 cm) throughout the year. Additionally, geostationary orbit (GEO) satellites are discovered to be more suitable for the analysis of SOIE than satellites in geosynchronous orbit (GSO), and they might also be employed for ionospheric studies.

Abstract

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: αL = 0.45°(±0.5) + 2.085°(±0.5) log S, (r = 0.95) for nuclei of leading polarity spots (L) and αT = 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.

Abstract

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 Sch 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(Sch) 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 Sch 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 Sch 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.

Abstract

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.

Abstract

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.

Abstract

A reconstruction of the average monthly values of sunspot areas—the physical index of solar activity—is proposed. The uncertainty of the obtained values for a significance level \(\alpha = 0.05\) is estimated. The duration of the number of monthly means has become 275 years. It is shown that the AR index, when used in reconstructions of solar activity of historical observations with small telescopes, is more advantageous than the indices of the number of spots or groups thereof. This index is not sensitive to the possible loss of small groups, which on average make up about a third of the overall number.

Abstract

The cause of the asymmetry in the sunspot distribution in the northern and southern hemispheres of the Sun at the end of the Maunder Minimum is studied. It is demonstrated that the expected asymmetry of generation sources is insufficient for such an explanation. To study the influence of asymmetry of generation sources, numerical simulation is used, based on modifications to the Parker model.

Abstract

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.

Abstract

The results of analyzing the relationship between large-scale epidemics (pandemics) caused by the Ebola, influenza AH1N1, and AH7N9 viruses and the MERS-CoV coronavirus with global solar factors for the period from 2008 to 2019 (24th cycle of solar activity) are presented. A variable change in the annual values of pandemic cases has been established, corresponding to the regular course of F10.7 cm (r ~ 0.65), MF (r ~ 0.85) and λ315 nm (r ~ 0.83) in the 24th SA cycle. It was concluded that the dynamics of the spread of pandemics depend on temporary changes in UVB radiation power, in particular, at the boundary of the spectral bactericidal efficiency curve (λ315 nm).

Abstract

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.

Abstract

In the recent work by Usoskin et al. (2021) a series of annual sunspot indices for the years 971 to 1899 was reconstructed. Using this series, we study behavior of the “length-amplidude rule” (LAR), according to which the mininum-to-minimum length of a given 11-year solar cycle anticorrelates with the amplitude of the next one. We show that approximately since the 14th century two regimes exist in the series: I) epochs of normal activity, when the LAR is observed; II) epochs of the Maunder, Spörer and Wolf grand minima, when there were no significant links between the amplitudes and lengths of the 11-year cycles. Before the 14th century the LAR and its relation to the level of global activity of the Sun is less pronounced, which, probably, is a consequence of inaccuracies of the 11-year cycle parameters determination in this epoch.

Abstract

For the first time, several flare events are analyzed based on multifrequency observations using the Radio Solar Telescope Network. The purpose of the analysis is to identify signs of flare preparation. In all considered cases, preflare quasi-periodic fluctuations (QPFs) of radio emission were detected. The duration of preflare wavetrains is 6–20 min. Wavetrains consist of 3–5 pulses. QPFs at lower frequencies (200–600 MHz) begin later than those at high frequencies by 2–6 min. QPFs at frequencies of 2695–8800 MHz occur almost synchronously. The highest amplitude of QPFs is observed at a frequency of 4995 MHz. The observed QPFs can be explained by the force-free magnetic rope model (Solov’ev and Kirichek, 2023).

Abstract

The results of observations of coronal jets on the Sun are briefly reviewed. Data on jets of different types (jets, jetlets) were collected. Their properties are considered, such as lifetime, length, width, velocities, coupling to the magnetic field, and their putative role in hot plasma and energy transfer into the corona. Observational data obtained with ground-based and space telescopes were used. There is growing evidence that jets play a key role in imparting mass to the corona and solar wind and can provide sufficient energy to power the solar wind (see, e.g., (Tian et al., 2014)). Modern observations by the Parker Solar Probe and Solar Orbiter spacecraft will contribute to the understanding of solar jets and related phenomena.

Abstract

The paper studies the dynamics of high-temperature structures (with a temperature of T ≥ 10 MK) in the corona above active regions (ARs) in quiet temporal intervals, before solar flares of high X-ray classes and during and after individual flare events, and determines the role of electric currents in heating the coronal plasma. In the study, we used data from the Solar Dynamics Observatory (SDO) spacecraft: magnetograms obtained by the Helioseismic and Magnetic Imager (HMI) instrument (used to detect and calculate the magnitude of large-scale electric current) and photoheliograms of the solar corona in ultraviolet radiation 94, 131, 171, 193, 211, and 335 Å channels of the Atmospheric Imaging Assembly (AIA/SDO) instrument (used to construct maps of temperature distribution in the corona above the AR, detect high-temperature structures, and study their evolution). The objects of the study were ARs NOAA 12 192 (October 2014) and 12 371 (June 2015) of the 24th solar activity cycle, which have high absolute values of large-scale electric current. The following results were obtained: (1) The discovered high-temperature structures represent a channel of large-scale electric current at coronal heights. (2) High-temperature structures in the corona above the studied ARs exist over a long (several days) time interval, which indicates the presence of a constant source of plasma heating; the temperature of the structures, the area they occupy, and their spatial orientation change over time. (3) High-temperature structures in the corona consist of individual elements with a cross section of ~108 cm. (4) Several hours before the X-ray flares of classes M and X datected in the studied ARs during their monitoring time, a significant decrease in the area occupied by high-temperature structures was observed, and in some cases, a decrease in temperature to 3–5 MK, which indicates a change in the physical conditions in the corona before powerful flares.