Geomagnetism and Aeronomy最新文献

Taking into account the real magnetic field geometry of Earth in the northern hemisphere, this work produced the equations of real diffusion coefficients for the ionospheric F region (390, 410, 450, 500, 550, 600 km) at low latitudes. In a steady state, diffusion coefficients show real values, while in an unstable state, they show complex values with real and imaginary components. We performed numerical calculations at F region altitudes within the ionospheric plasma to determine the diffusion coefficients for both cases. The results show that in the steady state, the diffusion coefficients have values that are very close to the speed of light. In unstable conditions, on the other hand, the real parts are generally close to the conductivity values, while the imaginary parts are similar to the sound speed magnitudes. The fundamental focus of this technique is to demonstrate and calculate the complex structure of diffusion coefficients in the ionosphere, representing the first such instance in the literature.

Ground-based electron density measurements from ionosondes are used to evaluate the accuracy of ionospheric empirical models, such as the International Reference Ionosphere (IRI) and the NeQuick models. In the present study, the results obtained from ionosonde and empirical models (NeQuick2, IRI2016, and IRI2020) of the electron density at the Addis Ababa, Ethiopia ionosonde station, with a geographic latitude of 9.03° N and longitude 38.76° E on selected days in 2014 are presented. In the comparison of the NeQuick2, IRI2016, and IRI2020 models with the ionosonde data, the percentage deviation and the correlation coefficient (R) are used as measures of the performance of the models. The overall results show that the latest version of the IRI2020 model outperforms NeQuick2 and IRI2016 in ionospheric electron density value, with NeQuick2 showing slightly better performance than IRI2016. Mostly, the NeQuick2, IRI2016, and IRI2020 models show overestimation of the electron density values from the ionosonde data. The NeQuick2 model overestimates with a maximum percentage deviation of 38%; the IRI2016 model overestimates with a maximum percentage deviation of 40%; and the IRI2020 model overestimates with a maximum percentage deviation of 30% from the ionosonde data measurements, while underestimating with percentage deviations of 10, 18, and 9%, respectively. The average values of the correlation coefficients of the NeQuick2, IRI2016, and IRI2020 models are 0.79, 0.74, and 0.81, respectively.

While the link between coronal mass ejections (CMEs) and geomagnetic storms has been well established, the prediction of intensity and forecasting of the storms are necessary to notify the adverse effects in advance. In this work, we explore the relationship of the intensity of geomagnetic storm (Dst index) and southward magnetic component (B_s) with the magnetic parameters of the source active region (Space-weather HMI Active Region Patch, SHARP parameters) during 2011‒2017 to find the connection between the magnetic parameters of the source active region and geo-effectiveness. A set of 31 halo CMEs is found to have produced geomagnetic storms from 2011 to 2017. The preliminary analysis shows that these events erupted from active regions with strong and complex magnetic field structures and found to be associated with weak to intense storms (‒6 to ‒223 nT). The following important results are obtained from the detailed analysis: (i) Most of the storms are caused from the events near disk center to western longitudes except three. (ii) Moderate correlations are found between some magnetic parameters of the source active region with the intensity of the storm and southward magnetic field component. (iii) Empirical relations are derived for storm intensity and southward magnetic component in terms of important source region magnetic parameters. Furthermore, we got good correlation for the product of speeds of interplanetary coronal mass ejection (V_ICME) and B_s with the Dst index. These findings reveal the Sun–Earth connection of certain events and give some clues on improving our ability to connect the intensity of geomagnetic storms with CME kinematics and source region magnetic parameters.

Satellite communication and navigation systems are increasingly essential in modern society, making it crucial to understand the impact of solar activity on these technologies. Total electron content (TEC) significantly influences satellite performance, necessitating accurate forecasting to maintain operational reliability. This research focuses on predicting TEC during eleven distinct X-class solar flares that occurred in February, March, May, June, and August 2024, utilizing a long short-term memory (LSTM) model. The study employs a comprehensive dataset of TEC data sourced from the IONOLAB database, alongside important solar and geomagnetic parameters such as Kp, Ap, SSN, and F10.7 obtained from NASA OmniWeb. The model’s predictive performance was validated against the IRI-2017 model. Results demonstrate that the LSTM model effectively captures TEC variations during periods of extreme solar activity, consistently outperforming the IRI-2017 model. For instance, during significant solar events, the LSTM model achieved notable performance metrics, indicating its capability to provide precise TEC forecasts. This research contributes to the advancement of space weather forecasting models, enhancing the reliability of satellite-dependent systems critical for global communication and navigation.

Measurement instruments onboard satellites are susceptible to various disturbances that can affect not only the accuracy of the measurements but also the entire satellite mission. Of particular concern are disturbances associated with Earth’s magnetic field, which arise when field lines intercept the spacecraft (S/C) body or one of the Langmuir probes dedicated to measuring electric field disturbances, as is the case for the Demeter satellite. We analyze this effect for a Langmuir double probe, which provides ambient electric field measurements on low-orbit satellites with altitudes of approximately 650 km. The electric field disturbances arise when the sheath surrounding at least one of the probes is connected to the S/C body and/or solar panel through a magnetic field line (also known as a tube of force). We found that for certain orbits, this disturbance can be significant in strength and can last approximately 10 min, regardless of whether the orbit is nighttime or daytime.

The behavior of the total electron content (TEC) on a global scale has been the subject of research for several years. However, certain features of this behavior, including the effectiveness of energetic particles and their anomalies at different latitudes, are poorly understood. This research reports a comparative analysis of the seasonal and daily changes in the TEC as observed from 2019 to 2021 (low solar activity) in the mid-latitudes between 33.1 and 40.1 degrees. The points include eight stations across four countries with the following coordinates: Tehran (Iran), Hamedan (Iran), Tabriz (Iran), Yerevan (Armenia), Diyarbakir (Turkey), Ankara (Turkey), Nicosia (Cyprus), and Baghdad (Iraq). Also, by taking the quiet solar activity conditions into account, TEC’s variations have been investigated hourly, daily, and seasonally. For this research, TEC observations from the Global Positioning System (GPS) have been analyzed. The results showed that the highest TEC values occurred during 0900–1100 UT (1300–1500 LT), and the lowest values occurred during 2400–0200 UT (400–600 LT). From a seasonal point of view, in 2019, the maximum value of TEC was observed during the March equinox, and the lowest maximum value of TEC was observed during the December solstice, but in 2020 and 2021 the maximum value of TEC was observed during the June solstice and September equinox, the lowest value of TEC is observed during the December solstice.

This article discusses the testing of the complexity of the instrumental series of Wolf numbers. The work is initiated by the hypothesis of the existence of a low-dimensional dynamo as a model of the Sun’s magnetic activity. This mechanism produces the observable, in the Takens sense, as a broadband chaotic signal with a dominant 11-year mode (Frick et al., 2022). The time series of Wolf numbers is claimed to be this signal. In this article, we consider two problems. In the first, we describe a method for obtaining the average cycle for the dominant 11-year mode. It is based on the Fisher–Rao metric and the quantum mechanical analog of “probability amplitudes” for cycles. In the second problem, we investigate the algorithmic complexity of the instrumental series of Wolf numbers (SSN2) compared with surrogate data obtained by fractal mixing of this series. The mixing “whitens” the 11-year cycle but retains tuples of 2–3 monthly mean counts. Complexity was estimated as permutation entropy (Bandt et al., 2002). It was hypothesized that if the dominant mode was chaotic in nature, the complexity of the source and surrogate series would be close. Our results do not contradict the hypothesis of a chaotic signal with a single prevalent mode as a time series model of Wolf numbers.

The γ Cas type stars are a group of Be stars with unusually hard X-ray emission and an X-ray luminosity of L_X ~ 10³¹–10³³ erg/s, which is higher than for typical Be stars but less than for massive X-ray binaries with Be components. The temperature of the X-ray emitting plasma reaches values of 10–20 keV or even more, assuming that they emit thermal X-rays. To test the hypotheses on the X-rays formation from this group of stars, the variability of the X-ray and optical emission of γ Cas type stars is analyzed. Regular components of X-ray brightness variations and H, He and FeII line profile variations in spectra of such stars are revealed. The periods of optical and X-ray variability are close and correspond to typical periods of non-radial pulsations (NRPs) of Be stars. That suggests modulation of the wind structure of a Be star as a result of NRPs.

The causes of climate change on Earth represent one of the main questions in modern science. As is known, solar radiation is one of the main factors that determines the physical characteristics of Earth’s atmosphere. Therefore, changes in solar activity cannot but lead to changes in Earth’s climate. It is well known that the Little Ice Age took place on Earth during the Spörer, Maunder, and Dalton deep solar minima. The article analyzes changes in solar activity and Earth’s climate since the beginning of the end of the last global glaciation (approximately 20 000–19 000 years ago). In particular, it is shown that the Mayendorff warming, Dryas coolings, and the Iron Age cooling (in the first millennium BCE) could be associated with changes in solar activity, just like the Little Ice Age.