Geomagnetism and Aeronomy最新文献

This study investigates the ionospheric response over the East Africa region during solar flares and a geomagnetic storm from 8–15 May 2024. During this period, 12 X-class solar flares and one extreme geomagnetic storm occurred, causing pronounced variability in total electron content (TEC). X-ray flux measurements from the Extreme Ultraviolet and X-ray Irradiance Sensors (EXIS) on board the Geostationary Operational Environmental Satellites (GOES) are analyzed to detect solar flares. TEC derived from four GNSS receiver stations and the IRI-2020 model, O/N₂ ratio maps, and an ionospheric electric fields model are used to identify ionospheric variation owing to the space weather events. The X-class flares prior to May 11 produced immediate TEC enhancements of up to +15 TECU relative to quiet day levels, consistent with sudden ionospheric disturbances. In contrast, the geomagnetic storm on May 10–11 induced both positive and negative storm phases, with TEC deviations ranging from –31.46 to +33.13 TECU. During the main phase of the geomagnetic storm, at the ADIS station, TEC increased by +10.8 TECU and then decreased by –8 TECU. In the recovery phase, it increased to +31 TECU. At the DJIG station during the main phase, TEC decreased by –16.1 TECU, followed by a significant positive enhancement reaching +30.5 TECU on May 12th. Similarly, the MAL2 station recorded a minimum negative TEC deviation of –16.6 TECU during the main phase, with a notable maximum positive deviation of +33.03 TECU also occurring on May 12th. For the MBAR station, the main storm phase on May 10th showed a minimum negative TEC deviation of –15.94 TECU, and a maximum positive deviation of +33.13 TECU was observed on May 12th. We have used correlation coefficients ((r)), Percentage Root-Mean Square Error (PRMSE) and root mean square errors (RMSE) to examine the variation of the IRI-2020 TEC from the GPS TEC during the storm. The results show that the model performed best at the ADIS station, with the highest (r) (0.93) and the lowest RMSE (13.33) and PRMSE (28.31%). These study enhance our understanding of solar flare and geomagnetic storm impacts in equatorial and low latitude regions, which is crucial for improving space weather forecasting and mitigating risks.

In this paper, we employ equatorial-latitude Global Navigation Satellite System (GNSS) data from TERONET to investigate the storm that occurred on August 27, 2021. To characterize the equatorial and mid-latitude ionosphere during the storm, the 10 quietest days of August 2021 were selected as background TECs, and we calculated the relative TEC (rTEC) from the deviation of the disturbed days using a median value of the TEC at each timestep, considering all 10 days and selecting the threshold |–30 ≤ rTEC ≥ 30| for the TEC anomaly. Additionally, we employ the African geodetic reference frame (AFREF) GNSS network to analyze the data from 19 stations in the African region during storms. We employ ROTI_ave as a proxy for scintillation to study irregularities and GNSS fluctuations during storm main and recovery phases and examine thermospheric variations from the [O]/[N₂] ratio. Again, we employ the depression of the horizontal component (H) of the Earth’s magnetic field obtained from equatorial and mid-latitude magnetometers to feature the seeding of the TEC enhancements and depression. Our major findings reveal that ionospheric irregularities at low latitudes, as observed from GNSS measurements, show distinct latitudinal differences and seem not well experienced at the dip equator. The equatorial and mid-latitude ionosphere of the Africa sector shows a complex irregularity occurrence that may not have a stronger effect of the solar activity cycle but seems to follow storm-enhanced density, where morning-hour positive storms govern irregularities during the commencement of storms preceded by the equatorial ionization anomaly (EIA) due to localized expansion of the neutral atmosphere.

Ionospheric variability due to solar flares has been studied at different latitudes during the solar cycle 24. In the course of this cycle 24 on September 6, 2017, two powerful and intense solar flares of class X2.2 and X9.3 were emitted by the Sun at 0857 UT and 1153 UT respectively. To examine the ionospheric response simultaneously at low, mid, and high latitudes, total electron content (TEC) values derived from Global Navigation Satellite System (GNSS) receivers were investigated during the solar flare of September 6, 2017, which are the most remarkable flare events during the solar cycle-24. Our observations show a noticeable enlargement in TEC at low, mid, and high-latitude stations. Further, the mean method has been used to investigate TEC variations due to solar flares at low, mid, and high latitudes and considered all PRN which has a one-to-one correlation with the time of solar flares. We describe our findings in the context of earlier research which examined the correlation between change in VTEC (DVTEC) and solar fluxes in X-class solar flares. The aim of this study is to minimize the latitudinal variability of total electron content (TEC) during such events, although the extent of TEC increase seems to be influenced by the class of the solar flare. The results exhibited that X-class flare effects were more pronounced at low latitudes in comparison to mid and high latitudes.

Geomagnetic storms, driven by solar wind–magnetosphere interactions, can significantly disturb the ionosphere, altering electron density and degrading satellite-based communication and navigation systems. The extended geomagnetic storm that occurred from November 5–6, 2023, presents a noteworthy but little-studied chance to investigate its multi-parameter impacts on the ionosphere of South Africa. Although previous research has examined ionospheric disturbances in the area, this event’s prolonged duration and dynamic solar wind solar wind parameters. The findings show significant TEC depletion at five GPS stations. The most noticeable decrease was seen at Springbok (SBOK) on November 6, when the minimum (Delta )TEC was –35.88 TECU in comparison to International Quiet Days for the case of severe geomagnetic storms and latitudinal positions. Magnetic field data from the Hartebeesthoek observatory showed significant storm-time disturbances in the northward (X), eastward (Y), and horizontal (H) components. These variations are attributed to intensified ionospheric Hall and Pedersen currents, where X reflects the dominant Pedersen current aligned with the geomagnetic field, Y indicates enhanced Hall currents due to zonal electric fields, and H captures the net horizontal current response. Furthermore, Global Ultraviolet Imager (GUVI) satellite measurements recorded a sharp decline in the thermospheric O/N₂ ratio over South Africa during the main phase of the storm, indicative of increased recombination rates that suppress electron density. These findings underscore the importance of continued space weather monitoring and ionospheric modeling in the African region to support GNSS reliability and regional forecasting capabilities.

This study presents a comparative statistical analysis of solar activity during the first six years of Solar Cycles 24 (2008–2013) and 25 (2019–2024). The analysis focuses on key solar and geophysical parameters, including sunspot numbers, halo coronal mass ejections (CMEs), solar radio flux at 10.7 cm (F10.7), and geomagnetic storms, to assess differences in solar behavior between the two cycles. Sunspot numbers varied between 0 and 139.1 in Solar Cycle 24, whereas they ranged from 0.2 to 216 during the corresponding period of Solar Cycle 25. Similarly, the F10.7 cm radio flux fluctuated between 65.7 and 153.5 in solar flux unit (s.f.u.) during 2008–2013, and between 67.05 and 245.6 s.f.u. from 2019 to 2024, reflecting an overall increase in solar output. The study also includes an analysis of halo CMEs, with 192 events observed during Solar Cycle 24 and 227 during Solar Cycle 25, both characterized by an angular width of 360°. Geomagnetic activity was assessed using 104 events from Cycle 24 and 179 from Cycle 25, with disturbance storm time (Dst) index values ranging from –50 to –350 nT. The results indicate a significant increase in solar activity during the early phase of Solar Cycle 25 compared to Solar Cycle 24. This suggests a more intense and dynamic space weather environment in the current solar cycle, which may have important implications for space weather forecasting and satellite operations.

This study aims to investigate the energy transfer mechanisms and the behavior of thermal conductivity of this region by examining the thermal conductivity coefficients calculated for critical altitudes in the F region of the ionosphere. Electron-ion collisions and the geometry of the magnetic field affect these coefficients. The thermal conductivity in the ionosphere can exhibit anisotropic properties (different values in different directions) due to the directional dependence of the Earth’s magnetic field. Theoretical approaches have been used and numerical calculations have been performed to analyze the thermal conductivity of the ionosphere. The findings indicate that the magnitudes of the thermal conductivity coefficients were at the level of electrical conductivity and the tensor elements (K_zx, K_xz, K_yz, K_zy) were negative, while the K_yx, K_xy elements were positive up to the equator and then became negative. This phenomenon, called effective thermal conductivity, is not actually a negative value for thermal conductivity, but rather an unusual situation resulting from the direction-dependent effect of the magnetic field. It has been determined that the magnitudes of the tensor elements on March 21 are slightly greater than those on September 23.

The present study investigates the subauroral ionospheric response to geomagnetically disturbed conditions across different seasons of 2012, using Total electron content (TEC) and S4 index data derived from a Global Positioning System (GPS) receiver installed at the Indian Antarctic station Maitri (geographic coordinates: 70.76° S, 11.74° E). TEC and S4-index measurements for January, March, and June 2012 were analysed alongside the corresponding Auroral Electrojet (AE) index and the interplanetary magnetic field (IMF) Bz component to assess seasonal variability in ionospheric behaviour. The results reveal that the subauroral ionosphere exhibits a negative response (i.e., TEC depletion) during periods of southward IMF Bz orientation, whereas a positive response is generally observed during northward IMF Bz, particularly during the summer and equinoctial periods. In contrast, this trend appears to reverse during the winter season. The observed negative ionospheric responses are attributed to a combination of equatorward plasma transport and thermospheric compositional changes. Additionally, poleward compression of the auroral oval and enhanced molecular precipitation are believed to contribute to these depletions. Furthermore, the study examines the occurrence characteristics of amplitude scintillations under disturbed geomagnetic conditions. It is observed that the intensity of amplitude scintillation during the winter (polar night) is significantly higher compared to that during summer and equinox periods, suggesting enhanced small-scale ionospheric irregularities under such conditions.

We analyzed the occurrence and characteristics of various types of magnetic storms during solar cycle 24. The annual mean total sunspot number (SSN) was used to quantify solar cycle activity. The intensity and classification of magnetic storms, by type and rank, were assessed using two geomagnetic indices: Dst (Disturbance Storm Time Index) and aa (global geomagnetic activity index), respectively. Based on the minimum Dst values, we identified a total of 130 magnetic storm events, comprising 104 moderate and 26 intense storms. Using the maximum aa values, we further classified these events by type and rank. Among them, 54 storms displayed sudden commencement (S-storms), while 76 storms exhibited gradual commencement (G-storms). Additionally, the types of storms were categorized by five ranks. According to established literature, the main common sources of storms are issued from interplanetary coronal mass ejections (ICMEs) and corotating interaction regions (CIRs). Our findings revealed that 76% of storms associated with ICME sources were S-storms, typically occurring near the peak of solar activity. Conversely, 60% of storms related to CIR sources were G-storms, most commonly observed during the declining phase of the solar cycle. This study contributes to the broader understanding of magnetic storm behavior during solar cycle 24, in terms of both intensity and classification. Lastly, we compared the distribution of storms in solar cycle 24 with those of previous cycles to contextualize the overall activity level.

Estimating with low uncertainty the parameters of time and magnitude of upcoming earthquakes is necessary to create an earthquake warning system. Nowadays, by using different satellite data, it is possible to monitor a large number of earthquake precursors. Multi-precursor analysis, along with multi-method analysis, has made it possible to detect a large number of LAI (lithospheric atmospheric ionospheric) seismic anomalies in the study of strong earthquake-affected areas. In this study, the deviation values of 898 LAI anomalies detected using 20 implemented predictor algorithms around the time and location of 21 powerful earthquakes that occurred in recent years have been considered. Using different scenarios, various functions were fitted on the collected data, including the day of anomaly observation, anomaly intensity, geographic latitude of epicenter and real magnitude of the earthquake, and functions were developed to estimate magnitude parameters with RMSE of about 0.53 (M_W) and the day of the earthquake with about RMSE of 8.27 day. In addition, by using an MLP neural network, and training it using the detected LAI anomalies, accuracies of 0.21 and 9.29 were obtained, respectively, for estimating the magnitude and time of an impending earthquake. Therefore, by comparing the two functional and machine learning-based methods proposed in this study, it can be concluded that the proposed functions are efficient for estimating magnitude and time of forthcoming strong earthquakes. Although the accuracy of predicting the magnitude of the earthquake is acceptable, the accuracy of about 8 days for predicting the day of the earthquake can be efficient for relatively short-time earthquake prediction.

Geomagnetic storms (GSs), driven by solar activity, produce significant disturbances in the Earth’s magnetic field—particularly in its horizontal component (H). This study investigates the response of the H-component to GSs during solar cycle 24 (2009–2019), using ground-based magnetometer data recorded at the TAM observatory in Tamanrasset, Algeria (22.79° N, 5.53° E), part of the INTERMAGNET network. A total of 130 storms were identified based on Dst-index thresholds and classified into 104 moderate (–100 nT < Dst ≤ –50 nT) and 26 intense (Dst ≤ –100 nT) events. The H-component was derived from the orthogonal north and east components (X, Y) of the geomagnetic field. The results reveal a gradual upward trend in the H-component over the solar cycle, consistent with secular geomagnetic field variations. However, during storm periods, the H-component exhibited significant decreases. These disturbances were quantified using the maximum deviation parameter ΔH_max, which displayed a statistically significant positive correlation with storm intensity (r = 0.71). Notably, the correlation was stronger for intense storms (r = 0.75) than moderate ones (r = 0.38). These results highlight the greater sensitivity of low-latitude geomagnetic observatories to high-intensity storms and demonstrate the diagnostic value of ΔH_max for space weather monitoring.