Geomagnetism and Aeronomy最新文献

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.

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.

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.

Here we studied the planetary features of the spatiotemporal distribution of ionospheric electrojets recorded in the onset of a substorm and in time on the activity maximum of three very intense substorms (with an AL-index from –1200 to –1700 nT) observed during the main phase of the strong magnetic storm on March 23−24, 2023. We have analyzed the substorms by applying the global maps of the planetary distribution of high-latitude ionospheric currents, compiled from simultaneous magnetic measurements on 66 low-orbit satellites of the AMPERE project, as well as ground-based magnetograms from the Scandinavian IMAGE profile and mid-latitude IZMIRAN stations located in the same longitudinal region. It was established that the onset of all the studied substorms on the IMAGE meridian was accompanied by the development of a nighttime current vortex with clockwise rotation, which is an indicator of an increase in downward field-aligned currents. The ground-based mid-latitude observations at the IZMIRAN station network confirmed that the center of the current wedge of the substorm was located in the nighttime sector significantly east of the IMAGE meridian. In the time of the substorm intensity maximum, a similar but more extensive current vortex was observed in the morning sector, which is probably typical of intense substorms.

In this work the problem of reconstructing the vector anomalous magnetic field from single-component data was solved by means of artificial neural networks. For training an artificial neural network a database of anomalous magnetic field components ({{B}_{x}}), ({{B}_{y}}), ({{B}_{z}}) was created using a set of point magnetic dipoles lying under the field measurement plane. Using a synthetic example, the work of a trained neural network was shown in comparison with a well-known numerical algorithm for restoring a vector field from data of one component. Further, according to the data of the vertical component of the anomalous geomagnetic field the horizontal components of the anomalous geomagnetic field were restored using artificial neural networks in the territory of 58°–85° E, 52°–74° N with a grid step of 2 arc minutes.

The impact of the Weddell Sea Anomaly on the structure of the nightside ionosphere in the summer Southern Hemisphere is considered in detail. For this, data from the CHAMP satellite were used in January 2003 under high solar activity and in January 2008 under low solar activity. The data relate to the local time interval 02−04 LT, when the increase in electron density due to the formation of the anomaly is the strongest. At longitudes of 60°−180° E under high solar activity and 0°–210° E under low solar activity, where there is no anomaly, the main ionospheric trough is observed. The plasma peak in the nightside ionosphere associated with formation of the anomaly reaches 6 MHz under low solar activity and 10 MHz under high solar activity. The strongly developed plasma peak decreases sharply to high latitudes at the equatorward boundary of auroral diffuse precipitation, which corresponds to the plasmapause. When the anomaly is weakly developed, the contribution of diffuse precipitation becomes noticeable, so that the plasma peak expands poleward due to this precipitation. Poleward of the anomaly, the high-latitude trough is usually observed at latitudes of the auroral oval. A well-defined electron density minimum is often formed equatorward of the Weddell Sea Anomaly, which can be defined as a subtrough. Sometimes the subtrough is created by the escape of ionospheric plasma from the summer to the winter hemisphere. Then a density maximum forms in the winter hemisphere at adjacent latitudes. A subtrough is much more common under low solar activity than under high.

Positioning, navigation and time are the cornerstones of satellite navigation. These aspects are frequently affected by ionospheric variations caused by solar flares (SF). In this study, we have attempted to predict the range error (RE) caused by ionospheric delay in Global Positioning System (GPS) signals during six different X-class SF that occurred in the 25th solar cycle using two different approaches, namely, a recurrent neural network (RNN) and the ordinary Kriging-based surrogate model (OKSM). The total electron content (TEC) collected from Hyderabad station along with other input parameter includes the Planetary A and K index (Ap and Kp), solar sunspot number (SSN), disturbance storm time index (Dst), and radio flux measured at 10.7 cm (F10.7) were used for prediction. The OKSM uses the previous six days of datasets to predict the RE on the seventh day, whereas the RNN model uses the previous 45 days of datasets to predict the RE on the 46th day. The performance of both models is evaluated using statistical parameters such as root mean square error (RMSE), normalized root mean square error (NRMSE), Pearson’s correlation coefficient (CC), and symmetric mean absolute percentage error (sMAPE). The results indicate that the OKSM performs well in adverse space weather conditions when compared to RNN.

Ionospheric sporadic E layers are very thin, but with a much higher electron density than normal E regions that occur at altitudes of about 90–130 km. Vertical wind shear is considered the main source of mid-latitude sporadic E layer formation, which leads to periodicity, such as 24-h, 12-h, and so on. In this paper, a time series analysis of the critical frequency of the sporadic E layer (foEs) observed by an ionosonde is performed at seven stations (spanning about 37° N–51° N and 29° S–67° S) to investigate the terdiurnal signature in it. Except for the already known 24-h and 12-h periodicities features which are related to diurnal and semidiurnal tides, new findings are also obtained. The 8-h periodicity is a regular and repeatable feature at high mid-latitude regions of both hemispheres. The 8-h periodicity is more prominent at mid-latitudes (~50° N and ~60° S) during the winter and spring months of the hemisphere, which agrees with the terdiurnal tide features. It also shows that the amplitude of the 8-h periodicity is equivalent to the 12-h periodicity component in summer and autumn and almost the same as the 24-h periodicity component in winter under certain circumstances. This indicates that the 8-h periodicity should be taken into consideration for sporadic E layer modeling.

Geomagnetic storms are disorders in Earth’s magnetic field triggered by solar activity. This research attempts to foretell the total electron content (TEC) using the Kriging and AI model in both low and mid-latitude stations during strong geomagnetic storms that happened on March 17, 2015 and February 3, 2022. This research paper focuses on predicting and analysing TEC anomalies in the ionosphere during the solar storm by using three models: ordinary kriging (OK), cokriging (CoK) and recurrent neural network (RNN). The predicted TEC values by the models are justified with the TIEGCM and KMPCA models. Parameters like RMSE, CC, MAE, and MAPE were applied to assess the execution of predictive models and to quantify the accuracy of predictions. The average RMSE for TEC predicted in the low-latitude region ranges from 4.90 to 5.41, 5.85 to 6.26 and 8.50 to 9.90 for the OK, CoK, and RNN models, respectively. Likewise, the average RMSE for TEC predicted in the mid-latitude region ranges from 1.81 to 4.04, 1.91 to 4.24 and 2.77 to 5.38 for the OK, CoK, and RNN models, respectively. The performance evaluation parameters show that the OK performs better than the CoK and RNN models.

Events of induced proton precipitations from the inner radiation belt have been detected. They accompanied almost a half (11) of 25 anomalous electron precipitations recorded onboard the Meteor-M No. 2 satellite in 2014−2022 in Oceania at low latitudes in the morning hours of local time under quiet geomagnetic conditions. It is surmised that such events could be provoked by proton fall into cyclotron resonance with low-frequency radiation stimulated by a mobile ionospheric heater. The observed effects in anomalous electron precipitations which may be interpreted in the framework of the mobile ionospheric heater conception are also discussed.