Geomagnetism and Aeronomy最新文献

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.

The study estimates the contribution of middle-scale solar wind structures (variations recorded by a spacecraft during ~10 min intervals) in turbulence development in the transition region behind the bow shock. The analysis is based on simultaneous measurements of plasma and/or magnetic field parameters in the solar wind, in the dayside magnetosheath, and on the flanks. The study adopts measurements by Wind, THEMIS, and Spektr-R spacecraft. The properties of the magnetic field and ion flux fluctuation spectra are analyzed in the 0.01–4 Hz frequency range, which corresponds to the transition from MHD to kinetic scales. The dynamics of turbulence properties in the magnetosheath is governed by large-scale disturbances, while structures with smaller scales have an effect in the absence of large-scale structures.

The results of identifying trends in the annual average ionospheric indices ΔIG and ΔT are presented, obtained after excluding from IG and T the dependence of these indices on the annual average solar activity indices. The solar activity indices were F10, Ly-α, and MgII—solar radiation fluxes at 10.7 cm, in the Lyman-alpha line of hydrogen (121.567 nm), and the ratio of the central part to the flanks in the magnesium emission band 276–284 nm. Two time intervals (in years) are considered: 1980–2012 and 2013–2023. It was found that in 1980–2012, all analyzed linear trends were negative: the ΔIG and ΔT values decreased over time; they were very weak and insignificant. Fluctuations of ΔIG and ΔT with respect to trends for Ly-α were almost twice as large as for F10 and MgII. In the interval of 2013–2023, all analyzed linear trends intensified and became significant: the rate of decrease in ΔIG and ΔT over time increased. For MgII this rate was almost twice as high as for F10. For 2013–2023, the MgII index overestimated the contribution of solar radiation to ionospheric indices, especially during the growth phase of solar cycle 25, which began at the end of 2019. As a result, in the growth phase of solar cycle 25, the F10 index became a more adequate solar activity indicator for ionospheric indices than MgII. In the interval of 1980–2012, the F10 and MgII indices changed almost synchronously. The growth phase of solar cycle 25 was the first case this synchrony was disrupted for the entire period of MgII measurements.

The article presents the results of a comparative analysis of the solar proton event on March 30, 2022, which has an unusual time profile of solar proton fluxes, and the previous and subsequent solar proton events (March 28, 2022, and April 02, 2022). Increases in energetic proton fluxes in the interplanetary and near-Earth space are associated with successive solar X-ray flares M4.0, X1.3, and M3.9 and three halo-type coronal mass ejections. The study was based on experimental data obtained from spacecraft located in the interplanetary space (ACE, WIND, STEREO A, and DSCOVR), in a circular polar orbit at an altitude of 850 km (Meteor-M2) and in geostationary orbit (GOES-16, Electro-L2). An explanation has been proposed for the specific features of the energetic proton flux profile in the solar proton event on March 30, 2022: protons accelerated in the flare on March 30, 2022 were partially screened by an interplanetary coronal mass ejection, the source of which was the explosive processes on the Sun on March 28, 2022; late detection of maximum proton fluxes, simultaneous for particles of different energies, is due to the arrival of particle fluxes inside an interplanetary coronal mass ejection. The spatial distribution of solar protons in near-Earth orbit was similar to the distribution at the Lagrange point L1 but with a delay of ~50 min.

The induction and momentum equations are simplified to a dynamical system for the kinetic and magnetic energies in Earth’s core. Stable stationary points of this system give a geomagnetic field of ~10 mT and the cosecant of the angle between the magnetic field vector and fluid velocity vector is on average about 500 at a known speed of ~1 mm/s and a generally accepted dynamo power of ~1 TW. With a generally known typical geomagnetic time on the order of 1000 years, harmonic secular variations on the order of several decades and rapid exponential changes on the order of several months, possibly associated with jerks, were obtained. All this agrees well with dynamo theory, paleomagnetic reconstructions, numerical modeling, and observations. A geomagnetic energy of ~10 mJ/kg is four orders of magnitude greater than the kinetic energy. Under conditions of such dominant magnetic energy, an analytical solution was obtained, which over time converges to stable stationary points. Apparently unlikely catastrophes with virtually zero magnetic energy near partially stable stationary points are discussed.

Dayside high-latitude geophysical phenomena provide a ground-based observer with information about the processes at the dayside magnetopause and/or in the adjacent magnetospheric domains. It is assumed that these phenomena are initiated by changes in the parameters of the interplanetary medium and can therefore be used as a tool to investigate the ways in which solar wind energy penetrates through the magnetopause. Such phenomena include magnetic impulses, which are an isolated train of damped oscillations of two to three bursts with a repetition period of 8–12 min. Eight magnetic impulse events were investigated using data from the Scandinavian IMAGE magnetometer network, for which DMSP satellites flew over the observation area during, shortly before, and immediately after the impulse and crossed the boundaries of several domains. From ground-based and DMSP satellite data, it is shown that the downward field-aligned current associated with the impulses is located away from the magnetopause. This means that the impulse cannot be considered as an ionospheric trace of a reconnected flux tube (flux transfer event, FTE) and/or as a traveling convection vortex (TCV). It is found on a larger statistics that the impulse is preceded by marked changes in the By- and Bz-components of the IMF, while the contribution of rapid changes in solar wind pressure and velocity as well as in the Bx-component of the IMF to the generation of the magnetic impulse is not obvious. A possible scenario of the magnetic impulse initiation by IMF variations is discussed.