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The present work examines the spatial and temporal distribution of positive and negative TEC anomalies on the global and regional scale. To study the local response of the ionosphere, foF2 data from ground ionosonde stations and TEC data from Madrigal and CODE databases have been used. The relative deviation, which also determines the type of TEC response during geomagnetic storms on 3 and 4 February 2022, is considered. In the present study, the regions of positive and negative TEC anomalies and their evolution during storms are examined in detail. As a result of the study, estimates of the following were obtained: (i) the location of the sectors of the polar regions, in where the particle precipitation from the solar wind is observed, (ii) the mid-latitude regions, in which the mechanism of influence of the O/N2 ratio dominates, and (iii) the region around the equator, in which the influence of the electric field dominates. An attempt was made to determine which mechanism of influence of geomagnetic storms on the ionospheric electron density is dominant in different regions. The following main mechanisms are considered: (a) the additional ionization from the particles’ precipitation, (b) the change of the ratio of atomic oxygen (O) to molecular nitrogen (N2) due to the heating of the neutral air, and (c) the influence on the equatorial ionospheric anomaly.

The main idea of the present study is to investigate in detail the time evolution of the spatial inhomogeneities connected with the ionospheric response to the geomagnetic storm registered in the period of 10–11 May 2024. The obtained ionospheric anomalies represented by the relative deviations of the global Total Electron Content (TEC) data have been utilized in the analysis. The used global TEC data have been converted to a coordinate system with a modip latitude and geographical longitude. In addition to the maps illustrating the global spatial distribution of the geomagnetically forced ionospheric anomalies, a presentation of the observed longitudinal structures by sinusoidal approximation has also been used. The resulting positive and negative responses have been studied depending on the magnetic latitude, local times and the behavior of the geomagnetic activity parameters during the considered event. The interpretation takes into account the known mechanisms for the effect of the geomagnetic storm on the electron density. A special attention is focused on the differences in the two hemispheres at high and mid latitudes, where a simultaneous direct impact of the particle precipitation and the change in the temperature regime of the neutral atmosphere has been assumed. The low-latitude response as a result of the Equatorial Ionization Anomaly (EIA) associated with Disturbed Dynamo Electric Fields (DDEFs) and its relationship with local time has also been considered.

The basic concept of this study is to investigate, by correlation analysis, the relationship between geomagnetic activity and Total Electron Content (TEC) for the period from 1994 to 2023. The global TEC data used have been recalculated to a coordinate system with a modip latitude and geographical longitude. In the analysis of the parameters used, the global index of geomagnetic activity, Kp, and TEC were converted into relative values, showing the deviation from stationary (quiet) conditions. The investigation defined theoretical cross-correlation functions that allow estimating the time lag constant from the shift of the maximum cross-correlation. The seasonal dependence of the ionospheric response was investigated by splitting it into three monthly segments centered on the equinox and solstice months. The dependence of the ionospheric response on local time was studied by creating time series, including those longitudes at which, at a given moment, the local time coincides with the selected one. The results show the following peculiarities in the TEC response: the type of ionospheric response (positive or negative) in each of the latitudinal zones (auroral ovals, mid-latitude and low-latitude) depends on the season, the local time of the geomagnetic storm and the specific physical mechanism of impact.

This research examines in detail the behavior of the Equatorial Ionization Anomaly (EIA) during a severe geomagnetic storm that occurred on 10–11 October 2024. The global data of Total Electron Content (TEC) represented by relative deviation, giving information about the variations compared to quiet conditions, were used. The main attention is paid to the appearance of an additional “fountain effect” under the action of disturbed dynamo currents and the vertical drift of the ionospheric plasma caused by them. The results show that the area in which a positive response (increase) of TEC is observed occurs in an area corresponding to local time around 18–20 h (longitude around 60 °W) at magnetic latitudes ±30° and during the storm shifts westward to around 180 °W. The westward drift of the storm-induced “fountain effect” is moving at a speed much slower than the Earth’s rotation speed. As a result, the area of positive TEC response (vertical upward drift) and the area of negative response (vertical downward drift) are localized in both nighttime and daytime conditions. In this investigation, an example of a very similar geomagnetic storm registered on 25 September 1998 is given for comparison, in which a similar stationing of the storm-induced EIA was observed at longitudes around 180 °E.

In the present paper, the response of the ionospheric Total Electron Content (TEC) at low latitudes during several geomagnetic storms occurring in different seasons of the year is investigated. In the analysis of the ionospheric response, the following three geomagnetic events were selected: (i) 23–24 April 2023; (ii) 22–24 June 2015 and (iii) 16 December 2006. Global TEC data were used, with geographic coordinates recalculated with Rawer’s modified dip (modip) latitude, which improved the accuracy of the representation of the ionospheric response at low and mid-latitudes. By decomposition of the zonal distribution of the relative deviation of the TEC values from the hourly medians, the spatial distribution of the anomalies, the dependence of the response on the local time and their evolution during the selected events were analyzed. As a result of the study, it was found that the positive response (i.e., an increase in electron density relative to quiet conditions) in low latitudes occurs at the modip latitudes 30° N and 30° S. An innovative result related to the observed responses during the considered events is that they turn out to be relatively stationary. The longitude variation in the observed maxima changes insignificantly during the storms. Depending on the season, there is an asymmetry between the two hemispheres, which can be explained by the differences in the meridional neutral circulation in different seasons.

In the present work, the variations in Total Electron Content (TEC) induced by changes in the ionizing radiation of the Sun, which are related to the rotation period (about 27 days), were investigated. This study was based on a 30-year period. The relative deviations in the TEC and F10.7 values were used in the data analysis. The use of this modification aimed to eliminate the stationary diurnal, seasonal, and solar course of the TEC over the course of the long-term variations in solar activity, preserving the variations within a time scale of 27 days and less. As a result, the values of the linear regression coefficient between the relative deviations in the two considered quantities from the median (quiet conditions) for one rotation period were obtained. Depending on the general level of solar activity, the season, and the latitude, this coefficient varied between 40% and 60%. The analysis showed that the minimum values were observed during high solar activity. The latitudinal distribution demonstrated an increase in the area of the Equatorial Ionization Anomaly (EIA) under the influence of the so-called “fountain effect”. As a result, there was a seasonal variation and an increase in the winter months at mid and high latitudes and a decrease in the months of the minimum zenith angle of the Sun at low latitudes. A well-pronounced asymmetry in the equinox months was also obtained. The obtained results are the novelty of this study and can be used to improve empirical models for short-term TEC forecasting.

A study of the behavior of the main characteristics of the ionosphere over Europe during the 26–28 February 2023 ionospheric storm was carried out in this present work. The additional influence of sudden stratospheric warming on the ionosphere was considered. The behavior of the critical frequency of the ionosphere foF2 (characterizing the maximum electron density), the peak height of the F2-layer (hmF2), and Total Electron Content (TEC) were investigated through their relative deviations from the quiet conditions. The behavior of the TEC over Europe showed the geographic latitudinal dependence of the response. The variability in the ionospheric critical frequency was represented by the data of 10 ionospheric stations for vertical sounding located in two groups: (i) near the prime meridian and (ii) near the 25° E meridian. Some differences were found in the response compared to the TEC response, which was explained by the different responses of the top maximum region and bottom maximum region. The peak height of the F2 layer varied strongly during the storm, which was due to the forced drift of ionospheric plasma induced by additional electric fields. The present detailed analysis of the ionospheric response shows that the considered storm exhibited characteristic features inherent in the winter season but with some manifestations of reactions in equinox conditions.

This paper presents for the first time the global latitude structure and seasonal variability of the ionospheric response to the forced from below DE3 and DE2 tides during the period of time January 2008–March 2009. The COSMIC hmF2 and SABER temperature data have been utilized in order to define the ionospheric DE3 and DE2 tidal response to the DE3 and DE2 temperature tides propagating from below. The COSMIC DE3 and DE2 hmF2 tidal oscillations are derived by the same method as the tides seen the SABER temperatures. It has been shown that the longitude wave‐4 and wave‐3 hmF2 structures observed respectively in September and May 2008 are forced mainly by DE3 (wave‐4) and DE2 (wave‐3) temperature tides coming from below. The longitude wave‐3 hmF2 structure observed in January 2008 however is forced by the combined action of the DE2 temperature tide coming from below and the SPW3 probably generated in‐situ.

This paper presents climatological features of the longitudinal structures WN4, WN3, and WN2 and their drivers observed in the lower thermospheric temperatures and in the ionospheric TEC. For this purpose, two long-term data sets are utilized: the satellite SABER/TIMED temperature measurements, and the global TEC maps generated with the NASA JPL for the interval of 2002–2022. As the main drivers of the longitudinal structures are mainly nonmigrating tides, this study first investigates the climatology of those nonmigrating tides, which are the main contributors of the considered longitudinal structures; these are nonmigrating diurnal DE3, DE2, and DW2, and semidiurnal SW4 and SE2 tides. The climatology of WN4, WN3, and WN2 structures in the lower thermosphere reveals that WN4 is the strongest one with a magnitude of ~20 K observed at 10° S in August, followed by WN2 with ~13.9 K at 10° S in February, and the weakest is WN3 with ~12.4 K observed over the equator in July. In the ionosphere, WN3 is the strongest structure with a magnitude of 5.9 TECU located at −30° modip latitude in October, followed by WN2 with 5.4 TECU at 30 modip in March, and the last is WN4 with 3.7 TECU at −30 modip in August. Both the climatology of the WSA and the features of its drivers are investigated as well.

In this investigation, a comparison is presented between variations in temperature and ozone concentration at different altitude levels in the stratosphere for the Northern Hemisphere in the conditions of Sudden Stratospheric Warming (SSW) for the period January–March 2023. Spatial and altitude distribution of atmospheric characteristics derived from MERRA-2 are represented by their Fourier decomposition. A cross-correlation analysis between temperature and Total Ozone Column (TOC) is used. The longitudinal inhomogeneities in temperature, caused by stationary Planetary Waves with wavenumber 1 (SPW1), are found to be significant at altitudes around the maximum of the maximum of the ozone number density vertical distribution. As a result, it is established that the latitudinal and longitudinal distribution of TOC has a noticeable similarity with that of the temperature at altitudes close to the ozone concentration maximum. The results of correlation between temperature at individual stratospheric levels and ozone concentration show that (i) in the region around the ozone concentration maximum, the correlation is high and positive, (ii) at higher altitudes the sign of the correlation changes to negative (~37 km). The examination shows that the anomalous increases in TOC during SSW are due to an increase in ozone concentration in the altitudes between 10 km and 15 km.