Search Results (12)

The ionospheric E layer (90–150 km altitude) significantly influences ionospheric dynamics and plays a crucial role in radio wave propagation. The Tibetan Plateau, as the “Third Pole,” affects E-layer morphology due to its unique topographical factors. Given the limited systematic studies in this high-altitude region, this study analyzes E-layer spatiotemporal characteristics and their controlling mechanisms over the Tibetan Plateau and adjacent regions. We analyzed foE (critical frequency of E-layer) data from six ionospheric observation stations across the Tibetan Plateau and neighboring areas during 2013–2023, covering a complete solar cycle from solar minimum to maximum. Combined with sunspot numbers as solar activity indicators, we systematically examined diurnal, seasonal, and solar cycle variations to understand regional E-layer behavior patterns. Daytime foE values significantly exceed nighttime values, demonstrating strong solar control. Spatially, Kunming shows the strongest daytime E-layer intensity with peak values reaching 3.12 MHz, while Urumqi exhibits the weakest at 2.94 MHz. Daytime foE values decrease with increasing latitude, whereas nighttime values show opposite latitudinal trends, indicating pronounced diurnal distribution asymmetry. Kunming displays the largest day-night foE variation amplitude, while Urumqi shows the smallest changes. Notably, most stations exhibit E-layer intensity peaks in July rather than June when solar zenith angles are minimum, differing from typical mid-low latitude seasonal behavior. These patterns may be related to complex vertical atmospheric coupling influenced by the region’s unique topography, which could affect the spatiotemporal distribution of the E-layer over the Tibetan Plateau. Full article

This study investigates the occurrence and distribution of geomagnetic pulsations (Pc2–Pc5) over South America during 2014, analyzing their dependence on magnetic latitude, local time, and geomagnetic activity. Geomagnetic field data were obtained from the Embrace magnetometer network, which spans Brazil and Argentina and includes regions influenced by the Equatorial Electrojet (EEJ) and the South Atlantic Magnetic Anomaly (SAMA). Both continuous and discrete wavelet transforms (CWT and DWT) were employed to analyze non-stationary signals and reconstruct pulsation activity during quiet and disturbed geomagnetic periods. The results reveal that Pc5 and Pc3 pulsations exhibit a pronounced diurnal peak around local noon, with significantly stronger and more widespread activity under storm conditions. Spatial analyses highlight localized enhancements near the dip equator during quiet times and broader latitudinal spread during geomagnetic disturbances. These findings underscore the strong modulation of pulsation activity by geomagnetic conditions and offer new insights into wave behavior at low and mid-latitudes. This work contributes to understanding magnetosphere–ionosphere coupling and has implications for space weather prediction and geomagnetically induced current (GIC) risk assessment in the South American sector. Full article

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. Full article

The sensitivity of Global Navigation Satellite System (GNSS) receivers to ionospheric disturbances and their constant growth are nowadays resulting in an increased concern of GNSS users about the impacts of ionospheric disturbances at mid-latitudes. The geomagnetic storm of June 2015 is an example of a rare phenomenon of a spill-over of equatorial plasma bubbles well north from their habitual. We study the occurrence of small- and medium-scale irregularities in the North Atlantic Eastern Mediterranean mid- and low-latitudinal zone by analysing the amplitude of the scintillation index S4 and rate of total electron content index (ROTI) measurements during this storm. In addition, large-scale perturbations of the ionospheric electron density were studied using ground and space-borne instruments, thus characterising a complex perturbation behaviour over the region mentioned above. The involvement of large-scale structures is emphasised by the usage of innovative approaches such as the ground-based gradient ionosphere index (GIX) and electron density and total electron content gradients derived from Swarm satellite data. The multi-source data allow us to characterise the impact of irregularities of different scales to better understand the ionospheric dynamics and stress the importance of proper monitoring of the ionosphere in the studied region. Full article

Recently, the NOAA has included GNSS (Global Navigation Satellite System) Radio Occultation (RO) data as one of the crucial long-term observables for weather and climate applications. To include more GNSS RO data in its numerical weather prediction systems, the NOAA Commercial Weather Data Pilot program (CWDP) started to explore the commercial RO data available on the market. After two rounds of pilot studies, the CWDP decided to award the first Indefinite Delivery Indefinite Quantity (IDIQ) contract to GeoOptics and Spire Incs. in 2020. This study examines the quality of Spire RO data products for weather and climate applications. Spire RO data collected from commercial CubeSats are carefully compared with data from Formosa Satellite Mission 7–Constellation Observing System for Meteorology, Ionosphere, and Climate-2 (COSMIC-2), the fifth-generation European Centre for Medium-Range Weather Forecasts (ECMWF) atmospheric reanalysis (ERA5), and high-quality radiosonde data. The results demonstrate that, despite their generally lower Signal-Noise-Ratio (SNR), Spire RO data show a pattern of lowest penetration height similar to that of COSMIC-2. The Spire and COSMIC-2 penetration heights are between 0.6 and 0.8 km altitude over tropical oceans. Although using different GNSS RO receivers, the precision of Spire STRATOS receivers is of the same quality as those of the COSMIC-2 TriG (Global Positioning System—GPS, GALILEO, and GLObal NAvigation Satellite System—GLONASS) RO Receiver System (TGRS) receivers. Furthermore, the Spire and COSMIC-2 retrieval accuracies are quite comparable. We validate the Spire temperature and water vapor profiles by comparing them with collocated radiosonde observation (RAOB) data. Generally, over the height region between 8 km and 16.5 km, the Spire temperature profiles match those from RS41 RAOB very well, with temperature biases of <0.02 K. Over the height range from 17.8 to 26.4 km, the temperature differences are ~−0.034 K, with RS41 RAOB being warmer. We also estimate the error covariance matrix for Spire, COSMIC-2, and KOMPSAT-5. The results show that the COSMIC-2 estimated error covariance values are slightly more significant than those from Spire over the oceans at the mid-latitudes (45°N–30°N and 30°S–45°S), which may be owing to COSMIC-2 SNR being relatively lower at those latitudinal zones. Full article

A growing number of SmallSat/CubeSat constellations with high-rate (50–100 Hz) global navigation satellite system radio occultations (GNSS-RO) as well as low-rate (1 Hz) precise orbit determination (GNSS-POD) limb-viewing capabilities provide unprecedented spatial and temporal sampling rates for ionospheric studies. In the F-region electron density (N${}_e$) retrieval process, instead of the conventional onion-peeling (OP) inversion, an optimal estimation (OE) inversion technique was recently developed using total electron content measurements acquired by GNSS-POD link. The new technique is applied to data acquired from the COSMIC-1, COSMIC-2, and Spire constellations. Although both OE and OP techniques use the Abel weighting function in N${}_e$ inversion, OE significantly differs in its performance, especially in the lower F- and E-regions. In this work, we evaluate and compare newly derived data sets using F2 peak properties with other space-based and ground-based observations. We determine the F2 peak N${}_e$ (NmF2) and its altitude (hmF2), and compare them with the OP-retrieved values. Good agreement is observed between the two techniques for both NmF2 and hmF2. In addition, we also utilize autoscaled F2 peak measurements from a number of worldwide Digisonde stations (∼30). The diurnal sensitivity and latitudinal variability of the F2 peak between the two techniques are carefully studied at these locations. Good agreement is observed between OE-retrieved NmF2 and Digisonde-measured NmF2. However, significant differences appear between OE-retrieved hmF2 and Digisonde-measured hmF2. During the daytime, Digisonde-measured hmF2 remains ∼25–45 km below the OE-retrieved hmF2, especially at mid and high latitudes. We also incorporate F-region N${}_e$ measurements from two incoherent scatter radar observations at high latitudes, located in the North American (Millstone Hill) and European (EISCAT at Tromso) sectors. The radar measurements show good agreement with OE-retrieved values. Although there are several possible sources of error in the ionogram-derived N${}_e$ profiles, our further analysis on F1 and F2 layers indicates that the low Digisonde hmF2 is caused by the autoscaled method, which tends to detect a height systematically below the F2 peak when the F1 layer is present. Full article

The ionospheric response at middle latitudes to geomagnetic storms is not yet very well understood. Total electron content (TEC) variations associated with eight strong geomagnetic storms between 2015 and 2022 obtained from GNSS receivers in the eastern area of the North Atlantic (Portuguese continental and insular territory) are studied in an attempt to fill this gap. It was found that for most of the studied geomagnetic storms, TEC variations are synchronous for the longitudinal ranges from 27° W and 9° W. In the southern part of the studied region (around 32° N), the amplitude of TEC variations is, in general, significantly higher than in the northern part (around 39° N). Some of the studied geomagnetic storms were associated with TEC variations that we interpret as effects of post-sunset equatorial plasma bubbles that travelled well north from their habitual region. Additionally, though most of the studied storms were accompanied by reports on different kinds of malfunction of GNSS systems (GPS; GALILEO and other), there is no clear pattern in their appearance in dependence on the geomagnetic/ionospheric storms’ strength, commencement time, and its characteristics, in general. Full article

Centimetre-level accurate ionospheric corrections are required for a high accuracy and rapid convergence of Precise Point Positioning (PPP) GNSS positioning solutions. This research aims to evaluate the accuracy of a local/regional ionospheric delay model using a linear interpolation method across Australia. The accuracy of the ionospheric corrections is assessed as a function of both different latitudinal regions and the number and spatial density of GNSS Continuously Operating Reference Stations (CORSs). Our research shows that, for a local region of 5° latitude ×10° longitude in mid-latitude regions of Australia (~30° to 40°S) with approximately 15 CORS stations, ionospheric corrections with an accuracy of 5 cm can be obtained. In Victoria and New South Wales, where dense CORS networks exist (nominal spacing of ~100 km), the average ionospheric corrections accuracy can reach 2 cm. For sparse networks (nominal spacing of >200 km) at lower latitudes, the average accuracy of the ionospheric corrections is within the range of 8 to 15 cm; significant variations in the ionospheric errors of some specific satellite observations during certain periods were also found. In some regions such as Central Australia, where there are a limited number of CORSs, this model was impossible to use. On average, centimetre-level accurate ionospheric corrections can be achieved if there are sufficiently dense (i.e., nominal spacing of approximately 200 km) GNSS CORS networks in the region of interest. Based on the current availability of GNSS stations across Australia, we propose a set of 15 regions of different ionospheric delay accuracies with extents of 5° latitude ×10° longitude covering continental Australia. Full article

In this study, a global atmospheric model, Specified Dynamics Whole Atmosphere Community Climate Model with thermosphere and ionosphere eXtension (SD-WACCM-X), and the residual circulation principle were used to study the global atmospheric circulation from the lower to upper atmosphere (~500 km) from 2002 to 2019. Our analysis shows that the atmospheric circulation is clearly influenced by solar activity, especially in the upper atmosphere, which is mainly characterized by an enhanced atmospheric circulation in years with high solar activity. The atmospheric circulation in the upper atmosphere also exhibits an ~11 year period, and its variation is highly correlated with the temporal variation in the F10.7 solar index during the same time series, with a maximum correlation coefficient of up to more than 0.9. In the middle and lower atmosphere, the impact of solar activity on the atmospheric circulation is not as obvious as in the upper atmosphere due to some atmospheric activities such as the Quasi-Biennial Oscillation (QBO), El Niño–Southern Oscillation (ENSO), sudden stratospheric warming (SSW), volcanic forcing, and so on. By comparing the atmospheric circulation in different latitudinal regions between years with high and low solar activity, we found the atmospheric circulation in mid- and high-latitude regions is more affected by solar activity than in low-latitude and equatorial regions. In addition, clear seasonal variation in atmospheric circulation was detected in the global atmosphere, excluding the regions near 10⁻⁴ hPa and the lower atmosphere, which is mainly characterized by a flow from the summer hemisphere to the winter hemisphere. In the middle and low atmosphere, the atmospheric circulation shows a quasi-biennial oscillatory variation in the low-latitude and equatorial regions. This work provides a referable study of global atmospheric circulation and demonstrates the impacts of solar activity on global atmospheric circulation. Full article

IONORING (IONOspheric RING) is a tool capable to provide the real-time monitoring and modeling of the ionospheric Total Electron Content (TEC) over Italy, in the latitudinal and longitudinal ranges of 35°N–48°N and 5°E–20°E, respectively. IONORING exploits the Global Navigation Satellite System (GNSS) data acquired by the RING (Rete Integrata Nazionale GNSS) network, managed by the Istituto Nazionale di Geofisica e Vulcanologia (INGV). The system provides TEC real-time maps with a very fine spatial resolution (0.1° latitude x 0.1° longitude), with a refresh time of 10 min and a typical latency below the minute. The TEC estimated at the ionospheric piercing points from about 40 RING stations, equally distributed over the Italian territory, are interpolated using locally (weighted) regression scatter plot smoothing (LOWESS). The validation is performed by comparing the IONORING TEC maps (in real-time) with independent products: (i) the Global Ionospheric Maps (GIM) - final product- provided by the International GNSS Service (IGS), and (ii) the European TEC maps from the Royal Observatory of Belgium. The validation results are satisfactory in terms of Root Mean Square Error (RMSE) between 2 and 3 TECu for both comparisons. The potential of IONORING in depicting the TEC daily and seasonal variations is analyzed over 3 years, from May 2017 to April 2020, as well as its capability to account for the effect of the disturbed geospace on the ionosphere at mid-latitudes. The IONORING response to the X9.3 flare event of September 2017 highlights a sudden TEC increase over Italy of about 20%, with a small, expected dependence on the latitude, i.e., on the distance from the subsolar point. Subsequent large regional TEC various were observed in response to related follow-on geomagnetic storms. This storm is also used as a case event to demonstrate the potential of IONORING in improving the accuracy of the GNSS Single Point Positioning. By processing data in kinematic mode and by using the Klobuchar as the model to provide the ionospheric correction, the resulting Horizontal Positioning Error is 4.3 m, lowering to, 3.84 m when GIM maps are used. If IONORING maps are used as the reference ionosphere, the error is as low as 2.5 m. Real-times application and services in which IONORING is currently integrated are also described in the conclusive remarks. Full article

The changes in the ionosphere during geomagnetic disturbances is one of the prominent Space Weather effects on the near-Earth environment. The character of these changes can differ significantly at different regions on the Earth. We studied ionospheric response to five geomagnetic storms of March 2012, using data of Total Electron Content (TEC) and F2-layer critical frequency (foF2) along the meridian of 70° W in the Northern Hemisphere. There are few ionosondes along this longitudinal sector: in Thule, Sondrestrom, Millstone Hill and Puerto Rico. The lacking foF2 values between the ionosondes were determined by using the experimental latitudinal dependences of the equivalent ionospheric slab thickness and TEC values. During geomagnetic storms, the following features were characteristic: (a) two-hours (or longer in one case) delay of the ionospheric response to disturbances, (b) the more prominent mid-latitude trough and (c) the sharper border of the EIA northern crest. During four storms of 7–17 March, the general tendency was the transition from negative disturbances at high latitudes to intense positive disturbances at low latitudes. During the fifth storm, the negative ionospheric disturbance controlled by O/N₂ change was masked by the overall prolonged electron density increase during 21–31 March. The multiple correlation analysis revealed the latitudinal dependence of dominant Space Weather parameters’ impacts on foF2. Full article

The Global Navigation Satellite System (GNSS) differential code biases (DCBs) are a major obstacle in estimating the ionospheric total electron content (TEC). The DCBs of the GNSS receiver (rDCBs) are affected by various factors such as data quality, estimation method, receiver type, hardware temperature, and antenna characteristics. This study investigates the relationship between TEC and rDCB, and TEC and rDCB stability during a three-year period from 2014 to 2016. Linear correlations between pairs of variables, measured with Pearson’s coefficient ( $R$ ), are considered. It is shown that the correlation between TEC and rDCB is the smallest in low-latitude regions. The mid-latitude regions exhibit the maximum value of $R$ . In contrast, the correlation between TEC and rDCB root mean square (RMS, stability) was greater in low-latitude regions. A strong positive correlation ( $R\ge 0.90$ ) on average between TEC and rDCB RMS was also revealed at two additional GNSS stations in low-latitude regions, where the correlation shows clear latitudinal dependency. We found that the correlation between TEC and rDCB stability is still very strong even after replacing a GNSS receiver. Full article