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Abstract Single frequency users of the Global Navigation Satellite System (GNSS) should correct the ionospheric delay to obtain positioning solutions. A valuable source of ionospheric delay corrections is the global ionospheric models (GIMs) of Vertical Total Electron Content. The accuracy of GIMs is therefore important to improve the positioning accuracy. One of the main issues that affects the GIM performance, especially at low latitude regions, is the high sensitivity of the global positioning system (GPS) L2 frequency to ionospheric scintillation. As an attempt to overcome this issue, in this work, we study the capabilities of using only GPS L1 frequency to compute ionospheric corrections in form of regional ionospheric maps. The performance of the new ionospheric model is evaluated by means of single frequency precise point positioning, comparing the positioning results against the correction using dual‐frequency GPS signals, as well as compared to the corrections provided by GIMs produced by the international GNSS service. As a result, the positioning performance using single frequency model presented similar accuracy to the dual frequency models and, at the same time, provided less observations affected by ionospheric scintillations. These results demonstrate the feasibility of using single frequency GNSS data to develop ionospheric models and to improve the positioning over low latitudes.

Abstract Vertical total electron content (VTEC) has great importance in describing the ionosphere. VTEC values are commonly distributed in regular grids by means of so‐called global ionospheric maps (GIMs) and regional ionospheric maps (RIMs). Although considerable research has been conducted to develop regional and global models, there is no clear understanding of the benefits of using RIMs over GIMs. Aiming to contribute to this discussion, our investigation presents a comparison between seven global and regional ionospheric maps considering two approaches: (a) ionosonde data‐based assessment and (b) global navigation satellite systems (GNSS) positioning assessment. A challenging low latitude ionosphere scenario, the Brazilian region, was selected during a week with an active geomagnetic storm. The assessment results with ionosonde data have shown better performance of the RIM products named OTHR and OTRG. Among the global products, CODG and UQRG have shown the best performances. The worst results were obtained with the RIM named Instituto Nacional de Pesquisas Espaciais. The assessment with GNSS positioning led to larger and noisier errors close to the equatorial anomaly. Two of the analyzed RIMs presented expected large errors in stations at the edges of the coverage area. To overcome this issue, a hybrid product was proposed to extend the RIM covered region. The proposed hybrid product (OTRG) presented the best results in the GNSS positioning domain.

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.

Abstract The determination of the ionospheric perturbation degree is essential to describe the ionosphere state for space weather monitoring. A new method for estimating the spatial and temporal components of the Vertical Total Electron Content (VTEC) gradient is introduced. The new method is based on VTEC estimated at each grid point of Global Ionosphere Map (GIM) by the UPC‐IonSAT research group of the Universitat Politècnica de Catalunya. Depending on the requirement, the VTEC spatial gradients can be derived at selected regions or grid points of the GIM on a global scale. According to the comparison with previous studies over the Europe region during quiet ionosphere state and two severe geomagnetic storms, the new method has proven to be reliable and has a great potential for the monitoring of ionospheric perturbation degree on a global scale. In addition, the associated warning of disturbed ionosphere might be available in the context of the on‐going development of real‐time GIMs.

Abstract The ionospheric storms have adverse effects on the radio communications, satellite communications and also the Global Navigation Satellite Systems (GNSS) application. A new Ionospheric storm Scale from Universitat Politècnica de Catalunya (UPC) Global Ionosphere Map (GIM), IsUG, is introduced for characterizing the ionospheric state on a global scale. The IsUG is based on the Vertical Total Electron Content (VTEC) derived from the continuously computed UPC Quarter‐of‐an‐hour time resolution Rapid GIM (UQRG), taking as reference the ones during the period 1997 to 2014. It is similar to the I‐scale index previously introduced, although it was over Japan and based on raw GNSS data. The dependence of the VTEC on season, local time and geographical location at each grid point of UQRG is removed by normalizing (i.e., by substracting the mean and dividing by the corresponding standard deviation) the percentage deviation of hourly median VTEC. After validating IsUG versus I‐scale, the IsUG distribution is presented and analyzed at global scale during a severe geomagnetic storm from 7 to 10 November 2004 as an example of the potentialities of the new index. The results suggest that the IsUG global map has a great potential for the scientific study of ionospheric storms from a global perspective and also for space weather warning considering the accuracy of the recently developed real‐time GIMs.

Abstract An alternative approach to detect solar flares and quantify the associated extreme ultraviolet (EUV) solar flux rate was introduced in this journal by the authors: Global Navigation Satellite Systems Solar FLAre Indicator (GSFLAI) was founded on the dependence of the sudden electron content increase of the Earth ionosphere versus the angle regarding the flare source, the Sun, given by a simple but accurate first‐principles‐based model. Such overionization is directly measured from the dual‐frequency phase measurements gathered from hundreds of worldwide permanent receivers of the Global Navigation Satellite Systems, GNSS (like the Global Positioning System GPS), working many of them in real time. In this work we generalize GSFLAI for the very challenging scenario of stellar superflares, with a much weaker expected geoeffectiveness on the Earth ionosphere, making it difficult to distinguish its potential footprint regarding conventional ionospheric variability sources. Indeed, we will show that, unlike GSFLAI for solar flares, the new algorithm presented here (Blind GNSS search of Extraterrestrial EUV Sources [BGEES]) is able to detect EUV flares without the previous knowledge of the position of the source, which is also simultaneously estimated, providing an additional quality check of the detection. It will be first assessed with several case studies of solar flares of different intensities analyzed previously with GSFLAI. Finally, by focusing on the night hemisphere to avoid the Sun's larger effect on the ionosphere, the detection and location with BGEES of two recent stellar superflares, Proxima Centauri (18 March 2016, 08:32UT) and NGTS J121939.5‐355557 (1 February 2016, 04:00UT), are presented, strongly suggesting the extension and applicability of the new technique, also in real time.

Prompt and accurate imaging of the ionosphere is essential to space weather services, given a broad spectrum of applications that rely on ionospherically propagating radio signals. As the 3D spatial extent of the ionosphere is vast and covered only fragmentarily, data fusion is a strong candidate for solving imaging tasks. Data fusion has been used to blend models and observations for the integrated and consistent views of geosystems. In space weather scenarios, low latency of the sensor data availability is one of the strongest requirements that limits the selection of potential datasets for fusion. Since remote plasma sensing instrumentation for ionospheric weather is complex, scarce, and prone to unavoidable data noise, conventional 3D-var assimilative schemas are not optimal. We describe a novel substantially 4D data fusion service based on near-real-time data feeds from Global Ionosphere Radio Observatory (GIRO) and Global Navigation Satellite System (GNSS) called GAMBIT (Global Assimilative Model of the Bottomside Ionosphere with Topside estimate). GAMBIT operates with a few-minute latency, and it releases, among other data products, the anomaly maps of the effective slab thickness (EST) obtained by fusing GIRO and GNSS data. The anomaly EST mapping aids understanding of the vertical plasma restructuring during disturbed conditions.