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The present study describes a spatial and temporal analysis of the ionospheric variability over the European sector during a major storm event from 23 to 24 March 2023. The analysis is mainly based on ionospheric characteristics such as foF2, hmF2 and Vertical Total Electron Content (VTEC) over ten Digisondes and co-located GNSS receivers. The event started at 12:00UT on 23 March as a positive ionospheric storm followed by a negative ionospheric storm to 04:00 UT on the next day SYM-H<-183nT. A notable latitude dependence of the ionospheric response is more prominent over the northern mid-latitude region attributed to the equatorward displacement of the Midlatitude Ionospheric Trough (MIT). To verify this hypothesis, Swarm latitudinal electron density profiles from in-situ Langmuir probe measurements over Europe were considered. These profiles demonstrate a clear MIT displacement from ∼65°N on 22 March to ∼55°N on 23 March with a subsequent recovery around ∼65°N on 25 March. [ABSTRACT FROM AUTHOR]

We demonstrate a simple method to estimate the direction of propagation of travelling ionospheric disturbances using in-situ electron density measurements in the topside ionosphere by exploiting the side-by-side flying configuration of Swarm A and C satellites. Corresponding cases of TIDs recorded on detrended GPS total electron content (TEC) maps over different continents are used to validate this approach. This simple method could be suitable to detect the direction of propagation of TID wavefronts over the ocean and the polar regions where ground-based GNSS stations are unavailable. [ABSTRACT FROM AUTHOR]

For the first time, we reconstructed global distribution of both the total electron content disturbance W index and TEC values for eight extreme storms (Dst < -250 nT) occurred before the epoch of GNSS observations in solar cycle 22. We created a model based on superposed epoch analysis of the training set of GIM-W maps of nine SC23 extreme storms. Global GIM-W index maps are calculated from 15-min UPC GIM-TEC (UQRG) as the logarithmic deviation of instantaneous TEC from the monthly median GIMMTEC empirical model. We introduced the storm phase metrics for main and recovery phases of the positive ionosphere disturbance (the WU-index), the negative disturbance (the WL-index) and the ring current (the Dst-index). The probabilistic forecasting model (Pmodel) for SC22 GIM-Wx maps is developed based on GIM-W maps of the SC23 training set. The storm phase distribution Fx for the eight SC22 extreme storms is calculated from the proxy time shift (lag) of peak WUmax and WLmin relative to Dstmin. Proxy GIM-TECx maps are calculated by adjusting the GIM-MTEC median to the GIM-Wx prediction. Validation of the technique based on data of UPC and JPL for four intense ionospheric storms showed a root-mean-square error less than 3 TECU. The proposed technique can be applied for both the past and future forecasting of GIM-W index and GIM-TEC maps. [ABSTRACT FROM AUTHOR]

The present study focuses on ionospheric F-layer critical parameters (foF2/hmF2) and Total Electron Content (TEC) by exploiting a long-term data (2009 to 2016) from Digisonde and Global Positioning System (GPS) receiver observations over a lower-middle latitude European location Nicosia, Cyprus (geographic 35° N, 33° E; magnetic dip. 32° N). Also, it adheres to evaluating the performances of global empirical standard International Reference Ionosphere (IRI-2016), Standard Plasmasphere Ionosphere Model (SPIM-2017/IRI-Plas 2017), and interpolated TEC from the IGS-Global Ionospheric Maps (GIMs) by comparing with the Digisonde and GPS observations. Our results confirm a noteworthy departure of estimated foF2/hmF2 and TEC in SPIM-2017, even larger than that of IRI-2016 as regards to the Digisonde and GPS observations, irrespective of season, solar activity, and geomagnetic activity conditions. This contradicts the general perception on an ideal behavior of the empirical climatological model over the middle latitude region, inferring that the transient region between the low and middle latitude does suffer from noticeable uncertainties. Also, we did not notice any convincing response of the storm sub-model in IRI except a rare flipping in its magnitude and absolutely no alteration in SPIM model estimations to the onset of geomagnetic storms over the region despite the storm sub-model was kept 'on'. This suggests a revisit into the underlying storm sub-model database in the models. Interestingly, the ingestion of Digisonde recorded foF2/hmF2 and GPS-TEC into the SPIM-2017 model results in a remarkable convergence of the parameters towards the local observations even during active geomagnetic storm conditions. It ascertains the flexibility in SPIM-2017 towards plausible improvements in the model estimations by ingesting GPS-TEC. Above all, such a scheme is in line with efforts towards reliable ionospheric error mitigations in navigation, communication, and satellite applications. [ABSTRACT FROM AUTHOR]

The critical frequency of ionospheric F2 layer (foF2) is a measure of the highest frequency of radio signal that may be reflected back by the F2 layer, and it is associated with ionospheric peak electron density in the F2 layer. Accurate long-term foF2 variations are usually derived from ionosonde observations. In this paper, we propose a new method to observe foF2 using a stand-alone global positioning system (GPS) receiver. The proposed method relies on the mathematical equation that relates foF2 to GPS observations. The equation is then implemented in the Kalman filter algorithm to estimate foF2 at every epoch of the observation (30-s rate). Unlike existing methods, the proposed method does not require any additional information from ionosonde observations and does not require any network of GPS receivers. It only requires as inputs the ionospheric scale height and the modeled plasmaspheric electron content, which practically can be derived from any existing ionospheric/plasmaspheric model. We applied the proposed method to estimate long-term variations of foF2 at three GPS stations located at the northern hemisphere (NICO, Cyprus), the southern hemisphere (STR1, Australia) and the south pole (SYOG, Antarctic). To assess the performance of the proposed method, we then compared the results against those derived by ionosonde observations and the International Reference Ionosphere (IRI) 2012 model. We found that, during the period of high solar activity (2011-2012), the values of absolute mean bias between foF2 derived by the proposed method and ionosonde observations are in the range of 0.2-0.5 MHz, while those during the period of low solar activity (2009-2010) are in the range of 0.05-0.15 MHz. Furthermore, the root-mean-square-error (RMSE) values during high and low solar activities are in the range of 0.8-0.9 MHz and of 0.6-0.7 MHz, respectively. We also noticed that the values of absolute mean bias and RMSE between foF2 derived by the proposed method and the IRI-2012 model are slightly larger than those between the proposed method and ionosonde observations. These results demonstrate that the proposed method can estimate foF2 with a comparable accuracy. Since the proposed method can estimate foF2 at every epoch of the observation, it therefore has promising applications for investigating various scales (from small to large) of foF2 irregularities. [ABSTRACT FROM AUTHOR]

Ionospheric TEC (Total Electron Content) variations prior to the deep (≈600 km) earthquake doublet close to magnetic equator in Peru ( M = 7.6) and to the intermediate (≈200 km) earthquake in Afghanistan ( M = 7.5) during 2015 were investigated using measurements from Global Navigation Satellite System (GNSS) network with the aim to detect possible ionospheric precursors of these events. For this we applied both statistical and spectral analysis. Ionospheric anomalies related to both earthquakes were observed few hours and few days prior to the earthquakes during daytime localized mainly near the epicenter. These were large-scale positive TEC anomalies and small-scale TEC oscillations with periods of 20 min and duration around 2–4 h appearing at the same local time each day. Several days prior to the earthquake in Peru a significant phenomenon was observed during afternoon time related to the modification of the Equatorial Ionization Anomaly (EIA) structure. During nighttime, however, it was not possible to identify any ionospheric earthquake precursor due to the concurrence of various phenomena, such as Equatorial Plasma Bubbles and pre- and post-midnight TEC peaks prior to Peru earthquake, and solar terminator transition prior to both earthquakes which could induce resembling ionospheric anomalies. [ABSTRACT FROM AUTHOR]

This paper presents a review on the PECASUS service, which provides advisories on enhanced space weather activity for civil aviation. The advisories are tailored according to the Standards and Recommended Practices of the International Civil Aviation Organization (ICAO). Advisories are disseminated in three impact areas: radiation levels at flight altitudes, GNSS-based navigation and positioning, and HF communication. The review, which is based on the experiences of the authors from two years of running pilot ICAO services, describes empirical models behind PECASUS products and lists ground- and space-based sensors, providing inputs for the models and 24/7 manual monitoring activities. As a concrete example of PECASUS performance, its products for a post-storm ionospheric F2-layer depression event are analyzed in more detail. As PECASUS models are particularly tailored to describe F2-layer thinning, they reproduce observations more accurately than the International Reference Ionosphere model (IRI(STORM)), but, on the other hand, it is recognized that the service performance is much affected by the coverage of its input data. Therefore, more efforts will be directed toward systematic measuring of the availability, timeliness and quality of the data provision in the next steps of the service development. [ABSTRACT FROM AUTHOR]

The objective of this article is to present a concept for single-frequency Global Navigation Satellite System (GNSS) positioning local ionospheric mitigation over a certain area. This concept is based on input parameters driving the NeQuick-G algorithm (the ionospheric single-frequency GNSS correction algorithm adopted by Galileo GNSS system), estimated on a local as opposed to a global scale, from ionospheric characteristics measured by a digital ionosonde and a collocated dual-frequency Total Electron Content (TEC) monitor. This approach facilitates the local adjustment of Committee Consultative for Ionospheric Radiowave propagation (CCIR) files and the Az ionization level, which control the ionospheric electron density profile in NeQuick-G, therefore enabling better estimation of positioning errors under quiet geomagnetic conditions. This novel concept for local ionospheric positioning error mitigation may be adopted at any location where ionospheric characteristics foF2 and M(3000)F2 can be measured, as a means to enhance the accuracy of single-frequency positioning applications based on the NeQuick-G algorithm. [ABSTRACT FROM AUTHOR]

The purpose of the present study is to investigate simultaneously pre-earthquake ionospheric and atmospheric disturbances by the application of different methodologies, with the ultimate aim to detect their possible link with the impending seismic event. Three large earthquakes in Mexico are selected (8.2 Mw, 7.1 Mw and 6.6 Mw during 8 and 19 September 2017 and 21 January 2016 respectively), while ionospheric variations during the entire year 2017 prior to 37 earthquakes are also examined. In particular, Total Electron Content (TEC) retrieved from Global Navigation Satellite System (GNSS) networks and Atmospheric Chemical Potential (ACP) variations extracted from an atmospheric model are analyzed by performing statistical and spectral analysis on TEC measurements with the aid of Global Ionospheric Maps (GIMs), Ionospheric Precursor Mask (IPM) methodology and time series and regional maps of ACP. It is found that both large and short scale ionospheric anomalies occurring from few hours to a few days prior to the seismic events may be linked to the forthcoming events and most of them are nearly concurrent with atmospheric anomalies happening during the same day. This analysis also highlights that even in low-latitude areas it is possible to discern pre-earthquake ionospheric disturbances possibly linked with the imminent seismic events. [ABSTRACT FROM AUTHOR]