On 10 May 2024 at 17 h:07 UTC, the simultaneous arrival of several solar coronal mass ejections (CMEs) generated the strongest geomagnetic storm of the last twenty years, with a minimum Dst = −412 nT, usually referred to as the Mother’s Day event. On 10 October 2024, the second strongest event of solar cycle 25 appeared with a Dst = −335 nT, preceded on 8 October by an event with a Dst = −153 nT. In the present work, with measurements of the vertical total electron content and with ionosonde observations from Europe, USA, and South Korea, we show that the ionization of the upper atmosphere shortly increased at the arrival of the CME for these different events, followed by a fast decrease at all latitudes. The ionization remained very low for more than a full day. While the recovery started at the beginning of the second day after the onset for both events in October, the sudden recovery in the middle of the second day on 12 May is much more unusual. The analysis of the observations at different latitudes and longitudes shows that the causes of the ionization variations during the superstorms were mainly due to strong perturbations in the ionospheric F layer, amplified by the plasmasphere’s influence on the vertical total electron content (VTEC). The erosion of the plasmasphere during these two strong events led to a plasmapause located at exceptionally low radial distances smaller than 2 Re (Earth’s radii) in the post-midnight sector and a rotating plume in the afternoon–dusk sector clearly visible in the BSPM plasmasphere model. It took several days after the storms to recover normal ionization rates.

The present study examines the negative ionospheric response over Europe during two geomagnetic storms on 10–13 May 2024, known as the Mother’s Day geomagnetic superstorm. The first storm, with a peak SYM-H value of −436 nT, occurred in the interval 10–11 May, while the second, less intense storm (SYM-H~−103 nT), followed in the interval 12–13 May. Using data from four European locations, temporal and spatial variations in ionospheric parameters (TEC, foF2, and hmF2) were analyzed to investigate the morphology of the strong negative response. Sharp electron density (Ne) depletion is associated with the equatorward displacement of the Midlatitude Ionospheric Trough (MIT), confirmed by Swarm satellite data. A key finding was the absence of foF2 and hmF2 values over all ionosonde stations during the recovery phase of the storms, likely due to the coupling between the Equatorial Ionization Anomaly (EIA) crests and the auroral ionosphere influenced by the intense uplift of the F layer. Relevant distinct features such as Large-scale Travelling Ionospheric Disturbance (LSTID) signatures and Spread F were also noted, particularly during the initial and main phase of the first storm over high midlatitude regions. Regional effects varied, with high European midlatitudes exhibiting different features compared to lower European latitude areas.

Acquiring reliable estimates of the Antarctic Ice Sheet surface mass balance is essential for trustworthy predictions of its evolution and future contribution to sea level rise. Snow height variations, i.e., the net change of the surface elevation resulting from a combination of surface processes such as snowfall, ablation, and wind redistribution, can provide a unique tool to constrain the uncertainty on mass budget estimations. In this study, GNSS Interferometric Reflectometry (GNSS-IR) is exploited to assess the long-term variations of snow accumulation and ablation processes. Eight antennas belonging to the Polar Earth Observing Network (POLENET) network are considered, together with the ROB1 antenna, deployed in the east part of Antarctica by the Royal Observatory of Belgium. For ROB1, which is located on an ice rise, we highlight an annual variation of snow accumulation in April–May (~30–50 cm) and ablation during spring/summer period. A snow surface elevation velocity of +0.08 ± 0.01 ma${}^{-1}$ is observed in the 2013–2016 period, statistically rejecting the “no trend” null hypothesis. As the POLENET stations are all located on moving glaciers, their associated downhill motion must be corrected for using an elevation model. This induces an increased uncertainty on the snow surface elevation change determined from GNSS-IR. Among the eight stations analyzed, only three of them show a long-term snow height variation larger than the uncertainties. One is located on the Flask Galcier in the Antarctic Peninsula, with a decrease of more than 4 m between 2012 and 2014, with an uncertainty of 2.5 m. The second one is located on the Lower Thwaites Glacier where we observe, between 2010 and 2020, a snow surface drop of 10 m, with a conservative uncertainty of 1 m. The third station, located on the West Antarctic Ice Sheet (WAIS) divide, shows on the opposite an upward motion from 2005 to 2019, of 1.2 m with an uncertainty of 0.4 m. The snow surface change of the other POLENET stations analyzed is smaller than the uncertainty associated with the glacier slope.

On 10 May 2024 at 17h:07 UTC, the arrival of solar a coronal mass ejection (CME) generated the strongest geomagnetic storm of the last twenty years with a minimum Dst = -412 nT, usually referred to as the Mother’s Day event. On 10 October 2024, the second strongest event of the solar cycle 25 appeared with Dst=-335 nT, preceded on 8 October by an event with Dst=-153nT. In the present work, we show with measurements of vertical total electron contents and with ionosonde observations from Europe, USA and South Korea that the ionization of the upper atmosphere shortly increased at the arrival of the CME for these different events, followed by a fast decrease at all latitudes. The ionization remained very low for more than a full day. While the recovery appears at the beginning of the second day after the onset for both events in October, the sudden recovery in the middle of the second day on 12 May is much more unusual. The analysis of the observations at different latitudes and longitudes shows that the causes of the ionization variations during the superstorms were mainly due strong perturbations in the ionospheric F layer, and amplified by the plasmasphere’s influence on the vertical total electron content (VTEC). The erosion of the plasmasphere during these two strong events led to a plasmapause located to exceptionally low radial distances smaller than 2 Re (Earth’s radii) in the post-midnight sector, and a rotating plume in the afternoon-dusk sector clearly visible in the BSPM plasmasphere model. Several days after the storms were necessary to recover normal ionization rates.

Intense solar radio bursts (SRBs) emitted at L-band frequencies are a source of radio frequency interference for Global Navigation Satellite Systems (GNSS) by inducing a noise increase in GNSS measurements, and hence degrading the carrier-to-noise density (C/N0). Such space weather events are critical for GNSS-based applications requiring real-time high-precision positioning.Since 2015, the Royal Observatory of Belgium (ROB) monitors in near real-time the C/N0 observations from the European Permanent Network (EPN). The monitoring allows to detect accurately the general fades of C/N0 due to SRBs over Europe as from 1 dB-Hz. It provides in near real-time a quantification of the GNSS signal reception fade for the L1 C/A and L2 P(Y) signals and notifies civilian single and double frequency users with a 4-level index corresponding to the potential impact on their applications. This service is part of the real-time monitoring service of the PECASUS project of the International Civil Aviation Organization (ICAO) which started end of 2019.Results of this 5-year monitoring will be discussed, including the 3 SRBs of 2015 and 2017, together with the new developments toward a global index using the International GNSS Service (IGS) network. In addition, we will show how the SRB monitoring is sometimes interfered by GPS flex power campaigns on the satellites from blocks IIR-M and IIF, and how it is mitigated . The routine and transient GPS flex power campaigns will be presented in terms of C/N0 variations for the EPN and IGS networks.

We present our work at the Royal Observatory of Belgium to develop a novel, data-driven approach to generate global near real-time VTEC maps using multi-constellation GNSS data, extending the capabilities of the established ROB-IONO software (Bergeot et al., 2014). Our method employs a multi-step downsampling and data reduction algorithm, combined with median polish kriging, to produce global VTEC maps. This purely data-driven approach, which does not rely on ionospheric models or prior time steps as input, enables near real-time mapping and robust analysis of large-scale ionospheric and plasmaspheric trends.These maps are particularly valuable for studying the ionosphere-plasmasphere system during geomagnetic storms and other disturbed conditions, such as the May 2024 geomagnetic storm. By integrating complementary datasets (e.g., COSMIC-2, ionosondes), we can disentangle ionospheric and plasmaspheric contributions to VTEC, offering new insights into their dynamic behavior and changes in distribution during space weather events. The downsampling and median polishing techniques also enable future analysis of long-term GNSS datasets, facilitating studies of decadal-scale trends in the ionosphere-plasmasphere system, which are critical for understanding changes in the climatology of the upper atmosphere and the impacts of solar cycle variations. This global VTEC mapping capability not only enhances space weather monitoring but also provides a powerful tool for investigating long-term ionospheric variability, with uses for both scientific research and operational applications.