In this study, midlatitude summer nighttime anomalies (MSNAs) are analyzed via observations and tidal/planetary wave features using measurements from the Formosat-3/Constellation Observing System for Meteorology, Ionosphere, and Climate (F3C) for 2007, a year with low solar activity, and 2014, a year with high solar activity. The total ionospheric electron content, $E{C}_{ion}$, an integrated quantity derived from F3C measurements, was used to compare the observational data. The $E{C}_{ion}$ values were derived from accurate radio-occultation-retrieved electron density profiles without assuming spherical symmetry and from a model that separated the ground total electron content into the plasmaspheric and the ionospheric electron content contributions. An analysis of the $E{C}_{ion}$ data set confirmed that MSNAs were present in three different regions of the world for the months surrounding the local summer solstice during both 2007 and 2014. In the southern hemisphere, the so-called Weddell Sea Anomaly showed a maximum increase in $E{C}_{ion}$, measured as the difference between nighttime and midday values, that was more than three times that in the northern MSNAs. For each individual MSNA, the corresponding maximum increases in electron content were similar between the two years analyzed, so they were not significantly affected by solar activity. Then, linear least-square fit to the frequency–wave number basis functions was used to derive the tidal and planetary wave components contributing to MSNAs. The main component that appears to produce the Weddell Sea Anomaly is D0, followed by SPW1, DW2, and DE1, in this order, which make secondary but still relevant contributions. The presence of MSNAs in the northern hemisphere was clearly supported by the migrating tide SW2 in combination with DE1. SW2 also supported an early morning MSNA being observed in the northern hemisphere. The main tidal and planetary wave signatures producing the MSNAs did not significantly differ between 2007 and 2014.

The customary procedure to compute the rate of total electron content index (ROTI) presents some limitations when using the geometry-free (GF) combination of Global Positioning System (GPS) L1 and L2 carriers tracked by geodetic receivers. First, the effect of the tracking strategy implemented by each receiver manufacturer to obtain the L2 carrier from code-less observations. Second, the impact of frequent cycle slips on the L2 carrier. These limitations hinder the monitoring and characterization of ionospheric scintillation. To overcome them, the present study proposes the calculation of ROTI from the individual (uncombined) L1 carrier-phase, ROTI_Ll , using the Geodetic Detrending (GD) post-processing methodology, in contrast to the conventional GF combination, ROTI_GF . The analysis of the entire year 2020 shows that those two aforementioned limitations produce inconsistent ROTI_GF values measured by pairs of close receivers from different manufacturers. In contrast, the distribution of ROTI_L1 values shows a full consistency between different receivers, being significantly less affected by cycle slips and allowing a valid and well-grounded identification of scintillation. The study concludes that ROTI_L1 , calculated using a 60 s window from geodetic receivers operating at 1 Hz, provides a robust tool to monitor and characterize ionospheric scintillation world-wide and regardless of the type of receiver. In particular, a ROTI_L1 threshold of 1.8 TECU/min is established as the minimum level of detectable scintillation in 2020, a year of low solar activity. The most intense scintillation periods in high-latitude regions are statistically characterized by the newly proposed ROTI_L1 .

A real-time (RT) ionospheric scintillation monitoring tool has been developed based on observations from geodetic receivers in Global Navigation Satellite System (GNSS) networks. It extends the application of the Geodetic Detrending (GD) technique to make it work with RT products for satellite orbit, tropospheric and satellite/receiver clock corrections applied to uncombined GNSS signals. It overcomes the limitation of the coverage of specialized ionospheric scintillation monitoring receivers (ISMRs), enabling worldwide monitoring. Through this novel tool, it is possible to supply large RT information about scintillation activity to both GNSS users and the scientific community. The performance of the tool has been validated by cross checking with post-processing GD results and reference data from a collocated ISMR in a period with intense scintillation activity. The results demonstrate high consistency for the phase scintillation index between the RT tool based on geodetic receivers operating at 1 Hz and the reference ISMR. The few outliers detected are related with the different processing, location and sampling frequency from each type of receiver.