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Abstract Low‐cost instrumentation combined with volunteering and citizen science educational initiatives allowed the deployment of L‐band scintillation monitors to remote sense areas that are geomagnetically conjugated and located at low‐to‐mid latitudes in the American sector (Quebradillas in Puerto Rico and Santa Maria in Brazil). On 10 and 11 October, 2023, both monitors detected severe scintillations, some reaching dip latitudes beyond 26°N. The observations show conjugacy in the spatio‐temporal evolution of the scintillation‐causing irregularities. With the aid of collocated all‐sky airglow imager observations, it was shown that the observed scintillation event was caused by extreme equatorial plasma bubbles (EPBs) reaching geomagnetic apex altitudes exceeding 2,200 km. The observations suggest that geomagnetic conjugate large‐scale structures produced conditions for the development of intermediate scale (few 100 s of meters) in both hemispheres, leading to scintillation at conjugate locations. Finally, unlike previous reports, it is shown that the extreme EPBs‐driven scintillation reported here developed under geomagnetically quiet conditions. 

Abstract Signals recorded by two stations in the Brazilian region: [Fortaleza (3.74°S, 38.57°W) and Inconfidentes (22.31°S, 46.32°W)], receiving L1 transmissions from different geostationary satellites, were used to evaluate the amplitude scintillation indexS₄and several characteristics of scintillation events (continuous record withS₄ > 0.2) during nighttime hours (18:00 LT–02:00 LT) in the years 2014–2016. The effects from solar activity, season, and local time on the number of scintillation events per night, maximum scintillation, scintillation event duration, and spacing between consecutive events will be discussed. The results indicate that: (a) scintillation occurs from September to March in both links; (b) the most likely numbers of observed scintillation events per night were two or three, particularly during the first 2 years; (c) on average, the first scintillation event usually had larger maximumS₄values when compared to those of the later ones along the night; (d) the first scintillation event had a longer mean duration than the succeeding ones in a given night; (e) the durations of scintillation events, regardless of their numbers per night and the location, decreased with local time; (f) the opposite dependence of spacings between consecutive events on local time was observed; (g) the cumulative distribution functions of the scintillation onset time indicated a strong dependence on the dip latitude of the station; and (h) early occurrences of onset times are directly related to the increased probability of the occurrence of multiple scintillation events. 

Abstract We describe a mode for two-dimensional UHF (445 MHz) radar observations ofF-region irregularities using the 14-panel version of the advanced modular incoherent scatter radar (AMISR-14). We also present and discuss examples of observations made by this mode. AMISR-14 is installed at the Jicamarca Radio Observatory (JRO, 11.95°S, 76.87°W, ~ 0.5° dip latitude) in Peru and, therefore, allows studies of ionospheric irregularities at the magnetic equator. The new mode takes advantage of the electronic beam-steering capability of the system to scan the equatorialF-region in the east–west direction. Therefore, it produces two-dimensional views of the spatial distribution of sub-meter field-aligned density irregularities in the magnetic equatorial plane. The scans have a temporal resolution of 20 s and allow observations over a zonal distance of approximately 400 km at mainF-region heights. While the system has a lower angular and range resolution than interferometric in-beam VHF radar imaging observations available at Jicamarca, it allows a wider field-of-view than that allowed with the VHF system. Here, we describe the mode, and present and discuss examples of observations made with the system. We also discuss implications of these observations for studies of ESF at the JRO. Graphical abstract 

Abstract The 14‐panel Advanced Modular Incoherent Scatter Radar (AMISR‐14) system deployed at Jicamarca observed equatorial spread F plumes on two consecutive nights under unfavorable seasonal and solar flux conditions during a period that can be categorized as geomagnetically quiet. The AMISR‐14 capability of observing in multiple pointing directions allowed the characterization of the irregularity zonal drifts revealing that, in addition to their atypical occurrence, the zonal drifts of these plumes/irregularities also presented distinct patterns from one night to another, reversing from east to west on the second night. This work addresses two main subjects: (a) the mechanisms that may have led to the generation of these irregularities, despite the unfavorable conditions, and (b) the mechanisms that possibly led to the reversal (east‐to‐west) in the zonal plasma drift on the second night. To do so a multi‐instrumented and multi‐location investigation was performed. The results indicate the occurrence of simultaneous spread‐F events over the Peruvian and the Brazilian regions, evidencing a non‐local process favoring the development of the irregularities. The results also suggest that, even under very mild geomagnetic perturbation conditions, the recurring penetration of electric fields in the equatorial ionosphere can occur promptly, modifying the equatorial electrodynamics and providing favorable conditions for the plume development. Moreover, the results confirm that the eastward penetration electric fields, combined with the upsurge of Hall conductivity in the nighttime typically associated with the presence of sporadic‐E layers, are likely to be the mechanism leading to the reversal in the irregularity zonal drifts over these regions. 

Abstract Ionospheric scintillation and fading events over low‐latitude regions are often caused by severely depleted geomagnetic field‐aligned structures known as Equatorial Plasma Bubbles. These events are subject of interest to scientific investigations and concern to technological applications. Over the past several years, most of scintillation studies have focused on the dependence of these events on density gradients, location, local time, geomagnetic conditions, and so forth. This work presents a discussion about the role of the alignment between the signal propagation path and the depleted structures or, equivalently, the geomagnetic field lines, on the observed scintillation and deep fading characteristics. Data from three stations (dip latitudes: 16.13°S, 19.87°S, and 22.05°S) located around the Equatorial Ionization Anomaly (EIA) region were used to assess the amplitude scintillation severity and the deep fading events features under aligned and nonaligned conditions. The results show that the alignment condition plays a crucial role in the occurrence of strong scintillation. The study also revealed that, as stations far from the crests of the EIA are considered, the alignment influence seems to increase, and that a combination of strong plasma density fluctuation and increased aligned path is, presumably, the configuration under which the most severe scintillation and drastic deep fading events are observed. The results indicate that this conjunction is typically met in regions somewhat distinct from that with largest plasma density background over the Brazilian region, therefore, strongest scintillation and largest deep fading rates were observed by a station slightly off‐the EIA peak. 

Abstract The occurrence of plasma irregularities and ionospheric scintillation over the Caribbean region have been reported in previous studies, but a better understanding of the source and conditions leading to these events is still needed. In December 2021, three ground-based ionospheric scintillation and Total Electron Content monitors were installed at different locations over Puerto Rico to better understand the occurrence of ionospheric irregularities in the region and to quantify their impact on transionospheric signals. Here, the findings for an event that occurred on March 13–14, 2022 are reported. The measurements made by the ground-based instrumentation indicated that ionospheric irregularities and scintillation originated at low latitudes and propagated, subsequently, to mid-latitudes. Imaging of the ionospheric F-region over a wide range of latitudes provided by the GOLD mission confirmed, unequivocally, that the observed irregularities and the scintillation were indeed caused by extreme equatorial plasma bubbles, that is, bubbles that reach abnormally high apex heights. The joint ground- and space-based observations show that plasma bubbles reached apex heights exceeding 2600 km and magnetic dip latitudes beyond 28 ° . In addition to the identification of extreme plasma bubbles as the source of the ionospheric perturbations over low-to-mid latitudes, GOLD observations also provided experimental evidence of the background ionospheric conditions leading to the abnormally high rise of the plasma bubbles and to severe L-band scintillation. These conditions are in good agreement with the theoretical hypothesis previously proposed. Graphical Abstract 

We introduce the implementation of a global climatological model of the equatorial ionospheric F-region zonal drifts (EZDrifts) that is made available to the public. The model uses the analytic description of the zonal plasma drifts presented by Haerendel et al. (1992) [ J Geophys Res 97(A2) : 1209–1223] and is driven by climatological models of the ionosphere and thermosphere under a realistic geomagnetic field configuration. EZDrifts is an expansion of the model of the zonal drifts first presented by Shidler & Rodrigues (2021) [ Prog Earth Planet Sci 8 : 26] which was only valid for the Jicamarca longitude sector and two specific solar flux conditions. EZDrifts now uses vertical equatorial plasma drifts from Scherliess & Fejer (1999) [ J Geophys Res 104(A4) : 6829–6842] model which allows it to provide zonal drifts for any day of the year, longitude, and solar flux condition. We show that the model can reproduce the main results of the Shidler & Rodrigues (2021) [ Prog Earth Planet Sci 8 : 26] model for the Peruvian sector. We also illustrate an application of EZDrifts by presenting and discussing longitudinal variabilities produced by the model. We show that the model predicts longitudinal variations in the reversal times of the drifts that are in good agreement with observations made by C/NOFS. EZDrifts also predicts longitudinal variations in the magnitude of the drifts that can be identified in the June solstice observations made by C/NOFS. We also point out data-model differences observed during Equinox and December solstice. Finally, we explain that the longitudinal variations in the zonal plasma drifts are caused by longitudinal variations in the latitude of the magnetic equator and, consequently, in the wind dynamo contributing to the resulting drifts. EZDrifts is distributed to the community through a public repository and can be used in applications requiring an estimate of the overall behavior of the equatorial zonal drifts. 

The low-latitude ionosphere has an active behavior causing the total electron content (TEC) to vary spatially and temporally very dynamically. The solar activity and the geomagnetic field have a strong influence over the spatiotemporal distribution of TEC. These facts make it a challenge to attempt modeling the ionization response. Single frequency GNSS users are particularly vulnerable due to these ionospheric variations that cause degradation of positioning performance. Motivated by recent applications of machine learning, temporal series of TEC available in map formats were employed to build an independent TEC estimator model for low-latitude environments. A TEC dataset was applied along with geophysical indices of solar flux and magnetic activity to train a feedforward artificial neural network based on a multilayer perceptron (MLP) approach. The forecast for the next 24 h was made relying on TEC maps over the Brazilian region using data collected on the previous 5 days. The performance of this approach was evaluated and compared with real data. The accuracy of the model was evaluated taking into account seasonality, spatial coverage and dependence on solar flux and geomagnetic activity indices. The results of the analysis show that the developed model has a superior capacity describing the TEC behavior across Brazil, when compared to global ionosphere maps and the NeQuick G model. TEC predictions were applied in single point positioning. The achieved errors were 27% and 33% lower when compared to the results obtained using the NeQuick G and global ionosphere maps, respectively, showing success in estimating TEC with small recent datasets using MLP.