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Abstract This study characterizes the main ionospheric trough (MIT) using a newly implemented detection method applied to ground‐based Global Navigation Satellite System data. The MIT is a region of plasma depletion occurring primarily in the nighttime sub‐auroral F‐region ionosphere. Analysis is based on ground‐based ionosphere total electron content (TEC) measurements from 2012 to 2024 and is applied to both hemispheres. The data are sorted by geomagnetic condition and season. We characterize MIT dynamics and compare the results with previous studies. Detection algorithm limitations, hemispheric asymmetry, trough depth, boundary wall steepness and position are statistically quantified and visualized. Main conclusions include: (a) Automatic trough detection is highest during geomagnetically active winter in the northern hemisphere (NH). (b) This detection method creates synoptic views of the trough which we can use to demonstrate control of sub‐auroral polarization streams (SAPS) over the dusk/afternoon sector and influence of storm onset on the MIT. (c) There is a noticeable morning preference for the southern hemisphere (SH) trough. (d) The dawn‐side SH trough appears equatorward relative to the NH, potentially due to influence from polar convection patterns. The dusk‐side NH trough appears slightly equatorward of the SH trough as a response to SAPS. (e) The deepest trough occurs during dawn hours and demonstrates more consistent longitudinal patterns during quiet local winter. (f) The steepest trough boundary is at the poleward wall with a positive gradient at 12–15 local time in NH summer. Synoptic maps illustrate asymmetries in the trough structure and the influence of density plumes. 

Abstract This study investigates impacts of the May 2024 superstorm on the mid‐latitude Global Positioning System (GPS) scintillation and position errors. Using 1‐Hz GPS receiver data, we identified position errors in PPP mode reaching up to 70 m in the Central United States during the storm main phase on May 10. The PPK solution becomes unstable following the arrival of storm and lasted till the recovery phase, coinciding with reported GPS outages of farming equipment. The large position errors were attributed to strong scintillation and carrier phase cycle slips around the equatorward boundary of the ionosphere trough, where large total electron content (TEC) gradients and irregularities were present. In the Southwestern United States, position errors of 10–20 m were associated with the storm‐enhanced density and equatorial ionization anomaly. Scintillation and cycle slips in this region were minor, and bending of the GPS signal paths (refractive effect) is suggested to cause the position errors. PPP outages were also associated with sudden changes in the geometric distributions of available GPS satellites used in position calculations. On May 11, energetic particle precipitation during substorms led to abrupt jumps in TEC and scintillation, resulting in rapidly evolving position errors of up to 10 m. These findings highlight the critical role of storm‐time plasma transport, precipitation, and irregularity formation in degrading GPS performance. The study underscores the need for accurate ionospheric state specification, improved signal processing technique, real‐time ionospheric corrections, and optimized satellite selection algorithms, to enhance navigation resilience during severe space weather events. 

The great American total solar eclipse of 21 August 2017 offered a fortuitous opportunity to study the response of the atmosphere and ionosphere using a myriad of ground instruments. We have used the network of U.S. Global Positioning System receivers to examine perturbations in maps of ionospheric total electron content (TEC). Coherent large-scale variations in TEC have been interpreted by others as gravity wave-induced traveling ionospheric disturbances. However, the solar disk had two active regions at that time, one near the center of the disk and one at the edge, which resulted in an irregular illumination pattern in the extreme ultraviolet (EUV)/X-ray bands. Using detailed EUV occultation maps calculated from the National Aeronautics and Space Administration Solar Dynamics Observatory Atmospheric Imaging Assembly images, we show excellent agreement between TEC perturbations and computed gradients in EUV illumination. The results strongly suggest that prominent large-scale TEC disturbances were consequences of direct EUV modulation, rather than gravity wave-induced traveling ionospheric disturbances. 

Abstract The impacts of solar eclipses on the ionosphere‐thermosphere system particularly the composition, density, and transport are studied using numerical simulation and subsequent model‐data comparison. We introduce a newly developed model of a solar eclipse mask (shadow) at extreme ultraviolet (EUV) wavelengths—PyEclipse—that computes the corresponding shadowing as a function of space, time, and wavelength of the input solar image. The current model includes interfaces for Solar Dynamics Observatory and Geostationary Operational Environmental Satellites EUV telescopes providing solar images at nine different wavelengths. We show the significance of the EUV eclipse shadow spatial variability and that it varies significantly with wavelength owing to the highly variable solar coronal emissions. We demonstrate geometrical differences between the EUV eclipse shadow compared to a geometrically symmetric simplification revealing changes in occultation vary ±20%. The EUV eclipse mask is validated with in situ solar flux measurements by the PRoject for Onboard Autonomy 2/Large Yield Radiometer instrument suite showing the model captures the morphology and amplitudes of transient variability while the modeled gradients are slower. The effects of spatially EUV eclipse masks are investigated with Global Ionosphere Thermosphere Model for the 21 August 2017 eclipse. The results reveal that the modeled EUV eclipse mask, in comparison with the geometrically symmetric approximation, causes changes in the Total Electron Content in order of ±20%, 5%–20% in F‐region plasma drift, and 20%–30% in F‐region neutral winds. 

Abstract We present observations that show structured diffuse aurora (SDA) correlated with electron precipitation directly from the outer boundary of the outer radiation belt. The SDA maps to the nightside transition region (∼9–12R_E) in the magnetic‐equatorial plane during a substorm growth phase. The energy flux of 100‐ to 300‐keV electrons lost from the outer boundary of the radiation belt is ∼0.4 mW/m², which is comparable to electron dropouts >100 keV during magnetic storms. The latitudinal dispersion of energetic electrons observed in the ionosphere with energetic electrons more equatorward suggests nonadiabatic scattering from a thinning current sheet. The GLobal airglOW (GLOW) model shows significant optical contributions (up to 46%) from electrons >30 keV within the SDA. Ground‐ and space‐based measurements are consistent with the conclusion that the SDA marks the outer radiation belt boundary during substorm growth phase.