One of the most popular indices for monitoring the occurrence and intensity of ionospheric L-band irregularities is the Rate of TEC Index (ROTI). Due to low TEC in the mid-latitude ionosphere, ROTI has received significantly less attention than the equatorial and polar ionosphere. On the other hand, spread F is an established ionogram irregularity signature. The present study aims to correlate ROTI and spread F activity over European Digisonde stations for a low-to-moderate solar activity year (2011). With a focus on the latitude-dependent occurrence, the analysis demonstrates that range spread F (RSF) has been identified for all notable ROTI (>0.15 TECU/min) cases which also coincide with MSTID activity over the stations, suggesting induced gravity waves or polarization electric fields as the driving mechanism for enhanced ROTI activity. The diurnal and seasonal features are also presented. Maximum irregularity occurrence was observed around the 45° N from 18:00 to 05:00 UT with the seasonal maximum occurrence in January. Over lower mid-latitude Digisonde stations (latitude < 45° N), the diurnal and seasonal occurrence was observed from 19:00 to 04:30 UT in July.

A major earthquake with a magnitude of M _W = 7.7, followed by several aftershocks, occurred in Mandalay, Myanmar, on 28 March 2025. This study aims to report on the co‐seismic ionospheric disturbances caused by the event, based on a multi‐instrument approach that was adopted to examine co‐seismic effects. Frequency analysis and filtering techniques were employed to distinguish between different acoustic or gravity wave signatures in the ionosphere. Ground seismic stations provided wave velocity estimation, while the velocity of co‐seismic ionospheric wavefronts was estimated using Total Electron Content fluctuations from GNSS receivers. Using the collocation of a seismic station with an Ionosonde station, it has been possible to estimate the vertical propagation time of acoustic waves, resulting in multi‐cusp signature formation. Additionally, radio occultation electron density profiles from the COSMIC‐2 mission have been analyzed in search of topside signatures. While horizontal velocities of co‐seismic ionospheric wavefronts were estimated between 0.8 and 3.6 km/s, their non‐isotropic distribution with epicentral distance revealed information about the background generation mechanism. For each seismic event, studies related to the co‐seismic ionospheric behavior could provide insightful information relating the coupling between ground and upper atmosphere. This study exploits a combination of data sets for a comprehensive understanding of the ionospheric disturbances associated with an earthquake.

This study investigates the diurnal, seasonal, and latitudinal variations of Spread F and the Rate of TEC Index (ROTI) over North America during the high solar activity period of 2014. Using GNSS-based ROTI measurements and Digisonde ionograms from multiple stations, we systematically analyze the relationship between Spread F occurrences and ROTI enhancements. The analysis incorporated Diurnal and seasonal variations to determine dominant trends and potential driving mechanisms, such as medium-scale traveling ionospheric disturbances (MSTIDs) and polarization electric fields. Seasonal and latitudinal variations of Spread F occurrences and ROTI fluctuations are found to be strongly linked to MSTIDs and geomagnetic activity. A clear seasonal dependence was observed at the stations situated under the transitional and mid-latitude regions of the ionosphere. The maximum irregularity occurred in April for transitional region stations and in November for mid-latitudinal stations. Additionally, Spread F and ROTI exhibit similar diurnal and seasonal trends, with maximum irregularity occurrences during nighttime (20:00–02:00 LT). A distinct seasonal dependence is observed, with transitional region stations peaking in winter and mid-latitude stations in summer. Notably, spread F was consistently associated with notable ROTI values (>0.15 TECU/min), suggesting gravity waves and polarization electric fields as driving mechanisms. Through detailed case studies, we demonstrated that MSTIDs, likely driven by gravity wave dynamics, play a crucial role in generating plasma irregularities, which in turn enhance ROTI values and contribute to Spread F formation. Under quiet geomagnetic conditions, these irregularities exhibit a strong daytime preference. Conversely, during disturbed geomagnetic conditions (e.g., the geomagnetic storm), the spatial extent of ionospheric irregularities increased significantly, affecting both transitional and mid-latitude stations for both daytime and nighttime. By demonstrating a persistent relationship between Spread F and ROTI, this study advances ionospheric modelling efforts and supports the development of improved space weather forecasting techniques, crucial for GNSS-based navigation and communication systems.