We investigate the ionospheric response to the 21 June 2020 annular solar eclipse using the multiinstrument observations including ionosondes, Global Navigation Satellite System (GNNS) receivers, COSMIC2, and DMSP and SWARM satellites. During the course of the eclipse, total electron content (TEC) decreased slightly in the morning at 20–70°E and largely in the afternoon at 80–150°E. However, maximum TEC depletion did not occur at the maximum obscuration, but stayed close to the southern edge of the running totality during the eclipse and near the northern edge of the elapsed totality after the eclipse. NmF2 showed the similar variation as TEC around 110°E. Meanwhile, a northward disturbance field‐aligned plasma drift was observed in the eclipse region and the disturbance became strong in the southern side of the totality around 120°E. The TEC and Swarm data revealed that the crests of the equatorial ionization anomaly (EIA) enhanced on both sides of the equator around noon in ~50–100°E although the northern crest was still in the Moon's shadow. The COSMIC2 profiles displayed the enhanced electron density in ~300–500 km altitudes and decreased density below ~300 km altitudes around the EIA crests in ~70°E. The Swarm observations recorded a drop in the electron temperature both in eclipse region and in conjugate hemisphere in 77°E and 96°E. The combined effect from the electric field, neutral wind, thermal conduction, and interhemispheric photoelectron transport might result in the complicated space and time variations of ionospheric responses to the eclipse.

The low‐latitude ionospheric TEC observed by the Beidou geostationary satellite showed large enhancement during 27–30 August 2018 of the storm recovery phase. The cause of the positive ionospheric storm during the recovery phase has yet to be resolved. In this study, multiple observations, including aurora, high‐latitude convection, potential, and the TEC maps, were used to study the contributions from the high‐speed solar wind to the ionosphere during the recovery phase of the storm. It was found that the high‐speed solar wind was effective in modulating the intensity and the size of the auroral oval, high‐latitude convection, and potential pattern. The Thermosphere Ionosphere Electrodynamics General Circulation Model generally reproduced the observed evolution of the ionosphere at high latitudes during the recovery phase of the storm, and it was used to quantitatively investigate the effects of the high‐speed solar wind on the recovery phase ionosphere. The results suggested that the high‐speed solar wind caused increase of TEC at auroral oval was about 2 TECU. The high‐speed solar wind, combined with oscillating interplanetary magnetic field Bz, led to the enhancement of the low‐latitude prompt penetrating electric fields and increased the low‐latitude TEC of about 2 TECU. Therefore, the high‐speed solar wind was a possible driver to the ionospheric positive storm during the recovery phase, but the causes for the more than 10‐TECU enhancement at low and middle latitudes during the recovery phase of this event are unknown.

• A north-south hemispheric difference in the ionosphere and thermosphere was observed, notably in the Asian and American sectors, during the May 2024 superstorm. • The north-south hemispheric difference in the total electron content (TEC) was strongly influenced by the thermospheric composition, density, and wind. • The plasma transport from the topside or conjugate hemispheres is important in modulating north-south hemispheric differences in the TEC.

In this study, the ionospheric responses in the Asian‐Australian, American, and African sectors during the August 2018 geomagnetic storm were investigated based on the Beidou geostationary orbit (GEO) satellite and Massachusetts Institute of Technology (MIT) Madrigal total electron contents (TECs), combined with measurements from ionosondes, magnetometers, and Global Ultraviolet Imager (GUVI). The middle‐ and low‐latitude TECs were dominated by positive responses over the three longitudinal sectors during the storm on 26–29 August. It is unique that daytime TECs at the Asian‐Australian, American, and African sectors displayed large enhancements larger than 10 TEC units (TECu) on 27–29 August, during the recovery phase, when the ionosphere is usually dominated by plasma depletions due to the ionospheric disturbance dynamo and/or disturbed thermospheric compositions. The combination and competition of the disturbed vertical plasma drifts through the solar wind‐magnetosphere‐ionosphere (SW‐M‐I) coupling and disturbed neutral compositions contribute significantly to the daytime TEC responses at different longitudinal sectors on 26 August during the main and early recovery phases. The eastward equatorial electrojet and O/N₂ during the recovery phase on 27–29 August are larger than the quiet reference, which suggest that the enhanced upward vertical plasma drifts combining with higher O/N₂ make an important contribution on the daytime positive ionospheric storm during the recovery phase. The enhanced vertical plasma drifts could not be driven by the SW‐M‐I coupling or ionospheric disturbance dynamo associated with the geomagnetic storm. Further studies should be untaken to explore the dominant sources for the enhanced upward vertical drifts during the recovery phase.

Scale height measures the altitude gradient of the electron density profile and relates with the ionospheric chemistry and dynamics, while its longitudinal variation has not been fully investigated in both statistical analyses and empirical modelings. In this study, 11‐year electron density profiles from Constellation Observing System for Meteorology, Ionosphere, and Climate radio occultations are collected to retrieve the α‐Chapman scale height (Hm) from the lower topside ionospheric electron density profile (within 200‐km altitudes above the peak height of F2 layer [hmF2]) by fitting α‐Chapman function with a constant scale height. The Hm shows evident longitudinal variations at midlatitudes, and its zonal structure shows a consistency with that of hmF2 during daytime, which indicates neutral winds change the ionospheric height and shape at the same time. Further, a global modeling of Hm named 2PCAFourier‐Hm is built based on a two‐layer Principle Component Analysis combined with Fourier regression analysis of its coefficients under low and moderated solar activity. Longitudinal variation is considered in the Hm's modeling, along with the variations of local time, latitude, day of the year, and solar activity. Overall, the model well captures the temporal and spatial variations of Hm with a root‐mean‐square error of 2.25 km and a correlation coefficient of 0.97 with respect to the Constellation Observing System for Meteorology, Ionosphere, and Climate observations.