Ionospheric day‐to‐day variability is ubiquitous, even under undisturbed geomagnetic and solar conditions. In this paper, quiet‐time day‐to‐day variability of equatorial vertical E × B drift is investigated using observations from ROCSAT‐1 satellite and the Whole Atmosphere Community Climate Model with thermosphere and ionosphere eXtension (WACCM‐X) v2.1 simulations. Both observations and model simulations illustrate that the day‐to‐day variability reaches the maximum at dawn, and the variability of dawn drift is largest around June solstice at ~90–180°W. However, there are significant challenges to reproduce the observed magnitude of the variability and the longitude distributions at other seasons. Using a standalone electro‐dynamo model, we find that the day‐to‐day variability of neutral winds in the E‐region (≤~130 km) is the primary driver of the day‐to‐day variability of dawn drift. Ionospheric conductivity modulates the drift variability responses to the E‐region wind variability, thereby determining its strength as well as its seasonal and longitudinal variations. Further, the day‐to‐day variability of dawn drift induced by individual tidal components of winds in June are examined: DW1, SW2, D0, and SW1 are the most important contributors.

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.

In this work, we examine the impact of increased anthropogenic emissions on equatorial plasma bubble (EPB) occurrence by modeling the growth rate of Rayleigh‐Taylor (R‐T) instability (), which is closely related to EPB generation. Using the global coupled ionosphere‐thermosphere‐electrodynamics model‐institute of geology and geophysics, Chinese Academy of Sciences model, is calculated under three different CO₂ emission levels. As CO₂ increases, significantly increases at low altitudes (<∼260 km) and decreases at high altitudes (>∼320 km). In the altitudes in between, increases (decreases) before (after) midnight. Longitudinal variability of the change is manifested apparently above ∼280 km, while it is insignificant for low altitudes. Term analysis revealed that changes in the gravity term and the electric‐field term are the main causes and that the neutral‐wind term is insignificant. The investigation indicates that increased anthropogenic emissions can change EPB occurrence and, in turn, the radio‐communication system and therefore influence modern technological systems, which is expected to be more serious in the future.

This paper proposes a new approach to obtain seasonal variations of global tides for the horizontal winds in the mesosphere and lower thermosphere region, based on daily tides derived from the global coverage of the TIMED Doppler Interferometer (TIDI) and the local‐time coverage of a meteor radar chain. The daily variations of different mesosphere and lower thermosphere tides are obtained taking advantage of empirical tidal mode (ETM), which is first derived from Global Scale Wave Model using empirical orthogonal function analysis. ETM displays latitudinal and vertical features of each tidal component in a realistic background atmosphere with dissipation effects. After fitting the observations by ETM day by day, the monthly mean of daily fitted results is then used to describe tidal monthly features. Seasonal variations of three major tidal components were found: DW1 in both zonal and meridional winds usually has two maxima around equinoxes, DE3 in zonal winds achieves their maximum in September, while that in meridional winds becomes strongest in February and November. SW2 in zonal winds reaches largest amplitudes in May in the southern hemisphere, and meridional winds has minor peaks in February and November in the northern hemisphere. At last, we superpose each tidal component with the same frequency to reconstruct the global diurnal and semidiurnal tidal winds. Comparing them with both of TIDI 60‐day average winds and outputs of Global Scale Wave Model model, similar characteristics and magnitudes indicate their consistency and confirm the reliability and feasibility of this new approach.

In the present work, daily variation of eastward propagating diurnal tide with zonal‐wave number 3 (DE3) is derived from joint analysis on observations from Thermosphere Ionosphere Mesosphere Energetics and Dynamics Doppler Interferometer and a meteor radar chain around meridian 120°E during years of 2012–2015 and 2018–2020 via a novel method. Together with empirical tidal modes (ETMs), which are based on the Global Scale Wave Model, daily DE3 in horizontal winds are extracted. ETMs characterize the two‐dimensionally latitude‐altitudinal tidal structure with consideration of tidal dissipation, and thus makes it possible to obtain the DE3 tide extending to pole‐to‐pole in latitudes and covering 80–140 km on altitudes. Quantitatively analyzing day‐to‐day variability of mesosphere and lower thermosphere DE3 reveals that the variation of tidal phase is the main contributor to the DE3 day‐to‐day variability for both zonal and meridional winds. The strength of tidal‐phase induced variability has a clear seasonal dependence that is strong around June and December solstices. Prominent semiannual oscillation (SAO) for zonal (∼16%) and meridional (∼24%) winds are revealed, and annual oscillation (AO) is superposed on the SAO for the DE3 in meridional winds (∼9%). Tidal‐phase induced variability is generally stronger in solar minima (2018–2020) than that in solar maxima (2013–2015). Furthermore, a comparison with simulations using the Whole Atmosphere Community Climate Model eXtended is discussed. The simulations confirm that the primary role of tidal‐phase variations on the day‐to‐day variability. The model does not reproduce the SAO as shown in observations, while the AO in meridional winds is simulated well.

To date, no natural media is available to derive the “ancient” ionosphere, so the current understanding of ionospheric long‐term trends mainly comes from analyzing ∼70 yr modern measurements supplemented by theoretical simulations. In this study, for the first time, we expanded the ionosphere simulation to the whole Holocene (9455 BCE to 2015 CE) using the Global Coupled Ionosphere‐Thermosphere‐Electrodynamics Model developed at the Institute of Geology and Geophysics, Chinese Academy of Sciences, driven by a realistic geomagnetic field, CO₂ level, and solar activity, all of which are a combination of ancient media derivations and modern observations. Through a series of control runs, we found that the ionospheric oscillation of the global mean profile is characterized by a nonlinear variation versus geomagnetic field effect, a decrease (increase) above (below) ∼200 km due to CO₂ increase, and violent oscillations in phase with changes in solar activity, with corresponding contributions of approximately 20%, 20%, and 60%, respectively. The CO₂ effect became nonnegligible and even more significant after ∼1800 CE. The solar activity effect is marked by a frequently occurring grand solar minimum. The ionospheric characteristics show linear variations versus the dipole moment of the geomagnetic field, the CO₂ level, and the F10.7 index, with the growth rate having significant local time and latitude variations. Our prediction shows that a 400 ppm CO₂ increase will cause a global mean decrease of 1.2 MHz in foF2, 34 km in hmF2, and 4 tecu in TEC, which will directly influence radio wave communication.