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The intensity of the equatorial electrojet (EEJ) derived from the magnetic field measurements by the China Seismo-Electromagnetic Satellite (CSES) is analyzed for the low solar activity period of July 2018–April 2022. The CSES spacecraft flies in a Sun-synchronous orbit, providing the first continuous satellite observations of the afternoon EEJ at a fixed local time at 2 p.m. The EEJ intensities from CSES and concurrent observations from the Swarm satellite mission show a good correlation, supporting the reliability of the CSES EEJ data. Spectral analysis of the CSES data reveals the presence of three distinct oscillatory components in the day-to-day variation of the afternoon EEJ: (1) an eastward-propagating 2–3-day oscillation with zonal wavenumber 1, (2) a westward-propagating 5–6-day oscillation with zonal wavenumber 1, and (3) a zonally-symmetric 14–15-day oscillation. These oscillations result from upward-propagating waves in the atmosphere. That is, the first two can be attributed to the ultra-fast Kelvin wave and quasi-6-day wave, respectively, while the latter is likely due to the atmospheric lunar tide. The CSES EEJ data are also compared with lower thermospheric wind measurements by the Michelson Interferometer for Global High-Resolution Thermospheric Imaging (MIGHTI) onboard the Ionospheric Connection Explorer (ICON). The results suggest that the EEJ intensity correlates negatively with the equatorial eastward wind at 100–115 km, consistent with earlier studies. Contributions of different tidal wind components to longitudinal structures of the EEJ are evaluated. A four-peak structure during July–September can be largely explained by the eastward-propagating diurnal tide with zonal wavenumber 3 (DE3), while a two- or three-peak structure during December–January is mainly due to the combined effect of DE3 and the eastward-propagating diurnal tide with zonal wavenumber 2 (DE2). Furthermore, the CSES EEJ data are compared with the electron density measurements from the Langmuir probe onboard CSES. There is a positive correlation between the EEJ intensity and in-situ electron densities at ∼510 km from the same orbit, reflecting the plasma fountain effect. The correlation tends to be higher in the summer hemisphere, which may be due to the meridional wind in the thermosphere.

This brief report examines the ground-based total electron content (TEC) in Asian sector during August–October 2019, covering the period of a stratosphere sudden warming (SSW) occurred in Antarctica. The analysis reveals pronounced ionospheric day-to-day variability with distinct periodicities. The most dominant and long-lasting periodicities are quasi-10 days and quasi 14-day during September and October, while a quasi 6-day also present in September. The 10-day and 6-day TEC oscillations were attributed by previous studies solely to the Antarctic SSW while assuming negligible geomagnetic effects. By comparing co-located ground mesospheric wind observations, along with the interplanetary electric field (IEF) and geomagnetic activity (Kp index), we demonstrate that the quasi 14-day oscillation is mainly driven by low-level geomagnetic activities, while quasi-6 days oscillation is driven by mesospheric wind changes during the SSW. The 10-day oscillation, on the other hand, is driven by both IEF and mesospheric wind in September, but by IEF in October. These results demonstrate that low-level geomagnetic activities traditionally classified as “quiet conditions” can induce significant day-to-day oscillations in TEC, and their impacts should not be ignored when studying meteorological (e.g., SSWs) impacts on the ionosphere.

The mesospheric polar vortex (MPV) plays a critical role in coupling the atmosphere-ionosphere system, so its accurate simulation is imperative for robust predictions of the thermosphere and ionosphere. While the stratospheric polar vortex is widely understood and characterized, the mesospheric polar vortex is much less well-known and observed, a short-coming that must be addressed to improve predictability of the ionosphere. The winter MPV facilitates top-down coupling via the communication of high energy particle precipitation effects from the thermosphere down to the stratosphere, though the details of this mechanism are poorly understood. Coupling from the bottom-up involves gravity waves (GWs), planetary waves (PWs), and tidal interactions that are distinctly different and important during weak vs. strong vortex states, and yet remain poorly understood as well. Moreover, generation and modulation of GWs by the large wind shears at the vortex edge contribute to the generation of traveling atmospheric disturbances and traveling ionospheric disturbances. Unfortunately, representation of the MPV is generally not accurate in state-of-the-art general circulation models, even when compared to the limited observational data available. Models substantially underestimate eastward momentum at the top of the MPV, which limits the ability to predict upward effects in the thermosphere. The zonal wind bias responsible for this missing momentum in models has been attributed to deficiencies in the treatment of GWs and to an inaccurate representation of the high-latitude dynamics. In the coming decade, simulations of the MPV must be improved.