In this study, multiple data sets from Beidou geostationary orbit satellites total electron contents (TECs), ionosonde, meteor radar, magnetometer, and model simulations have been used to investigate the ionospheric responses in the Asian‐Australian sector during the September 2017 geomagnetic storm. It was found that long‐duration daytime TEC enhancements that lasted from 7 to 12 September 2017 were observed by the Beidou geostationary orbit satellite constellation. This is a unique event as the prominent TEC enhancements persisted during the storm recovery phase when geomagnetic activity became quiet. The Thermosphere‐Ionosphere Electrodynamics Global Circulation Model predicted that the TEC enhancements on 7–9 September were associated with the geomagnetic activity, but it showed significant electron density depletions on 10 and 11 September in contrast to the observed TEC enhancements. Our results suggested that the observed long‐duration TEC enhancements from 7 to 12 September are mainly associated with the interplay of ionospheric dynamics and electrodynamics. Nevertheless, the root causes for the observed TEC enhancements seen in the storm recovery phase are unknown and require further observations and model studies.

Statistical analyses were conducted to investigate the nighttime medium‐scale traveling ionospheric disturbances (MSTIDs) for the first time by using airglow images and Global Positioning System (GPS) data over central China during 2013–2015. Our results show that the phase fronts of perturbations are aligned from northwest to southeast direction and propagate toward the southwest direction. The characteristics of the nighttime MSTIDs observed by OI 630.0 nm images are consistent with those of the nighttime MSTIDs obtained from the GPS data. The phase velocity, period, wavelength, and amplitude of nighttime MSTIDs are 50–150 m/s, 0.5–1.5 h, 150–400 km, and 2%–15%, respectively, as measured from 630.0 nm images and GPS data. In addition, we utilized the simultaneous observations from OI 630.0 nm and OI 557.7 nm images to explore the relationship between nighttime MSTIDs and gravity waves (<100 km) in the mesopause. It is found that the nighttime MSTIDs frequently occurred in the summer solstice, which was not consistent with the occurrence of gravity wave observed in the mesopause. Our results indicate that the nighttime MSTIDs may be generated by the coupling of electrodynamic processes rather than be trigged by gravity waves from the lower atmosphere.

The difference in the hydrogen bonding interactions originating from different organic cations brings photoluminescence with distinct quantum yields.