The study uses data from soundings of the SABER satellite to examine the mesospheric inversion layer (MIL) and the related gravity wave energy and instability. In the mesosphere and lower-thermosphere (MLT) region, upper inversions occur with less than 40 % frequency, while the lower inversions are below 20 %. High gravity wave energy (~100 J/kg) in the upper MLT (85–90 km) is linked to instability, driving inversion phenomena. Conversely, the trend is less pronounced in the lower-MLT region.

This study, for the first time, convincingly attests to the two-step geospace storm being the best possible solar–terrestrial event of opportunity for realizing a technique for estimating the interplanetary magnetic field (IMF) B_z component threshold for the formation of the substorm current wedge. The data from INTERMAGNET magnetometer network on the two-step geospace 23–24 April 2023 storm yield the IMF B_z threshold for the formation of the substorm current wedge of –(22–30) nT.

Our research examines solar wind interactions with magnetic structures from the Sun. Observations at different longitudes near the ecliptic plane show the progression of interactions between a co-rotating interaction region and a magnetic-cloud-like structure. These interactions cause significant changes, including compression and wave formation, enhancing our understanding of the complex nature of solar wind impacting Earth's magnetic environment.

The amplitude of subionospheric very low-frequency (VLF) radio signals does not show a symmetrical behavior over the year, which would be expected from its dependency on the solar position. The VLF amplitude rather shows a distinctive sharp decrease around October, which is hence called the "October effect". This study is the first to systematically investigate this October effect, which shows a clear latitudinal dependency.

Total electron content (TEC) affects the GPS (Global Positioning System) signal propagation and applications of GPS signals like positioning. Here, we study long-term trends in TEC. TEC trends are regionally different and predominantly negative; all statistically significant trends are negative. TEC trends reveal a clear wavenumber 2 longitudinal structure in low/equatorial latitudes, with strong negative trends in belts 0–60° E and 180–240° E and weak trends in belts 90–150° E and 270–330° E.

This study analyzes changes in the ionospheric response to solar flux over five complete solar cycles (1957 to 2023). We use Juliusruh hourly data of the peak electron density of the F2 layer, NmF2, and three solar extreme ultraviolet (EUV) radiation proxies. The response is better represented by a cubic regression, and F30 shows the highest correlation for describing NmF2 dependence over time. These results reveal a decrease in NmF2 influenced by the intensity of the solar activity index.

This study explores how solar sunspot number (Sn) compares with other solar indicators like solar radio fluxes in predicting changes in Earth's ionosphere, particularly its critical frequency, over more than 60 years. The work finds that Sn, despite recent fluctuations in other proxies, remains the most stable predictor across all time periods. When adjusting for potential data saturation, Sn outperforms other proxies, providing a more accurate forecast of long-term ionospheric trends.

The EISCAT_3D radar is a new ionospheric radar under construction in the Fennoscandia region. The radar will make measurements of plasma characteristics at altitudes above approximately 60 km. The capability of the system to make these measurements at spatial scales of less than 100 m using multiple digitised signals from each of the radar antenna panels is highlighted. There are many ionospheric small-scale processes that will be further resolved using the techniques discussed here.