The total electron content (TEC), GNSS/GPS signal propagation and applications of GNSS/GPS signals like positioning. Here we study long-term trends in TEC. TEC trends are regionally different; they are found to be very 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 90–150° E and 270–330° E.

Increasing concentration of greenhouse gases, particularly of CO₂, in the atmosphere causes well-known heating of the troposphere and surface. However, the increasing concentration of CO₂ also affects higher levels of the atmosphere, the stratosphere, mesosphere, thermosphere, and ionosphere, where it results in remarkable long-term trends. This article reviews significant progress in investigations of long-term trends in the mesosphere, thermosphere, and ionosphere during the period 2018–2022.

This paper is devoted to the occurrence of discontinuities in the ozone concentration data from the selected reanalyses, because they have large impact to the results of trend studies. The discontinuity occurrence is reanalyse dependant. The discontinuities frequently occur at the middle stratosphere and in the troposphere for a certain reanalyses. According our opinion, the reanalyses data can be used in trend studies especially in the lower stratosphere.

This paper investigates a feature in the Southern Hemisphere ionosphere that is observed near midday in the form of a localized enhancement of the electron density. After being discovered in global ionospheric maps, the enhancements were also observed via in situ measurements of the electron concentration. The probability of detecting an enhancement is maximal during the autumn–winter period and does not seem to be directly dependent on geomagnetic indices or solar wind parameters.

The relation between the occurrence of ionospheric irregularities and the spatial gradient of TEC derived from two closely located stations, located within the equatorial region over Ethiopia, was investigated. The relationship between σ(∆TEC/∆long) and ROTI_ave correlate linearly with correlation coefficients of C = 0.7975 and C = 0.7915 over ASAB and DEBK, respectively. In addition to latitudinal gradients, the longitudinal gradient of TEC has a significant contribution to the TEC fluctuations.