Global long-term trends in the total electron content

The total electron content (TEC) is an important parameter for the ionospheric dynamics, GNSS/GPS signal propagation and related applications of GNSS/GPS signals. Despite this fact the long-term trends in TEC have been studied a little only. Here we analyze the homogeneous series JPL-35 of global TEC data for 1994–2014 for selection of the optimum solar activity proxy for TEC analyses, and the UPC TEC data over 2003–2023 for estimating long-term trends in TEC. TEC trends are very predominantly 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. For more detailed information on TEC trends a longer series of reliable TEC data is required.