Global long-term trends in the total electron content

Total electron content (TEC) is an important parameter for ionospheric dynamics, global navigation satellite system/Global Positioning System (GNSS/GPS) signal propagation and related applications of GNSS/GPS signals. Despite this fact, the long-term trends in TEC have been studied only a little. Here, we analyze the JPL-35 (Jet Propulsion Laboratory-35) homogeneous series of global TEC data for 1994-2014 for selection of the optimum solar activity proxy for TEC analyses and the UPC (Universitat Polit & egrave;cnica de Catalunya) TEC data over 2003-2023 for estimating long-term trends in TEC. TEC trends are predominantly negative. TEC trends reveal a clear wavenumber 2 longitudinal structure in low/equatorial latitudes with strong negative trends in belts 0-60 and 180-240 degrees E and weak trends in 90-150 and 270-330 degrees E. For more detailed information on TEC trends, a longer series of reliable TEC data is required.