Statistical analysis of solar activity variations of total electron content derived at Jet Propulsion Laboratory from GPS observations

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We analyzed the data series of the total electron content (TEC) derived at Jet Propulsion Laboratory from Global Positioning System (GPS) observations to investigate the solar activity effects of TEC on a global scale. The daily values of the solar extreme ultraviolet (EUV) fluxes in 0.1–50 nm wavelengths, 10.7 cm radio flux F10.7, and F10.7P (the average of daily F10.7 and its 81‐day mean F10.7A) are adopted to represent the solar EUV variability, respectively. The EUV fluxes are measured by the Solar EUV Monitor (SEM) spectrometer aboard Solar Heliospheric Observatory (SOHO). Three kinds of patterns (linearity, saturation, and amplification) can be detected in TEC versus F10.7P and EUV. A saturation feature exists in TEC versus F10.7 in the daytime, more pronounced at low latitudes than at middle and high latitudes. The saturation in the equatorial anomaly regions is strongest in equinoxes and weakest in the June solstice. In contrast, the amplification in TEC, as a novel feature, is mainly distributed in the northern middle, and high latitudes in the December solstice and in the Southern Hemisphere in the June solstice and the March equinox. It is the first time to determine where and when the linear, saturation, and amplification patterns are distributed in TEC. Further, the solar activity sensitivity of TEC is stronger at day than at night and more evident at lower latitudes than at higher latitudes. The solar activity dependent rates of TEC in the equatorial and low‐latitude regions have a minimum around the dip equator and maxima on both sides of the dip equator (near the crest of the equatorial anomaly). This structure is roughly aligned along the dip equator, being strongest in equinoxes and weakest in the June solstice, which highlights the importance of ionospheric dynamics related with E × B drift. In addition, this analysis confirms that in a statistical sense, a quadrate polynomial can well capture the long‐term solar activity dependency of TEC at specified local time.