Fig. 1

Times series of vertical TEC during Tonga volcanic eruption on 15 January 2022. (Left) The colored line and blue triangle indicate the trajectory of the ionospheric pierce point (IPP) during 4–9 UT and the location of GNSS station. The IPP are calculated assuming an ionospheric shell height of 300 km. The filled black and white circles on the trajectories indicate the beginning and end of the IPP location. The red star denotes the location of Tonga (184.6°E, 20.5°S). (Right) The variations of vertical TEC measured from six stations near Tonga for PRN#10(red), PRN#23(blue), and PRN#32(green). The black vertical dashed lines indicate the time of the 2022 Tonga volcanic eruption