Fig. 5From: Periodic oscillations of Doppler frequency excited by the traveling ionospheric disturbances associated with the Tonga eruption in 2022A map showing the geometry of GNSS TEC measurements for satellites GPS 31 (G−31), Beidou 4 (C−04), and Beidou 59 (C−59). The red circle shows the position of BULA station. The blue circle shows the conjugate point of the midpoint between Chofu–SarobetsuBack to article page