An expanded view of the observations between April 13 and 15, 2022. (a) S ₄ index for all the 1.6 GHz GNSS signals transmitted by satellites with elevation greater than 25°. (b) Absolute vertical TEC derived from code and phase measurements provided by the platform and from the MIT Madrigal TEC maps. (c) Planetary K (Kp) index. (d) Disturbance Storm-Time (Dst) index. The yellow shade on the panels shows the region of enhanced TEC which coincides with a region of enhanced Kp and low Dst values.