(a) Daily average of the VTEC derived from the tomography method at 9.3 and 21.0 LT. The average was computed based on data between 40° S and 40° N latitude. METOP data was missing to perform reconstructions at DOY 79/2013. (b) VTEC percentage relative to the first day of the time series, considered here as a quiet day (low Kp values). The dashed lines indicate the day of the storm onset. The VTEC unit is given in TECU.