Fig. 4From: Lightning evolution and VLF perturbations associated with category 5 TC Yasa in the South Pacific Regiona–p NPM signal amplitude (red) during 10 to 25 December 2020 which includes TC Yasa days. The mean signal amplitude for five quiet days (black) along with the ± 2σ (green) and ± 3σ (cyan) are shown. The NPM signal phase on 11 December is shown in purple. Signal amplitude perturbations are marked with blue horizontal arrowsBack to article page