Top panel: variations in mean upwards Doppler velocity (red diamonds) of vortex-related structures within the conspicuous vortex area (yellow circle in Figs. 1 and 4) and their respective errors (standard deviation, grey lines). Bottom panel: percentage of the conspicuous vortex area (yellow circle in previous figures) that is occupied by the identified upwards-moving vortex-related structures as a function of time, used for the derivation of the mean upwards Doppler velocity presented in the top panel.