In spite of the absence of convective updrafts, electrification in the decay stage of thunderstorms is dynamic. The electric field (E) at the ground beneath thunderstorms often exhibits an End Of Storm Oscillation during which E makes at least two polarity changes over a period of 30-75 minutes. As this presentation will show, substantial evolution in the vertical E profile and the vertical charge structure also occurs within the cloud during its decay. Four storms with surface E, radar, lightning mapping array, and in situ balloon E sounding data during the decay stage have been analyzed. These data support the idea that the main internal charge layers are carried on small ice particles and slowly descend. The uppermost charge region is likely a screening layer, the density and polarity of which change with time as successive internal charge regions fall out of the cloud and reach the ground. The same mechanism, the fall-out of the lowest charge regions, also can explain the oscillations of E at the ground during the decay stage.
展开▼
