Continuous variability in thunderstorm primary electrification and an evaluation of inverted-polarity terminology

Several field campaigns since the year 2000 have focused on anomalously electrified or “inverted polarity” thunderstorms. This study synthesizes these recent results, and considers how variability in the non-inductive relative-growth rate electrification mechanism might clarifying the meaning of “inverted polarity”. Instead of falling into two polarity classes, electrification and charge structure in strong updrafts vary continuously, as expected if depletion of supercooled water is a primary control on electrification. Two- or three-dimensional storm flows or other electrification mechanisms are required to combine one or more of these electrification regimes into “inverted” or otherwise complicated local charge sequences. Cloud flashes that result from these local charge sequences should be termed “positive” and “negative” instead of “normal” and “inverted” because cloud flashes of either polarity can occur at any altitude in thunderstorms.