Comparisons of total currents based on storm location, polarity, and flash rates derived from high‐altitude aircraft overflights

Abstract

We determined total conduction (Wilson) currents and flash rates for 850 overflights of electrified clouds spanning regions including the southeastern United States, the western Atlantic Ocean, the Gulf of Mexico, Central America and adjacent oceans, central Brazil, and the South Pacific. The overflights included storms over land and ocean, with and without lightning, and with positive (i.e., upward directed) and negative Wilson currents. The mean current for oceanic storms with lightning was 1.6 A whereas the mean current for land storms with lightning was 1.0 A. The mean current for oceanic storms without lightning was 0.39 A, and the mean current for land storms without lightning was 0.13 A. On average, land storms with or without lightning had about half the mean current as their corresponding oceanic storm counterparts, while ocean (land) storms with lightning produced 4.1 (7.7) times the mean current as storms without lightning. About 78% of the land storms had detectable lightning, while only 43% of the oceanic storms did. When only lightning storms are considered, land storms had 2.8 times the mean flash rate as oceanic storms (2.2 versus 0.8 flashes min−1, respectively). Approximately 7% (56) of the overflights had negative (or downward directed) Wilson currents. The mean and median total Wilson currents for negative polarity storms were −0.30 and −0.26 A whereas the mean and median currents for positive polarity storms were 1.0 and 0.35 A. We found no significant regional‐ or latitudinal‐based patterns in our total Wilson currents. At 20 km altitude, the full width at half maximum in the electric field profile varied between 12 and 16 km. At 15 km altitude, the full width at half maximum in the electric field profile varied between 1.7 and 3.5 km. Our results indicate that simple scaling laws between cloud top height and lightning flash rates or total storm current output may not be universally applicable. Our results also indicate that some clouds without lightning also contribute to the global electric circuit.