A semicontinuous current flow has been measured above electrified clouds. Called the Wilson current, this phenomenon has long been considered a critical component of the global electric circuit; however, only a few studies have directly investigated this current, yielding only a few dozen measurements.
Reporting in the Journal of Geophysical Research-Atmospheres, Mach et al. greatly expanded on this sparse collection of measurements. Using conductivity and electric field sensors mounted on high-altitude aircraft, they determined current densities along 850 overflights of electrified clouds.
Using these data, which represent more than a decade of observations of land-based and oceanic storms, the authors estimate the Wilson current for each of the clouds overflown. They find that one third of the clouds studied did not have lightning yet still generated significant Wilson currents, confirming that such "shower" clouds do play a critical role in the global electric circuit.
They also find that 7 percent of storms produced current flows that were opposite in polarity from the typical thunderstorms, diminishing the contribution storms make to the global electric circuit.
The results of this paper will contribute to a better understanding of the global electric circuit.
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