In :from IPython.display import Image
Collisions of ice crystals and graupel in the presence of supercooled water are the primary mechanism of thunderstorm electrification.
After microscale electrification, sedimentation of charged, precipitation-sized hydrometeors results in net charge regions.
This is sufficient to explain the three main charge regions observed in the "normal tripole."
In :Image('Electrification-to-charge-structure.png', width="40%")
Bruning et al. 2014 - Anomalous electrification (paywall) http://dx.doi.org/10.1016/j.atmosres.2012.10.009
Depletion rate of supercooled liquid water content controls length of time spent in positive charging region.
Suggests we should observe a continuous shift of position of lower positive charge through a range of altitudes depending on the depletion rate.
Depletion rate might be controlled by:
Storms on the high plains of the US tend toward these low-depletion-rate conditions.
In :Image('Bruning2014-Fig3.png', width="60%")
Bruning et al. 2010 - Formation of charge structures in a supercell http://journals.ametsoc.org/doi/pdf/10.1175/2010MWR3160.1 (PDF)
Illustrates storm-relative (Fig. 1, Fig. 8) organization of thunderstorm charge into different net structures.
Explanation of these complicated charge structures
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