Microphysics and Positive Lightning in Hokuriku Winter Clouds
The microphysics of the frequent, and frequently positive, lightning of Hokuriku winter clouds was investigated by systematic, in situ observation of individual precipitation particle type and charge.
SOURCE: Journal of Geophysical Research: Atmospheres
Model of cloud development, charge evolution, and cloud-to-ground lightning initiation in Hokuriku winter clouds. The main charging mechanism is riming electrification, in which collisions between graupel particles and ice crystals leave them oppositely charged, with the polarity of the separated charge dependent on temperature. Mid-level, negatively charged graupel particles in the mature stage are the main source of negative lightning. Positively charged ice crystals, blown out of the upper level of mature stage clouds by wind shear and then descending, may be the main source of positive lightning. Credit: Takahashi et al. , Figure 10
The winter storm clouds of the Hokuriku region of Japan, though relatively shallow, are famous not only for producing prodigious amounts of snow, but also for producing high frequencies of lightning. An unusually high proportion is positive lightning, that is, lightning that has an electric charge opposite of the more common negative lightning.
Takahashi et al.  present a comprehensive and detailed analysis of balloon-borne and ground-based observations of these storms, attributing microphysical parameters in the thunderclouds to lightning types and origins. The authors found that the space charge increases with the number concentrations of graupel particles and ice crystals, indicating riming electrification. The charge structures of the different stages of the cloud life cycle were also obtained.
In addition, they found enormous numbers of small ice particles which appear to have been ejected from the graupel particle surface in inter-particle collisions. The small particles generated by this new ice multiplication mechanism could contribute substantially to seeding the development of the large numbers of ice crystals which support the high electrification of these clouds.
The results of this manuscript shed substantial light on the relationship between the distribution of hydrometeor particles and charge structure.
Citation: Takahashi, T., Sugimoto, S., Kawano, T., & Suzuki, K. . Microphysical structure and lightning initiation in Hokuriku winter clouds. Journal of Geophysical Research: Atmospheres, 124. https://doi.org/10.1029/2018JD030227
—Minghua Zhang, Editor in Chief, JGR: Atmospheres
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