Initial Electrification of Thunderstorms: Evidence for a Connection between Precipitation and Charging

摘要

The initial electrification stage of three thunderstorms has been analyzed in detail. In each case,the beginning of the initial electrification stage, as defined by the initial deflection of the electric field (E) at the surface, was coincident with the development of substantial reflectivity above the -5 o C level. Rapid growth of E (of at least 15 V m -1 s -1 ) at the surface started once large precipitation particles (reflectivity of at least 44 dBZ) reached above the -15 o C level, or when a substantial volume of large precipitation extended above -10 o C. In each case, the first lightning flash occurred within a few minutes of the onset of rapid E growth, and these flashes initiated at temperatures ranging from -10 to -21 o C. Positive and negative charge regions associated with the first flash were located between temperatures of -5 and -25 o C, and in one case, the only substantial charge regions present before the first flash were those involved in the flash. Our analyses suggest that initial electrification in each of these cases fits with charging via the non-inductive ice-ice collisional mechanism.