Charging regions, regions of charge, and storm structure in a partially inverted polarity supercell thunderstorm.

摘要

Dipoles, tripoles and other stacked charge arrangements are a temptingly convenient explanation of the electrical structure of entire storms and may have merit when storms can be considered a point phenomenon. However, the internal charge structure of storms with three-dimensional kinematic and microphysical structure (e.g., supercells) is not well-represented by single stack of pancake-shaped charge regions.In this study, lightning mapping and radar data from the 26 May 2004 supercell in central Oklahoma are used to examine successive arcs of lightning that developed in response to pulses in the storm's updraft. The evolution of lightning in updraft pulses was found to match with the established model of the formation and fallout of precipitation in supercells.Initial lightning in an arc was contained within precipitation lofted above the storm's weak echo region. Lower positive charge was centered at 7 km, negative charge at 10 km, and positive charge at 12 km, which is considered an elevated normal polarity tripole formed by the non-inductive charging collisions between ice crystals and riming graupel. Later and simultaneously, two different charge regions were associated with precipitation that reached the ground. To the left of the weak echo region, six charge regions were inferred to form a normal polarity arrangement, with positive charge carried on hail at the bottom of the stack. Further forward in the storm's precipitation region, four charge regions were inferred, with negative charge at the bottom of the stack, which is an inverted polarity structure. Flashes occasionally lowered positive charge to ground from this charge region. The charge structures in the precipitating region of the storm were due to charge advection from the elevated initial tripole formed in large inferred supercooled liquid water concentrations and additional non-inductive charging in lower supercooled water concentration about 5 km to the side of the storm's strongest updraft.The data suggest that the normal vs. inverted polarity nomenclature is applicable to neither the whole storm nor the charging process itself. Any given normal or inverted region may be significantly influenced by charging processes operating outside of it. It is recommended that future studies of charge structure in storms utilize an interpretive framework which distinguishes between charging regions and regions of charge and ties them to conventional supercellular structural features and their microphysical history as observed in radar fields.