Total Lightning Characteristics and Inferred Charge Structure of Ordinary Convection

With the advent of continuously operational three-dimensional (3-D) lightning mapping systems, complete observations of a thunderstorm's electrical development (e.g., total flash characteristics and inferred main charge regions) are now routinely available. Recent studies examining correlations between 3-D lightning flash characteristics and convective intensity have shown promising results; however, recent emphasis has been placed primarily on complex modes of convection (e.g., supercells and squall lines) with often only a limited portion of the cell's lifetime examined. Although it is the most ubiquitous and basic cell type, ordinary, single-cell convection has received relatively little recent attention in the lightning community. Observing the three-dimensional flash characteristics of a large sample of ordinary, isolated convective cells on a cell-by-cell basis could provide insight into statistically significant correlations between radar inferred convective intensity and total lightning without the complexities often associated with supercell or multi-cell convection. Given their structural simplicity, it should also be possible to examine details of the vertical structure of lightning and inferred charge of these isolated cells.

Toward these objectives, we examined several isolated, non-severe, warm season thunderstorms (ordinary thunderstorms) within range of Vaisala Inc.'s Dallas-Fort Worth (DFW) Lightning Detection and Ranging (LDAR II) network. The kinematic and microphysical properties of each convective cell were inferred from level II DFW Weather Surveillance Radar 1988 Doppler (WSR-88D) data. Various radar parameters that are indicative of convective intensity (e.g., vertically integrated liquid (VIL) and 30 dBZ echo top) were compared against the cell total and vertical profile of flash density (flashes min-1km-1), flash origin density, and flash source density for several ordinary thunderstorm cases during their entire lifecycle.

Preliminary results suggest that flash origins favor a bimodal distribution as observed in prior studies. The peak concentration of observed intracloud (IC) flash origins were located around the 10km level (i.e., T ≈ -40ºC, or the upper layer in bimodal distribution cases) throughout the lifetime of the cell as in past studies. In addition, IC flashes extended primarily above the -10ºC isotherm suggesting a net positive charge in this region. Further analysis and interpretation of lightning flash characteristics, comparison with radar measured kinematic and microphysical properties, along with implications of these preliminary results for our basic understanding of cloud electrification and for short-term operational forecasting, will be presented.