Cloud-to-ground lightning: climatological characteristics and relationships to model fields, radar observations, and severe local storms

Abstract

Data for nearly 2 million lightning flashes recorded during the 1985-86 warm seasons were evaluated to determine some of the climatological characteristics of cloud-to-ground lightning. Among the characteristics studied were the seasonal, diurnal, and spatial variations of positive and negative lightning strike activity, including flash rates, signal strength, and flash multiplicity. The lightning data were also compared to manually digitized radar data, reports of tornadoes, large hail, and damaging winds, and to analyzed 0000 UTC fields obtained from operational numerical models. The diurnal distribution of lightning revealed that peak rates occurred later than in other sections of the country, reflecting the prevalence of nocturnal convection within much of the NSSL network. An analysis of the spatial variations in lightning activity also confirmed the existence of distinct climatological regimes within the network. A good correspondence between lightning frequency and radar echo intensity was found. Both positive and negative flashes were found to be strongly correlated with the low-level moisture flux and circulation, as characterized by favourable moisture convergence, cyclonic relative vorticity, and strong upward vertical motions in the boundary layer. Contrary to expectations, freezing level height and wind shear were not nearly as important as the boundary layer fields. -from Authors