Wednesday, 23 January 2008
Behavior of lightning and updrafts for severe and non-severe storms in northern Alabama
Exhibit Hall B (Ernest N. Morial Convention Center)
Numerous case studies and recent modeling studies have found that various metrics of updraft intensity appear to be reasonably well correlated to lightning production in thunderstorms, particularly severe thunderstorms. Indeed, the relationship between updraft and lightning flash rate is hypothesized to be the physical connection between a lightning “jump” signature and manifestations of severe weather such as tornadic activity. This study further examines this connection using a combination of dual-Doppler wind retrievals made with the UAH ARMOR dual-polarimetric and KHTX WSR-88D Doppler radar pair, together with northern Alabama Lightning Mapping Array (LMA) data. The dual-Doppler data were used to construct three-dimensional wind fields for a number of severe and non-severe storms and the retrieved vertical velocity fields were subsequently compared to collocated total lightning flash rates observed by the LMA. Particular attention was paid to the timing of updraft pulses relative to changes in the flash rate, with the goal of assessing impacts on warning decision lead time.
Preliminary results from the analysis of at least one strong (but non-severe) Alabama thunderstorm case suggests that the temporal correlation between updraft strength and lightning flash rate can be “blurred” via evolution of the precipitation ice core aloft which forms within the updraft, but drives the strongest charge separation via its relative descent back through ascending smaller ice crystals in the updraft. Hence, a several minute lag was observed between the most intense and deepest extent of the updraft pulse and the peak in lightning flash production (a manifestation of the “jump signature” and an important physical consideration in considering lightning-trend related nowcast lead times). We will present similar results for several other case types, both severe and non-severe, to examine the degree of systematic behavior in lightning and updrafts across a spectrum of storm types.