Transient luminous events above two mesoscale convective systems: Charge moment change analysis

Charge moment change (Delta M-Q) data were examined for 41 positive cloud-to-ground (+CG) lightning discharges that were parents of transient luminous events (TLEs; mainly sprites) over two different storms: 9 May (20 parents) and 20 June 2007 (21). Data were broken down by contributions from the impulse Delta M-Q (i Delta M-Q), within the first 2 ms of the return stroke, and the Delta M-Q from the continuing current (CC), which can last tens of ms afterward. Three-dimensional lightning mapping data provided positions for the in-cloud components of the parent +CGs. Charge and charge density neutralized by the strokes were estimated. The 20 June parents were more impulsive than 9 May, with increased i Delta M-Q and CC amplitude but reduced CC duration. Total Delta M-Q values between the two storms were very similar, averaging similar to 1800 C km. Estimated charge density on 20 June was nearly twice that on 9 May, consistent with the 20 June storm being more intense with a stronger electrical generator. Lightning metrics were analyzed for 9 high-i Delta M-Q (>300 C km) +CGs that did not produce an observable TLE on 20 June, and compared to that day's TLE parents. Non-TLE +CGs had reduced CC magnitudes and duration, with less total Delta M-Q. Photogrammetric estimates of TLE azimuthal swaths were positively correlated with similar metrics of the in-cloud portions of the parent +CGs, as well with total Delta M-Q. The implications of all these results for the Delta M-Q theory of sprite initiation, and for the relationship between sprite development and in-cloud discharging, are discussed.