An analysis of five negative sprite‐parent discharges and their associated thunderstorm charge structures

Abstract

In this study we analyze the discharge morphologies of five confirmed negative sprite‐parent discharges and the associated charge structures of the thunderstorms that produced them. The negative sprite‐parent lightning took place in two thunderstorms that were associated with a tropical disturbance in east central and south Florida. The first thunderstorm, which moved onshore in east central Florida, produced four of the five negative sprite‐parent discharges within a period of 17 min, as it made landfall from the Atlantic Ocean. These negative sprite‐parents were composed of bolt‐from‐the‐blue (BFB), hybrid intracloud‐negative cloud‐to‐ground (IC‐NCG), and multicell IC‐NCGs discharges. The second thunderstorm, which occurred inland over south Florida, produced a negative sprite‐parent that was a probable hybrid IC‐NCG discharge and two negative gigantic jets (GJs). Weakened upper positive charge with very large midlevel negative charge was inferred for both convective cells that initiated the negative‐sprite‐parent discharges. Our study suggests tall, intense convective systems with high wind shear at the middle to upper regions of the cloud accompanied by low cloud‐to‐ground (CG) flash rates promote these charge structures. The excess amount of midlevel negative charge results in these CG discharges transferring much more charge to ground than typical negative CG discharges. We find that BFB discharges prefer an asymmetrical charge structure that brings the negative leader exiting the upper positive charge region closer to the lateral positive screening charge layer. This may be the main factor in determining whether a negative leader exiting the upper positive region of the thundercloud forms a BFB or GJ.

Analysis of lightning strokes associated with sprites observed by ISUAL in the vicinity of North America

“…Figure 8 shows the histogram of peak currents for these sprites, including 38 negative strokes and 209 positive strokes. Generally speaking, the negative CG strokes associated with ISUAL sprites tend to have higher peak current (with mean and median of -195 and -185 kA, respectively) than positive strokes (with mean and median of +115 and +97 kA, respectively), which is consistent with the findings from ground-based observations (e.g., Li et al 2012;Lu et al 2013;Boggs et al 2016). For eight negative sprite-producing strokes over oceans, the mean peak current is -169 kA, considerably smaller than that (-202 kA) for the 30 negative strokes over ocean.…”

“…This validates our previous work that selected negative CG strokes with peak current in excess of -80 kA as the candidate sprite producers ). The minimum peak current associated with negative sprites reported in the literature was -93 kA (Barrington-Leigh et al 1999;Li et al 2012;Boggs et al 2016), and the mean value is -153 kA (compared to -195 kA in our analysis). Therefore, although the peak current is not an ideal proxy to determine the potential for a specific stroke to produce mesospheric breakdown, it can be at least used as an initial criterion to sort out the negative strokes with higher chance to produce sprites.…”

“…Figure 7a shows the histogram of iCMCs for positive and negative CG strokes associated with ISUAL sprites, showing a log-normal distribution (which is especially clear for positive sprites). The mean and median iCMC of positive causative strokes for 326 sprites observed by ISUAL is +346 and +280 C km, respectively; in contrast, the mean and medium iCMCs associated with 69 ISUAL-registered negative sprites are -709 and -649 C km, respectively, which are not significantly different from the average iCMC (-739 C km) for a total of eleven negative sprites examined by Li et al (2012) and Boggs et al (2016). Therefore, the threshold for negative sprites is substantially higher (by a factor of ~2) than that for positive sprites, which is consistent with the idea that the threshold for propagation of negative streamers is much higher than that for positive streamers (e.g., Qin et al 2011).…”

“…Therefore, although the peak current is not an ideal proxy to determine the potential for a specific stroke to produce mesospheric breakdown, it can be at least used as an initial criterion to sort out the negative strokes with higher chance to produce sprites. For negative CG strokes, the sprite production is predominantly produced through the impulse charge transfer within several milliseconds after the return stroke (Li et al 2012;Boggs et al 2016;Lu et al 2016), and the contribution of long continuing current (if present) is usually negligible.…”

Sprite possibly produced by two distinct positive cloud-to-ground lightning flashes

“…Up to now, the TLE family includes sprites (Sentman et al 1995;Lyons 1996;Winckler et al 1996;Cummer et al 2006;Yang et al 2008;Savtchenko et al 2009;Lang et al 2010;Suzuki et al 2011;Boggs et al 2016;Peng et al 2017), elves (Emissions of Light and VLF perturbation due to EMP Sources) Barrington-Leigh et al 2001;Kuo et al 2007;Wu et al 2017), halos ), blue starters, blue jets and gigantic jets (Pasko 2003;Su et al 2003;Kuo et al 2009;Chou et al 2011;Yang and Feng 2012;Liu et al 2015b). Sprites are usually produced by intense lightning discharges and are observed between about 40 -90 km altitude above thunderstorms (Sentman et al 1995;Hardman et al 2000;Neubert et al 2001;Su et al 2002;Pinto et al 2004;Cummer et al 2006; Van der Velde et al 2006;Yang et al 2008Yang et al , 2013aYang et al , 2015Lu et al 2017).…”