A numerical study of negative sprites observed over two Florida storms

Abstract:

Although negative cloud-to-ground (CG) lightning strokes occur much more frequently than positive CGs, sprites caused by negative CGs are very rare. Past observations indicate that the ratio of negative and positive sprites is 1:200-300 [Barrington-Leigh et al., J. Geophys. Res, 106, 1741, 2001; Taylor et al., Geophys. Res. Lett., 35, L14812, 2008; Li et al., J. Geophys. Res., 117, A09310, 2012; Cummer et al., J. Geophys. Res., 118, 5176, 2013]. This has been recognized as one of the polarity asymmetry problems in lightning research [Williams, Plasma Sources Sci. Technol., 15 (2), S91, 2006]. On 12 September 2014, a few negative sprites were observed over two thunderstorms near the east coast of Florida. The sferic data indicate that the parent lightning strokes are all extremely impulsive, with the inferred impulse charge moment changes ranging from 650 to 1300 C km. In this talk, we present the simulation results of the response of the lower ionosphere to the quasi-electrostatic field of the parent lightning discharges of the negative sprites. The results indicate that the modifications of the ionosphere density by the parent CGs of the negative sprites vary significantly. The most impulsive lightning stoke may have increased the ionospheric density by nearly four orders of magnitude. Finally, we show that the sprite streamer initiation theory that mesospheric perturbations created by atmospheric gravity waves are the source of the inhomogeneities initiating sprite streamers [Liu et al., Nat. Commun. 6:7540, 2015] also works for the observed negative sprites.