Resolution of the sprite polarity paradox: The role of halos

Abstract

[1] This study revisits the sprite polarity paradox, first manifest by observations that exceptional cloud-to-ground flashes with negative polarity generally did not produce detectable sprites. The paradox is here resolved by the Transient Luminous Event (TLE) known as the halo, which on account of its inferior brightness (0.3 MR versus 1.5 MR) and substantially shorter duration (1 ms versus 10-100 ms) in comparison with the sprite, is not readily detectable in ground-based video cameras with standard field duration (16.7-20 ms). Observations with improved temporal resolution (ISUAL (Imager of Sprites and Upper Atmospheric Lightnings) from space and PIPER (Photometric Imager of Precipitated Electron Radiation) observations from the ground) provide evidence that flashes with negative polarity dominate the global halo population, and that the halo numbers are more than sufficient to account for the previously missing TLEs. The evidence for lightning polarity-dependent TLEs (sprites, positive and halos, negative) is attributable to the well established but incompletely understood contrast in the behavior of negative and positive lightning flashes to ground.

Lightning and middle atmospheric discharges in the atmosphere

“…Rare observations of sprites associated with À CG discharges seem to contradict the proposed Wilson's hypothesis of initiations of sprites based on electric field calculations, however, the observation of halos by ISUAL payload and ground based PIPER system show abundance of halos associated with ÀCG discharges (Frey et al, 2007;Williams et al, 2012). Using ground based Table 2 Summary of emissions from sprites (after: Liu et al, 2006;Pasko, 2007).…”

“…Because of smaller SIR associated with À CG discharges, streamer formation/development is hindered and hence sprite structure is rarely observed in association with À CG discharges, but halos are observed. Recent observations with improved temporal and intensity resolutions (Newsome and Inan, 2010;Williams et al, 2012) and modeling studies (Asano et al, 2008(Asano et al, , 2009) indicated that both þCG and À CG discharges are equally capable of triggering discharges in the mesosphere (sprites and halos). However, streamer evolution/development strongly depends on electric field and local electron density profile (Qin et al, 2011(Qin et al, , 2012a(Qin et al, , 2012b.…”

“…They are produced by both þCG and À CG discharges (Frey et al, 2007;Williams et al, 2012). Halos are much dimmer than sprites (Kuo et al, 2008;Takahashi et al, 2010).…”

“…The brightness and duration of halos depend on peak current and polarity of discharges (Fig. 11) (Williams et al, 2012). Halos associated with þCG flashes are brighter and last for longer duration.…”

“…Observations with improved temporal and intensity resolutions from the Imagers of Sprites and Upper Atmospheric Lightnings (ISUAL) payload on FORMOSAT-2 satellite provide evidence that flashes with negative polarity dominate the global halos population (Williams et al, 2012). Further, from the analysis of ISUAL data, Chen et al (2008) showed that global average rates of elves and sprites are in the ratio of roughly 9:1; and that elves and halos occur over sea surface and costal area at almost twice their over land rates.…”