Detection of daytime sprites via a unique sprite ELF signature

Abstract

Abstract. On August 14, 1998, 3 separate daytime sprite events were detected via a unique extremely low frequency (ELF) sprite signature. The onset of the sprite ELF signatures was delayed by 11.0-13.2 ms from positive cloudto-ground strokes which had attained exceptionally large charge moment (charge times height) changes of 3900-6100 C-km. It is shown that a charge moment change of 6100 C.km may have been sufficient for conventional breakdown at _•54 km altitude, assuming an experimentally measured ion conductivity profile of Holzworth et al., [1985].The daytime sprites themselves contained unusually large charge moment changes of _•2800 C.km, ___1200 C.km, and m910 C-km. IntroductionSprites are luminous discharges which photometrically have only been documented at night in part because of the dominance of Rayleigh scattering of sunlight during the day. were correlated with bright sprites on video but were temporally distinct from +CG slow tails. These slow field changes were unique in that they were not immediately preceded by the very low frequency (VLF) radiation produced by a In this paper, we report the first detection of daytime sprite events via their ELF "fingerprint". It will be shown that the value of the parent discharge charge moments at the onset of the daytime sprite ELF signatures is much greater than for the onset of nighttime sprite ELF signatures. InstrumentationThe GPS-based NMT radio atmospheric (sferic) system was used to acquire very broadband (<1 Hz-250 kHz) electric field data. Pre-and post-trigger data of a combined fixed length was stored at a 500 kHz sample rate whenever a bipolar threshold was exceeded. The system was able to immediately rearm after the post-trigger was stored. This feature, combined with a high data bandwidth, translated into a 100% detection efficiency for all sferics which met the sensitive trigger criteria. This resulted in an unambiguous identification of CG occurrence, making it possible to discriminate between slow tails which are associated with CGs and delayed slow field changes associated with sprites. The preand post-trigger lengths were configurable, but were set to 2 and 6 ms respectively on August 14, 1998. The electric field data was also stored continuously at a 10 kHz sample rate.The NMT sferic system was located on a mountain ridge at Langmuir Laboratory, NM. In order to determine the electric field intensification due to the ridge, sferics at >800 km range were compared between the NMT sferic system and an electric field sferic system located ___30 km away on level terrain. This comparison revealed that the ridge intensified the electric field by a factor of 1.9+0.2. The NMT system's electric field values were converted to fiat terrain values and these were used for the ELF propagation model. Analysis methodThe lightning current moment (current times vertical channel length) was extracted quantitatively by a tech- 871

Underlying mechanisms of transient luminous events: a review

“…This contradicts with observations since the measured lightning charge moment changes in TGF-associated strokes are 50-500 times smaller than what the runaway theory predicts (Cummer et al, 2005). However, it is still possible that some TGFs are generated by enormous lightning discharges with charge moment changes of several thousands of C km (Stanley et al, 2000;Cummer and Füllekrug, 2001).…”

“…Neubert et al, 2008;Pasco, 2010;Raizer et al, 2010). The polarity asymmetry of sprite-producing lightning (Boccippio et al, 1995;Lyons, 2006;Williams et al, 2007), as well as the fact that the charge moment change of the causative +CG must be greater than ∼500 C km to produce sprites (Stanley et al, 2000;, is far from being well understood.…”

“…Boccippio et al, 1995;Williams et al, 2007). The sprites and mesospheric TLEs occur infrequently since the charge moment change of the causative +CG must be more than a value of the order of 500 C km in order to initiate the sprite discharge (Stanley et al, 2000;Hiraki and Fukunishi, 2006). The point of sprite initiation occurs in the 60-80 km altitude range, while the brightest region of the sprite body is usually observed in the altitude range 65-85 km (Neubert et al, 2008).…”

Lightning-associated VLF perturbations observed at low latitude: Occurrence and scattering characteristics

“…Also it has been estimated that an unusually large charge moment change of about 8000 C-km is required to initiate a daytime sprite at a 50-km altitude (Fernsler and Rowland, 1996). Stanley et al (2000) detected 3 separate daytime sprites on 14 August, 1998, via a unique sprite ELF signature recorded at a site in New Mexico, following exceptionally large lightning discharges. Farges et al (2005) were the rst to measure infrasound waves emitted from sprites past sunrise and onwards into the daytime, and suggested the occurrence of daytime sprites.…”

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

“…As shown in Fig. 2a, the sferic signal for the positive sprite also contains a second slow pulse that could be unambiguously identified due to the lack of higher frequency (> 1 kHz) radiation (e.g., Stanley et al 2000;Füllekrug et al 2001;Hu et al 2002;Lu et al 2013), which is attributed to the current flow along sprite bodies (Cummer et al 1998;Pasko et al 1998). By examining sprite-associated sferics with distinct sprite current signal, we found that a discernible sprite current signal, not surprisingly, are unique to those sprites that appeared bright (with a relatively large vertical scale).…”