Dancing sprites: Detailed analysis of two case studies

Abstract

On 29–30 October 2013, a low‐light video camera installed at Pic du Midi (2877 m), recorded transient luminous events above a very active storm over the Mediterranean Sea. The minimum cloud top temperature reached −73°C, while its cloud to ground (CG) flash rate exceeded 30 fl min−1. Some sprite events have long duration and resemble to dancing sprites. We analyze in detail the temporal evolution and estimated location of two series of sprite sequences, as well as the cloud structure, the lightning activity, the electric field radiated in a broad range of low frequencies, and the current moment waveform of the lightning strokes. (i) In each series, successive sprite sequences reflect time and location of corresponding positive lightning strokes across the stratiform region. (ii) The longer time‐delayed (>20 ms) sprite elements correspond to the lower impulsive charge moment changes (iCMC) of the parent strokes (<200 C km), and they are shifted few tens of kilometers from their SP + CG stroke. However, both short and long time‐delayed sprite elements also occur after strokes that produce a large iCMC and that are followed by a continuing current. (iii) The long time‐delayed sprite elements during the continuing current correspond to surges in the current moment waveform. They occur sometimes at an altitude apparently lower than the previous short time‐delayed sprite elements, possibly because of changes in the local conductivity. (iv) The largest and brightest sprite elements produce significant current signatures, visible when their delay is not too short (~3–5 ms).

On the Series of +CG Lightning Strokes in Dancing Sprite Events

“…This is consistent with previous experience that SP+CGs often occur behind (but close to) the convective cores of the thunderstorm (Carey et al, ; Lang et al, ; Lu et al, ; Soula et al, ). This result is also consistent with other observations showing that sprites, including dancing sprite events, very often occur above the stratiform cloud area of the parent storm close to the region of secondary radar enhancement or bright band (Lang et al, ; Lyons, ; Soula et al, , , ; van der Velde et al, ; Yang et al, ). Without available radar data, the location of stratiform cloud region could be estimated in this study only roughly from satellite infrared cloud images (Figure ) and from the distribution of lightning activity (Figure ).…”

“…This short stroke interval, the spatial closeness of subsequent stroke, and the oriented fashion of the sequence suggest that these strokes are not independent from each other. Time intervals between SP+CG strokes in dancing sprite events are in the same range as time intervals between +CG strokes associated to lightning discharges with an extended network of discharge channels (Lang et al, ; Lu et al, ; Soula et al, , ). It is plausible to hypothesize that SP+CG strokes in many dancing sprite events are part of one long lightning discharge process.…”

“…The term “dancing” sprites (also called “jumping” sprites) was first suggested by Lyons () who observed several clusters of sprites flashing up one after the other above lightning discharges of length over 200 km in the USA. Since then, the term refers to a special type of sprite clusters in which the elements or subclusters appear in a sequence with lateral offset between the successive appearances (Bór, ; Füllekrug et al, ; Hardman et al, ; Lang et al, ; Lu et al, ; Lyons, ; Mlynarczyk et al, ; Soula et al, ; Williams et al, ; Winckler et al, ; Yang et al, ). Reports on these events agree in that dancing sprite sequences with total durations of several hundred milliseconds occur above the stratiform region of MCS and are often associated with extended lightning flashes spanning hundreds of kilometers that can include sequences of several +CG lightning strokes (Lang et al, ; Soula et al, ; Walter Lyons, personal communication, 2017).…”

“…Dancing sprites with short delayed ( dt ≤ 20 ms) and long delayed ( dt > 20 ms) elements have been associated to parent lightning flashes that include several SP+CG lightning strokes (Füllekrug et al, 2013b; Hardman et al, ; Soula et al, ; Winckler et al, ) or to single stroke lightning discharges with CC and superimposed current surges (Lu et al, ; Yang et al, ). The important role of in‐cloud extension and progression of lightning leaders in the production of sprites delayed and displaced with respect to their parent lightning stroke has been emphasized (Lu et al, ; Soula et al, ). This finding is coherent with the observation that elements of a dancing sprite cluster appear often more or less aligned (Bór, ).…”

Gigantic jet discharges evolve stepwise through the middle atmosphere

“…The current density at 30 km altitude where the channel diameter was 550 m is 3.5 × 10 −3 A m −2 . The re-activation of beads and new patches in the upper jet could be a result of the enhancement of electric fields in the mesosphere as result of large vertical charge transfers, like in the case of sprites 40,41 . The total charge moment change by the end of the TJ stage is 2300 C km.…”