Analysis of thunderstorm and lightning activity associated with sprites observed during the EuroSprite campaigns: Two case studies

Serge Soula,Oscar Van Der Velde,Joan Montanyà,Torsten Neubert,Olivier Chanrion,Michal Ganot

doi:10.1016/j.atmosres.2008.06.017

Abstract

During the summers of 2003 to 2006 sprites were observed over thunderstorms in France by cameras on mountain tops in Southern France. The observations were part of a larger coordinated effort, the EuroSprite campaigns, with data collected simultaneously from other sources including the French radar network for precipitation structure, Meteosat with images of cloud top temperature and the Météorage network for detection of cloud-to-ground (CG) flash activity. In this paper two storms are analyzed, each producing 27 sprite events. Both storms were identified as Mesoscale Convective Systems (MCS) with a trailing stratiform configuration (ST) and reaching a maximum cloud area of ~ 120,000 km 2. Most of the sprites were produced while the stratiform area was clearly developed and during periods of substantial increase of rainfall in regions with radar reflectivity between 30 and 40 dBZ. The sprite-producing periods followed a maximum in the CG lightning activity and were characterized by a low CG flash rate with a high proportion of + CG flashes, typically around 50%. All sprites were associated with + CGs except one which was observed after a − CG as detected by the Météorage network. This − CG was estimated to have − 800 C km charge moment change. The peak current of sprite-producing + CG (SP + CG) flashes was twice the average value of + CGs and close to 60 kA with little variation between the periods of sprite activity. The SP + CG flashes were further characterized by short time intervals before a subsequent CG flash (median value < 0.5 s) and with clusters of several CG flashes which suggest that SP + CG flashes often are part of multi-CG flash processes. One case of a lightning process associated with a sprite consisted of 7 CG flashes.

Highlights

Sprites are electric discharges in the Mesosphere above thunderstorms
Two Mesoscale Convective Systems (MCS) in France each with 27 recorded sprite events have been analyzed in terms of cloud structure, precipitation, and lightning activity
Both MCSs were of similar size (120,000 km2), and they produced sprites during distinct periods, one for the storm of 21 July and two for that of 11 September

Summary

Introduction

Sprites are electric discharges in the Mesosphere above thunderstorms. They are so-called Transient Luminous Events (TLEs) which include the “blue jet” from thunderstorm cloud tops into the stratosphere and the “elve” at the base of the ionosphere. After the first observation of sprites (Franz et al, 1990), it was soon realised that the large majority are induced by positive cloud-to-ground (+CG) flashes (Boccippio et al, 1995; Lyons, 1996). Whereas the peak current in +CGs are not well correlated with sprite occurrences (Lyons et al, 2003) the charge moment change (CM) (defined as the product of the mean altitude of the charge reservoir in the cloud and the amount of charge lowered to ground by a CG flash) is a much better predictor, as first suggested by Wilson (1925). As initially observed over the Great U.S Plains (Lyons, 1994) and confirmed by later observations (Yair et al, 2004; Hayakawa et al, 2004; Pinto et al, 2004; Neubert et al, 2005) the storms which produce sprites are often mesoscale convective systems (MCSs). The characteristics of the two storms are compared and several quantitative aspects are derived and compared with similar studies reported in the literature

Observation system and data

Case of 21 July 2003

Analysis and discussion

Findings

Lightning activity and sprite production

Conclusion