On the relationship between lightning superbolts and TLEs in Northern Europe

Abstract

Lightning occurrence at higher latitudes in northwestern Europe is by far less frequent than mainland continental and the Mediterranean during most of the year. Yet, as recent studies suggest, this region harbors a large fraction of the most energetic lightning flashes on Earth, commonly referred to as superbolts. In this study, we examine the time/locations of intense cloud-to-ground (CG) strokes (>200 kA in absolute value), provided by Météorage for the 10.5-year period (from Jan 2010 to Jul 2020), to present a high-resolution map of their distribution, pointing out relevant discrepancies observed between -CG and + CG, respectively. We additionally investigate the potential of superbolts to result in short-lived optical phenomena above thunderstorms, collectively known as transient luminous events (TLEs). Observations in the region indicate that isolated superbolts with substantial charge moment change can produce sprites during low active marginal winter thunderstorms, in the absence of concurrent IC/CG activity several minutes before and after the event. An example is described when 3 sprites were captured in a similar context during the night of 7th/8th February 2016. We suggest that: i) convergence and aerosols advection from sea surface and busy shipping lanes may favour deep convection and cloud electrification on the English Channel with respect to surrounding areas. Inherent differences in cloud charge structure of sea based storms could lead to faster negative leader vertical velocity than those for storms over land, on average, and hence in larger peak currents, determining the winter peak of negative superbolts in the area; ii) areas occupied by the most populated superbolt clusters can be used to conduct future research in the region, aimed at better characterising microphysical properties of superbolts and their potential in generating TLEs.