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. Deployed on the mountainous island of Corsica for thunderstormmonitoring purposes in the Mediterranean Basin, SAETTA is a network of 12 LMA(Lightning Mapping Array, designed by New Mexico Tech, USA) stations thatallows the 3-D mapping of very high-frequency (VHF) radiation emitted by cloud discharges in the60–66 MHz band. It works at high temporal ( ∼40  ns in each 80  µ s time window) and spatial (tens of meters at best) resolutionwithin a range of about 350 km. Originally deployed in May 2014, SAETTA wascommissioned during the summer and autumn seasons and has now been permanentlyoperational since April 2016 until at least the end of 2020. We firstevaluate the performances of SAETTA through the radial, azimuthal, andaltitude errors of VHF source localization with the theoretical model ofThomas et al. (2004). We also compute on a 240 km  ×  240 km domainthe minimum altitude at which a VHF source can be detected by at least sixstations by taking into account the masking effect of the relief. We thenreport the 3-year observations on the same domain in terms of number oflightning days per square kilometer (i.e., total number of days during whichlightning has been detected in a given 1 km square pixel) and in terms oflightning days integrated across the domain. The lightning activity is firstmaximum in June because of daytime convection driven by solar energy input,but concentrates on a specific hot spot in July just above the intersectionof the three main valleys. This hot spot is probably due to the low-levelconvergence of moist air fluxes from sea breezes channeled by the threevalleys. Lightning activity increases again in September due to numeroussmall thunderstorms above the sea and to some high-precipitation events.Finally we report lightning observations of unusual high-altitude dischargesassociated with the mesoscale convective system of 8 June 2015. Most ofthem are small discharges on top of an intense convective core duringconvective surges. They are considered in the flash classification of Thomaset al. (2003) to be small–isolated and short–isolated flashes. The other high-altitude discharges, much less numerous, are long-range flashes that developthrough the stratiform region and suddenly undergo upward propagationstowards an uppermost thin layer of charge. This latter observation isapparently consistent with the recent conceptual model of Dye and Bansemer (2019) that explains such an upper-level layer of charge in the stratiformregion by the development of a non-riming ice collisional charging in amesoscale updraft.

atmospheric measurement techniques

SAETTA: high-resolution 3-D mapping of the total lightning activity in the Mediterranean Basin over Corsica, with a focus on a mesoscale convective system event