Study of multiple ELVES at the Pierre Auger Observatory

ELVES are transient ring-shaped emissions occurring in the ionosphere above thunderstorms. Multi-ELVES are events consisting of two and up to four rings of light separated temporally by tens of microseconds. The Fluorescence Detector (FD) at the Pierre Auger Observatory has been detecting ELVES with a dedicated trigger since 2013. The high temporal resolution of 100 ns of the FD allows us to record the phototraces of the events in great detail. From the improved processing of the phototraces, we have observed ELVES with double and triple peaks. In fact, during the period 2014-20, about 27% of the events detected at Auger are multi-ELVES. The origin of multi-ELVES is still not fully understood, therefore in this work, we tested two models: the first one relates the temporal difference between two peaks (ΔT) to the rise (t_r) and fall (t_f) times of the current density pulse of the source beam; the second one relates the height of the intra-cloud lightning source (h_b) to ΔT and is used to study events with three or more peaks. From the first model, we can obtain combinations of t_r and t_f where ΔT tends to zero, i.e. the origin of the simple ELVES can also be explained. For this analysis, we compare the ELVES parameters measured in Auger with the lightning properties detected by Earth Networks, i.e. the location, waveform, and height of these sources.