“…Preliminary observations of early VLF events exhibited high variability in onset duration [ Inan et al , , ], defined as the time between the start of the event and the occurrence of the maximal amplitude/phase perturbation, ranging from ≤20 ms to ∼2 s. Since then, early event onset durations have been categorized as “fast” (onset duration ≤20 ms) [ Inan et al , ] and “slow” (between ∼0.5 and ∼2.5 s) [ Haldoupis et al , , ]. However, some studies after the work of Inan et al [] have utilized the term fast to describe events with slower onset durations of <50, <100, or 1000 ms [ Sampath et al , ; Kumar et al , ; Salut et al , ; Marshall et al , ]. We note that elves, sprite halos, and sprites have been observed with optical durations less than 20 ms [e.g., Stenbaek‐Nielsen et al , ; Stenbaek‐Nielsen and McHarg , ; Newsome and Inan , ].…”