Early phase of lightning currents measured in a short tower associated with direct and nearby lightning strikes

Abstract

[1] Records of natural lightning currents of negative downward strokes measured at the base of a 60 m high instrumented tower are presented to denote patterns of their early phase. Such patterns in the records of five flashes and two upward unconnected leaders are discussed. Typical profiles of this early phase, comprising the pre-return-stroke pulses of the current flowing upwards the tower in response to the downward stepped leader approaching the ground, the concavity in the initial rising part of the return-stroke waveform, and the abrupt rise around the half-peak of the first-stroke waveform, are remarked. Statistics are developed for the pre-return-stroke pulses of current to characterize their amplitude, duration, interval, and risetime for both the first stroke and upward unconnected leaders, which proved to be quite similar. The ratio of the maximum pulse peak to first stroke peak is typically in the range 0.7% to 2.2% of the analyzed currents, different from the value of around 10% found for the distant electric fields radiated by first-stroke currents.Citation: Visacro, S., M. H. Murta Vale, G. Correa, and A. Teixeira (2010), Early phase of lightning currents measured in a short tower associated with direct and nearby lightning strikes,

High‐Speed Video and Lightning Mapping Array Observations of In‐Cloud Lightning Leaders and an M Component to Ground

“…LMA sources at the time of the second stroke and the ratio of the leader to return stroke field change indicate that the second stroke occurred in clear air below 1 km (see also, for reports of flashes in clear air; Krider, ; Waldteufel et al, ). Additionally, the final current pulse before the return stroke (bottom‐left panel of Figure ) does not have a coincident d E /d t pulse measured (typically due to stepping of the downward leader), suggesting that that current pulse is associated with stepping of the upward connecting leader (see also Biagi et al, , ; Guimaraes et al, ; Hill et al, ; Visacro et al, , ).…”

Updated statistics of lightning currents measured at Morro do Cachimbo Station

“…Optionally, this system can be set to register 0.5-s-long registers with a 17-ns resolution and 15-ms pre-trigger period. The new measuring system is able to record in detail the whole flash current, comprising the full impulsive waves of first-and of subsequent-stroke currents, the initial rising part of the return-stroke waveforms and the early phase corresponding to the pre-return-stroke pulses of current induced along the tower in response to the step leader approaching the ground (Visacro et al, 2010). Fig.…”

Assessing events of upward lightning measured at Morro do Cachimbo Station

“…The current transducers feed an eight-channel data acquisition board with a sampling rate of 60 MS/s [1][2]. The electric-field measuring system, consisting of Whip antennas installed in a horizontal position 45 m away from the tower [3] detects the variation of such field associated to nearby strokes (up to 10 km distant).…”