Analysis of microsecond- and submicrosecond-scale electric field pulses produced by cloud and ground lightning discharges

doi:10.1016/j.atmosres.2008.01.014

Atmospheric Research

Volume 91, Issues 2–4, February 2009, Pages 316-325

https://doi.org/10.1016/j.atmosres.2008.01.014 Get rights and content

Abstract

We examined microsecond- and submicrosecond-scale pulses in electric field records of cloud and cloud-to-ground lightning discharges acquired in summer 2006, in Gainesville, Florida. A total of 12 cloud and 12 ground flashes were analyzed in detail, with the electric field record length being 96 or 200 ms and sampling interval being 4 or 10 ns. The majority of pulses in both cloud and ground discharges analyzed in this study were associated with the initial breakdown process and were relatively small in amplitude and duration. The typical durations were an order of magnitude smaller than tens of microseconds characteristic of “classical” preliminary breakdown pulses. We estimated that 26% of the pulses in the 12 cloud discharges and 22% of the pulses in the 12 cloud-to-ground discharges had total durations less that 1 µs.

Introduction

Cloud discharges can be viewed as being composed of an early or active stage and a late or final stage. The beginning of a cloud discharge is typically marked by the largest microsecond-scale pulses in its wideband electric field record that are presumably related to the flash initiating breakdown process. The typical total pulse duration of individual initial breakdown pulses is in the range of 50 to 80 µs with typical interpulse interval of 600 to 800 µs (Rakov et al., 1996). Microsecond-scale pulses in cloud discharges were analyzed by Villanueva et al. (1994), although pulses that were smaller than 12.5% of the average amplitude of the five largest pulses in a flash (in some flashes there were hundreds of them) were not included in the analysis. In the present study, we extend the work of Villanueva et al. (1994) to additionally include these smaller pulses by examining their total duration, amplitude, and occurrence. Additionally, our sampling interval of 10 ns (for cloud discharges) versus 500 ns in Villanueva et al.'s (1994) study allowed us to include submicrosecond-scale pulses in the analysis. Examined here are pulses occurring primarily during the early stage of cloud flashes. The final stage of cloud flashes generally could not be examined due to limited record length (200 ms for cloud discharges).

In cloud-to-ground discharges, a predominantly bipolar pulse train sometimes appears a few to several tens of milliseconds before the first return-stroke. This pulse train is commonly attributed to preliminary (initial) breakdown and hence referred to as the preliminary breakdown pulse train. The typical total pulse duration of individual pulses in the train is 20 to 40 µs with typical interpulse interval in the range of 70 to 130 µs (Rakov et al., 1996). In this paper, we examine only pulses occurring prior to the first return-stroke pulse, most of which were associated with the preliminary breakdown pulse train.

Section snippets

Instrumentation and methodology

The data used in this study were acquired during summer 2006 in Gainesville, Florida. A total of 12 cloud discharges and 12 negative cloud-to-ground discharges with a relatively large number of pulses within the length of the record (96 or 200 ms) were selected for analysis. Using thunder ranging and the characteristic features of return-stroke electric field waveforms at known distances in the 50 to 250 km range (Pavlick et al., 2002; Fig. 5), we estimated that the majority of our records are

Cloud discharges

The peak-to-peak amplitude of each bipolar pulse and zero-to-peak amplitude of each unipolar pulse in a particular cloud discharge was normalized with respect to that of the largest pulse in the flash. Pulses were grouped into four different categories depending upon the value of its normalized amplitude as shown in Table 1. The time at which the pulse having the largest peak-to-peak amplitude in a particular flash occurred was relabeled as the zero of the time scale (t = 0) and positions of all

Conclusions

The majority of pulses in the early stage of cloud discharges and those occurring prior to the first return stroke in cloud-to-ground discharges are typically small in both amplitude and duration. Amplitudes of these most common pulses are 50% or less than that of the largest pulse, and their durations are less than or equal to 4 µs. In contrast, total durations of “classical” initial breakdown pulses in both cloud and cloud-to-ground flashes are thought to be considerably longer, typically

Acknowledgment

This study was supported in part by NSF grant ATM-0346164.

References (5)

PavlickA. et al.
Characteristics of distant lightning electric fields
RakovV.A. et al.
Lightning: Physics and Effects
(2003)

There are more references available in the full text version of this article.

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Throughout this paper, the term used for the series of E-field bipolar pulses initiating all flashes is IB pulses. The IB pulses can be classified into 2 categories, namely classical and narrow pulses (Nag and Rakov, 2008 and Nag et al., 2009). The classical IB pulses have pulse durations of 10 μs and longer, while for narrow IB pulses the typical pulse durations are below 10 μs (microsecond and sub-microsecond scale pulses; refer to Fig. 7a and b in Nag et al., 2009).
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