Los Alamos National Laboratory

FORTE Compact Intra-cloud Discharge Detection Parameterized by Peak Current


M J Heavner, D. M. Suszcynsky, A. R. Jacobson, B. D. Heavner, and D A Smith

LAUR-02-5759


Abstract


The ground-based Los Alamos Sferic Array (LASA) has recorded over 7 million lightning-related fast electric field change records since May 1998. The waveforms are characterized with estimated peak currents and event type. During April 1 - Aug. 31, 2001 and 2002, LASA was operated in support of GPS VHF observations of lightning. The majority of GPS/LASA coincident events were compact intracloud discharges, with a threshold in LASA estimated peak current required for GPS VHF detection. In order to understand the physical properties of these LASA events, we have compared FORTE VHF observations with LASA VLF observations of NBEs.

Motivation


A VHF receiver onboard a GPS satellite is observing lightning emissions. The present observations are being used to develop a GPS-constellation based global-lightning monitoring program called V-GLASS. The Los Alamos Sferic Array is providing ground-truth to the GPS observations. The routine event identification by LASA processing software identifies the dominance ~60% of positive narrow bipolar events (+NB) in the GPS/LASA coincident data set, as shown in the event type histogram below. In order to understand the +NB observations from GPS, we focus on understanding VHF FORTE observations of positive narrow bipolar events.

GPS/EDOT Event Type
     Histogram

Energetic intracloud events have previously been referred to as compact intracloud discharges (CIDs), energetic bipolars, and bipolar events. Their emissions have also been referred to with multiple terms, generally based on the specific signature in the data set, rather than any physical process or mechanism. The field change waveforms have been described as narrow positive and narrow negative bipolar pulses (+/- NB). Energetic intracloud VHF emissions, when recorded from space along with a ground reflection, were dubbed transionospheric pulse pairs (TIPPs).

Terminology notwithstanding, energetic ICs are distinguished from other lightning events by several noteworthy characteristics, including the following: 1. The discharges are among the most powerful source of lightning radiation in the HF/VHF radio bands 2. Energetic ICs are typically isolated in time from other detectable discharges on a time scale of at least a few milliseconds, but often represent the initial event in an otherwise `normal' intracloud lightning flash 3. Energetic ICs occur in both positive and negative polarities.


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