The Los Alamos Sferic Array: A research tool for lightning investigations

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Abstract
Since 1998 the Los Alamos Sferic Array (LASA) has recorded electric field change signals from lightning in support of radio frequency (RF) and optical observations by the Fast On‐orbit Recording of Transient Events (FORTE) satellite. By “sferic” (a colloquial abbreviation for “atmospheric”), we refer to a remote measurement of the transient electric field produced by a lightning flash. LASA consisted of five stations in New Mexico in 1998 and was expanded to 11 stations in New Mexico, Texas, Florida, and Nebraska in 1999. During the 2 years of operation described in this paper, the remote stations acquired triggered 8‐ or 16‐ms duration, 12‐bit waveforms and GPS‐based sferic time tags 24 hours per day year‐round. Source locations were determined daily using differential time of arrival techniques, and the waveforms from all geolocated events were transferred to Los Alamos National Laboratory (LANL), where they have been archived for further analysis, including event classification and characterization. We evaluated LASA location accuracy by comparing temporally coincident (occurring within 100 μs) LASA and National Lightning Detection Network (NLDN) event locations. Approximately one half of the locations agreed to within 2 km, with better agreement for events that occurred within the confines of LASA subarrays in New Mexico and Florida. Of the ∼900,000 events located by the sferic array in 1998 and 1999, nearly 13,000 produced distinctive narrow bipolar field change pulses resembling those previously identified as intracloud discharges.