Leader Studies with the Los Alamos Sferic Array
LAUR-01-4198
Abstract
The Los Alamos Sferic Array records the transient electrical
activity associated with lightning discharges between 1 - 500 kHz.
The multi-station array has been operated since 1998, routinely
geolocating lightning based on the differential times of arrival at
the stations. The fast electric field change records are
predominantly 8 ms record lengths but are occasionally collected with
longer record lengths (up to 1 s) to provide overall lightning
discharge context (including leader activity). The stations are
operated in a threshold-triggered mode and predominantly trigger on
initial return stroke activity. However, individual stations may
include leader radiation in the record or may even trigger on leader
activity. The large number (> 2,000,000) of lightning events
recorded provide a database for statistically significant studies of
leader waveform parameters. We present initial results of studies of
the leader activity in the sferic array database.
For a small number of leader events, the
FORTE satellite
recorded VHF emissions from individual leaders steps. The FORTE
observations allowed source altitude determination for multiple steps
and therefore vertical propagation velocity determination. One type
of leader provides large amplitude signatures in both the LF/VLF of
the sferic array and the VHF of FORTE. For this class of event, a
velocity of 10 6 m/s has been determined. This speed is
approximately an order of magnitude greater velocity than the typical
stepped-leader associated with an intial return stroke.
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