Measurement and analysis of ground‐level electric fields and wire‐base current during the rocket‐and‐wire lightning triggering process

Abstract

[1] We present ground-level electric field intensity and trigger-wire-base current measurements in Florida during 33 successful rocket-and-wire triggered lightning attempts, those which initiated a sustained upward leader, and 20 unsuccessful attempts. The electric field changes during wire ascent were measured at eight stations between 35 m and 208 m from the launch site while the electric fields produced by precursor discharges at the ascending wire tip were measured at 120 m and 220 m. Both relatively steady trigger wire currents in the milliampere-range and fast precursor currents in the ampere to hundred-ampere range were measured at the wire base. A total of 2196 individual precursors were measured in 45 launches with negative charge overhead, with 0 to 225 precursors per launch and each precursor depositing 1 μC to 157 μC of charge at the wire tip. With negative charge overhead, slowly varying currents measured during the wire ascent increased to a maximum value between 3 mA and 10 mA. Positive line charge densities on the trigger wire were inferred from both the wire-base current and the ground-level electric field reduction during wire ascent for 38 launches, ranging from 1 μC m À1 near ground to about 100 μC m À1 at 200 m to 300 m aloft. A comparison of successful launches and unsuccessful launches with negative charge overhead shows that successful launches tend to have larger trigger wire line charge densities and larger precursor charge magnitudes, implying larger electric fields aloft. Three unsuccessful triggering attempts were made with positive charge overhead.

Does the lightning current go to zero between ground strokes? Is there a current “cutoff”?

“…The accuracy of the XL measurement is also demonstrated by Ngin et al . [] who present XL measurement data in 2012 during the ascent of the trigger wire and find good agreement both with previously reported current measurements and with their simultaneous electric field measurements.…”

Observations of the initial stage of a rocket‐and‐wire‐triggered lightning discharge

“…The pulses are called precursors and correspond to attempted breakdown events as the wire ascends. In the process, they transfer up to a hundred microcoulombs or more of charge to ground [Ngin et al, 2013]. The precursor pulses (PCPs) occur both as isolated events, separated by tens of milliseconds, and in groups ("bursts") of pulses, separated by tens of microseconds [e.g., Biagi et al, 2009].…”

Lightning attachment processes of an “anomalous” triggered lightning discharge

“…The lightning flash contained nine negative return strokes, as determined from on‐site ICLRT electric field and electric field derivative measurements, descriptions of which are found in Jerauld [] and Ngin et al . []. LAPOS recorded only the first seven return strokes due to its limited recording length.…”