Shreeharsh Mallick

The characteristics of negative cloud-to-ground (CG) lightning are studied by analyzing their electric field records acquired at the Lightning Observatory in Gainesville (LOG), Florida, in the summer of 2013. For 220 flashes containing 1000 strokes, flash multiplicity, interstroke interval, and first to subsequent return stroke field peak ratio are examined. On average, each flash has 4.5 strokes. The arithmetic and geometric means of interstroke interval are 80 ms and 53 ms, respectively. First to subsequent return stroke (RS) field peak ratio is on average 2.16. Normalized electric field peak of subsequent return stroke does not depend on stroke order. We also examined how the percentage of flashes with detectable preliminary breakdown (PB) pulse trains is effected by the signal/noise ratio, type of storm, distance from LOG, and peak current. Characteristics of preliminary breakdown pulse trains including pulse train duration, PB-RS time interval and PB/RS field peak ratio are analyzed.

We examine electric field waveforms produced by 69 negative return strokes in 13 flashes triggered using the rocket-and-wire technique at Camp Blanding, Florida, in 2012. The waveforms were recorded at the Lightning Observatory in Gainesville, at a distance of 45 km from the lightning channel. This is the first detailed characterization of far (essentially radiation) electric field waveforms produced by rocket-triggered lightning. The results will be used in examining similarities and dissimilarities between natural and rocket-triggered lightning processes.

An unusual natural lightning flash containing two negative strokes to ground was recorded at the Lightning Observatory in Gainesville (LOG), Florida, on June 8, 2013. The flash was apparently a bolt-from-the-blue, whose first-stroke leader emerged from the side of the cloud at a height of about 3.5 km above ground level. The first leader showed profuse branching and what appears to be corona-like formations with spatial extent of 100 to 200 m (probably an intensified portion of radial corona sheath) at the upper part of the channel. Leader branching process facilitated by two simultaneous space stems was observed. The corresponding step lengths were estimated to be 14 and 15 m. The first-stroke attachment process involved a streamer zone about 50 m in length. Second-stroke leader was also branched. One of the second-leader branches appeared to abruptly change its direction at the beginning of return stroke process.

We estimated the performance characteristics of the Global Lightning Dataset (GLD360) using rocket‐and‐wire triggered lightning data acquired at Camp Blanding, Florida, in 2011–2013. The data set consisted of 201 return strokes and 84 kiloampere‐scale (≥1 kA) superimposed pulses (initial continuous current pulses and M components) in 43 flashes. All the events transported negative charge to ground. The GLD360 detected 75 strokes and 4 superimposed pulses in 29 flashes. The resultant detection efficiencies were 67% for flashes, 37% for strokes, and 4.8% for superimposed pulses. Out of 75 detected strokes, one (1.3%) was reported with incorrect polarity. The median location error was 2.0 km, and the median absolute current estimation error was 27%. This is the first comprehensive evaluation of GLD360 performance characteristics relative to absolute ground truth, with all previous evaluations being at least in part relative to other locating systems. The results presented in this work may be applicable to regions in and around Florida.

Using a high‐speed optical imaging system specifically designed for observing the lightning attachment process, we have documented the process for stepped, dart, and dart‐stepped leaders in an anomalous rocket‐triggered lightning flash that terminated on a 10 m grounded utility pole. The initiation of the first return stroke was found to occur at a height of 23 ± 3 m above the top of the utility pole and was associated with three “slow front” dE/dt pulses. A time of 1.5 µs later, a fast rise in luminosity at 18 ± 2 m was associated with a “fast transition” dE/dt pulse. The first return stroke propagated bidirectionally from its initiation height, as did subsequent return strokes from their initiation heights of 8 ± 1 m to 16 ± 2 m above the top of the utility pole. The initial upward speed of the first return stroke was 1.4 × 10⁸ m/s, while its initial downward speed was 2.2 × 10⁷ m/s. The channel bottom luminosity of the first return stroke rose more slowly to a two or more times larger amplitude than that of the subsequent stroke luminosities. In contrast, the National Lightning Detection Network‐derived first‐return‐stroke peak current is smaller than that of the second and the third strokes, and our electric field records at 45 km show similar behavior for the initial field peaks of the first and subsequent strokes.

We have estimated the ENTLN (formerly WTLN) performance characteristics using data for 245 negative return strokes in 55 flashes triggered from June of 2009 to August of 2012 at Camp Blanding, Florida. Performance characteristics are presented for both originally reported lightning data and reprocessed lightning data (the new processor was introduced in November of 2012). After the reprocessing, the ENTLN performance characteristics changed (relative to those corresponding to the originally reported data) as follows. Flash detection efficiency increased from 80% to 89%, stroke detection efficiency increased from 49% to 67% percentage of misclassified events decreased from 60% to 52% median location error increased from 621 m to 687 m, and median absolute current estimation error decreased from 51% to 17%.