No abstract

We present a new engineering model for the M component mode of charge transfer to ground that can predict the observed electric field signatures associated with this process at various distances, including (a) the microsecond‐scale pulse thought to be due to the junction of in‐cloud leaders and the grounded, current‐carrying channel and (b) the ensuing slow, millisecond‐scale pulse due to the M component proper occurring below the junction point. We examine the features of 13 microsecond‐scale, fast electric field pulses associated with M component processes in upward negative lightning initiated from the Säntis Tower and recorded 14.7 km from it. Eleven out of the 13 pulses were found to be unipolar with pulse widths in the range of 9.8 to 35 μs, and the other two were bipolar. To model the process that gives rise to microsecond‐scale pulses, we hypothesize that the current pulses propagating away from the junction point along the main lightning channel (below the junction point) and along the feeding in‐cloud leader channel (branch) carry the same amount of charge. We further assume that the pulse traversing the branch is similar to a subsequent return‐stroke (RS) pulse. In the model, the RS‐like process is represented by the MTLE model. The millisecond‐scale field signature that follows the initial fast pulse in M components at close distances is simulated in our model using the guided‐wave M component model. The proposed model successfully reproduces the vertical electric field waveforms associated with M‐component processes in upward lightning flashes initiated from the Säntis Tower at 14.7‐km distance from the lightning channel, in which both the fast, microsecond‐scale and the following slower, millisecond‐scale pulses were observed. The model also reasonably reproduces the known features of electric field signatures at close distances (up to 5 km), where the amplitude of the millisecond‐scale hook‐like pulse is much larger than that of the microsecond‐scale pulse, and at far distances (of the order of 100 km), where the microsecond‐scale pulses are dominant.

In the summer of 2013, a three-dimensional (3D)-based Foshan Total Lightning Location System (FTLLS), embedded with differential time of arrival (DTOA) techniques, was installed and started its operation in Foshan, Guangdong Province, China. In this paper, the geographical distribution and set-up information of FTLLS, the estimated locating errors and locating results, as well as its initial operation results are presented. FTLLS consists of nine sub-stations that receive electromagnetic waves associated with lightning discharges and locates VLF/LF (200 Hz–500 kHz) radiation sources in 3D. The remote sub-stations acquired triggered waveforms with a duration of 0.5 ms, a resolution of 12-bits, and a GPS-based sferic time tags of 24 h per day. Cloud-to-ground (CG) lightning events, intra-cloud (IC) lightning events and narrow bipolar events (NBEs) were located by FTLLS. Based on the Monte Carlo simulation, the two-dimensional horizontal location error is basically less than 100 m, and the vertical error (altitude) is less than 200 m when the lightning event occurs within the network. On the other hand, over 14 million lightning strikes were recorded successfully by FTLLS during the period of May to October in 2014, among which IC events, CG events and NBEs accounted for 65%, 34% and 1%, respectively. It is shown that FTLLS is capable of a fine three-dimensional (3D) location, in which the altitude parameters obtained are reasonable and well consistent with observed data in the previous studies. The location results of thunderstorms were additionally verified through simultaneously-observed radar data.