Jeff Lapierre

On the relationship between continuing current and positive leader growth

It has long been speculated that the source of continuing current (CC) for a negative cloud-to-ground flash is provided by the growth of its positive leader into negative charge regions. In this study, data from the Langmuir Electric Field Array (LEFA) and Lightning Mapping Array (LMA) are used to investigate these speculations. LEFA and LMA data provide a way to estimate the occurrence and duration of CC and channel growth throughout a flash, respectively. By connecting LMA VHF sources onto contiguous channels, the growth of the positive leader associated with each return stroke is inferred. A linear correlation between positive-channel growth and CC duration is found, providing evidence that the positive leader grows with a constant velocity, but no obvious correlation of this velocity with CC occurrence is found. Each return stroke is then sorted by its channel growth rate and further identified by its CC type. This analysis also provides no identifiable correlation linking the positive-channel growth rate to CC occurrence or duration. Finally, the positive-channel growth rate for the whole flash is calculated in 10 ms windows so that any trends occurring before, during, or after the CC can be observed. This analysis too shows no correlation, which implies that positive-channel growth is not the primary mechanism that determines CC occurrence and duration.

Location and analysis of acoustic infrasound pulses in lightning

Acoustic, VHF, and electrostatic measurements throw new light onto the origin and production mechanism of the thunder infrasound signature (<10 Hz) from lightning. This signature, composed of an initial compression followed by a rarefaction pulse, has been the subject of several unconfirmed theories and models. The observations of two intracloud flashes which each produced multiple infrasound pulses were analyzed for this work. Once the variation of the speed of sound with temperature is taken into account, both the compression and rarefaction portions of the infrasound pulses are found to originate very near lightning channels mapped by the Lightning Mapping Array. We found that none of the currently proposed models can explain infrasound generation by lightning, and thus propose an alternate theory: The infrasound compression pulse is produced by electrostatic interaction of the charge deposited on the channel and in the streamer zone of the lightning channel.

Estimating detection efficiency in the absence of satellites: ENTLN detection efficiency in 2015 and 2016

To estimate the detection efficiency of a ground based lightning location system, typically the ground based locations are compared to those seen by satellite. This works well because the detection efficiency of the satellite is relatively uniform with space, and reasonably good. However, this technique does not work for the 2015 or 2016 calendar years because the LIS satellite used is no longer in orbit, and has only recently been replaced by ISS-LIS. In this study, we will investigate applying a machine learning regression algorithm Lasso to lightning parameters determined by ENTLN to see if it is possible to estimate the detection efficiency of the network without satellite data.