On the Triggering Mechanisms of Upward Lightning

Abstract

Upward lightning studies took place in Rapid City, South Dakota, USA and S. Paulo, Brazil during the summer thunderstorm seasons from 2011 to 2016. One of the main objectives of these campaigns was to evaluate and characterize the triggering of upward positive leaders from tall objects due to preceding nearby flash activity. 110 upward flashes were observed with a combination of high- and standard-speed video and digital still cameras, electric field meters, fast electric-field antenna systems, and for two seasons, a Lightning Mapping Array. These data were analyzed, along with correlated lightning location system data, to determine the triggering flash type responsible for the initiation of upward leaders from towers. In this paper, we describe the various processes during flash activity that can trigger upward leaders from tall objects in the USA and in Brazil. We conclude that the most effective triggering component is the propagation of the in-cloud negative leader during the continuing current that follows a positive return stroke.

Optical observation of needles in upward lightning flashes

“…An upward flash starts when the intensification of the electric field over a tall structure initiates an upward propagating leader from the tip of the structure. As reported by past studies using high-speed cameras and electric-field antennas in the USA and in Brazil, the initiation of positive leaders is usually triggered by a nearby flash activity 13 , 15 , 16 . Once the upward leader starts its propagation toward the cloud base, it may or may not branch before reaching the cloud base.…”

On the Initiation of Upward Negative Lightning by Nearby Lightning Activity: An Analytical Approach

“…The rest of the paper is organized as follows. Section 2 presents a brief description of the triggering scenarios proposed by Schumann et al (2019). Section 3 presents simulations of the vertical electric field for each of these scenarios.…”

“…Discussion is given in Section 5 and conclusions in Section 6. Saba et al (2016) and Schumann et al (2019) observed different scenarios leading to the triggering of an upward flash from a tower. All of them are characterized by a horizontal leader propagation over the tower.…”

“…Schumann et al (2019) reported occurrence statistics from both hemispheres at two observations sites in Rapid City and in Sao Paulo. Relatively similar occurrence statistics have been observed at these two sites (see Table 2 of Schumann et al, 2019). The reported values in Figure 1 are average values taking in account sample sizes from these two sites.…”

Characteristics of Electric Currents in Upward Lightning Flashes From a Windmill and its Lightning Protection Tower in Japan, 2005–2016

“…Schumann et al. (2019) described various sceneries leading to the triggering of UL from tall structures in the USA and Brazil. Such sceneries are recently confirmed by the analytical research conducted by Sunjerga et al.…”