Extended Data Table 1 Lightning strike events during the campaign, and available diagnostics for each event
From: Laser-guided lightning
- Sixteen flashes were recorded by the current measuring system at the Säntis Tower during the experimental campaign from 21 July to 30 September 2021. Due to both the harsh experimental conditions as well as intrinsic instrument limitations (optical visibility, buffer size and electromagnetic perturbations), each event could not be recorded by all instruments. The status of the laser system and each measuring system, including a high-speed camera (HSC), an interferometer (INT), X-rays sensors (X-ray), an electric field 20 m from the tower (E-field (20 m)) and an electric field 15 km from the tower (E-field), for each of these events is given in Table 1. Five out of the 16 flashes were positive (POS), whereas eleven were negatives (NEG). Only three were recorded by at least one high-speed camera (two without laser and one with the laser on), whereas all but one were recorded by the interferometer. All investigated lightning strikes were of the upward type, like 97% of the strikes observed at Säntis since 201036. All four recorded laser events were positive; by contrast, 85% negative flashes, 12% positive flashes and 3% bipolar flashes were recorded during the summer of 2021. Assuming conditions during the campaign similar to the average of the ten previous years, the excess of positive flashes when the laser is on is significant beyond 10−3 (P-value = 6.7 × 10−6 obtained with unilateral χ2 test).
