Detalied Study of Lightning Rod Emission from a Nearby Flash*

About 25 years ago, an extensive study on lightning rods was conducted at the Langmuir Laboratory for Atmospheric Research in New Mexico, USA. During this study, lightning rods with different shapes were exposed to high electric fields in a thunderstorm environment. The lightning rods were instrumented with current measurement systems that were able to measure small current bursts. Given the advances in lightning instrumentation since that time, we have begun to revisit these measurements complemented by a lightning mapping array, faster current measurements, and multiple fast/slow antennae. In the summer of 2024, we measured current emission from a nearby flash (characteristics of the flash) with two lightning rods. A "blunt" rod (with a diameter of 1.3 cm and a radius of roughly 6~mm) and a "sharp" rod (with the same diameter and a radius of < 1 mm) were placed atop South Baldy on 6~m masts.  An isolated sense wire connected each rod to the ground, while Pearson current transformers allowed measurements of current emissions. The sharp rod had a Pearson Model 110 (1809), bandwidth of 1 Hz to 20 MHz, and a calibration factor of 1 V = 10 A. Our blunt rod, however, had a Pearson Model 325, bandwidth of 160 Hz to 10 MHz, and a calibration factor of 1 V = 4 A. The chosen flash, which took place on July 7th, 2024, at 00:03:10.515432, is a classic negative cloud-to-ground lightning strike. Consistent with previous results, we observed that current pulses (in the tens of mA range) were associated with the leader approach and that they were terminated by a nearby return stroke. Also, the frequency of pulses increased as the leader approached the ground.