Determination of the electric field intensity and space charge density versus height prior to triggered lightning

Abstract

[1] We infer the vertical profiles of space charge density and electric field intensity above ground by comparing modeling and measurements of the ground-level electric field changes caused by elevating grounded lightning-triggering wires. The ground-level electric fields at distances of 60 m and 350 m were measured during six wire launches that resulted in triggered lightning. The wires were launched when ground-level electric fields ranged from 3.2 to 7.6 kV m−1 and the triggering heights ranged from 123 to 304 m. From wire launch time to lightning initiation time, the ground-level electric field reduction at 60 m ranged from 2.2 to 3.4 kV m−1, with little ground-level electric field reduction being observed at 350 m. We observed that the triggering heights were inversely proportional to the ground-level electric field when the wires were launched. Our Poisson equation solver simulates the ground-level electric field changes as the grounded wires extend in assumed vertically varying profiles of space charge density and electric field intensity. Our model reproduces the measured ground-level electric field changes when the assumed space charge density decays exponentially with altitude, with ground-level charge densities between 1.5 and 7 nC m−3, space charge exponential decay height constants ranging from 67 to 200 m, and uniform electric field intensities far above the space charge layer ranging from 20 to 60 kV m−1. Our model predicts typical charge densities on the wires of some tens of μC m−1 with milliampere-range currents flowing into the wires from ground to supply the wire charge.