Early VLF perturbations caused by lightning EMP‐driven dissociative attachment

Abstract

We propose a new mechanism for lightning‐induced perturbations to VLF transmitter signals known as Early VLF events. This mechanism involves electron density changes due to electromagnetic pulses (EMP) from successive in‐cloud lightning discharges associated with cloud‐to‐ground discharges (CGs), which are likely the source of continuing current and much of the charge moment change in CGs. Through time‐domain modeling of the EMP we show that a sequence of pulses can produce appreciable density changes in the lower ionosphere, and that these changes are primarily electron losses through dissociative attachment to molecular oxygen. Modeling of the propagating VLF transmitter signal through the disturbed region shows that perturbed regions created by successive horizontal EMPs create measurable amplitude changes.