A physical model of lightning initiation on aircraft in thunderstorms

A physical model of initiation of lightning flashes by aircraft in thunderstorms, based on the “bi‐directional, uncharged leader” concept of Kasemir, is verified with airborne data from lightning strikes to instrumented airplanes (NASA F‐106B and FAA CV‐580). Characteristics of electromagnetic processes during lightning attachment to aircraft are identified with those in negative stepped leaders and positive leaders in natural lightning, in flashes triggered by wire‐trailing rockets, and in laboratory discharges. It is shown that (1) a triggered flash starts on aircraft with either a negative corona or a positive leader that depends on the ambient electric field vector and the vehicle form factors; (2) the positive leader with continuous current that increases with time to the level of several hundred amperes is followed in a few milliseconds by the negative stepped leader with current pulses of a few kiloamperes; and (3) the two leaders develop in space simultaneously and bi‐directionally from the oppositely charged extremities of the airplane.