A mathematical model for a short gap breakdown in air was employed to exami
ne the nature of the initiating discharge on the dielectric surface of a di
electric/metallic electrode gap of 0.500 mm separation in a uniform electri
cal field at atmospheric pressure, The calculations demonstrate that in the
absence of field enhancing surface asperities, the incipient discharge, oc
curring on a dielectric surface, exhibits the pronounced breakdown channel
expansion characteristic of pulseless glow discharges.