Ball Lightning

Prof. Kirthi Tennakone

Institute of Fundamental Studies, Sri Lanka

Tuesday - June 12, 2007

3:30pm - 4:30 pm

218 - Natural Science Center

Abstract:

The fascinating phenomenon of ball lightning (BL) continues to resist complete theoretical explanation and reproducible laboratory demonstration to cover all its manifestations. BL originates in the regions of electrical activity in the atmosphere as glowing balls drifting in air at near neutral buoyancy. It bounces away from surfaces and sometimes emits sparks on encounter with an obstacle. BL is formed near the ground and sometimes fall from clouds. There is evidence that balls carry charge and the electric field felt tens of meters away from the object. The ball lasts for several seconds and vanishes either explosively or silently. Most intriguing are the reports which indicate that BL passes through minute cracks and holes and restructure to its original spherical form. A model of ball lightning which accounts for most its properties will be presented.

Ball lightning is pictured as a negatively charged spherical bubble with a shell of oriented dipolar water molecules. The bubble is balanced by outward electrostatic stress and inward forces of atmospheric pressure and/or surface tension forces. Because of the very low electronic conductivity of condensed water, electrons slowly leak away from the surface in the radial direction forming a corona. The charge on the ball decays exponentially with a characteristic mean life time depending on the electronic conductivity of the shell. Protons confined in the shell induce an electric conductivity to the shell in the tangential direction. When the bubble is deformed by an inductive field, the mobility of protons develops a higher charge density in the more curved regions of the shell. Differential electrostatic stress generates a feedback propelling force enabling it to bounce off from surfaces or penetrate through holes. Model suggests that ground BL is associated with relatively rare positive lightning and also explains how BL could drop from clouds.