Further Insight into the Nature of Ball-Lightning-Like Atmospheric Pressure Plasmoids

Known since antiquity, ball lightning is a natural, long-lived plasma-like phenomenon associated with thunderstorms and is not well understood due to its rarity and unpredictability. A recently discovered laboratory phenomenon with striking similarity to ball lightning is observed when a high-power spark is discharged from a cathode protruding from a grounded electrolyte solution. Whereas several investigations of these long-lived plasmas have been reported over the past decade, the underlying chemical and physical processes are still unknown. The present work attempts to gain further insight into this phenomenon by examining the effect of electrolyte pH on the plasmoid and observing the chemical and physical structure of the plasmoid using high-speed schlieren videography and FTIR absorption spectroscopy. The results indicate that the lifetime and size of the plasmoid slightly increase as the pH of isoohmic electrolyte solutions deviate from neutrality. The observed absorption spectra of the plasmoids exhibit absorption cross sections in the 620-700, 1500-1560, 2280-2390, and 3650-4000 cm-1 ranges, the last attributed to the presence of water clusters. Finally, schlieren images revealed a single, sharp density gradient at the boundary layer of the top and sides of the expanding ball-shaped plasmoid, and turbulent mixing below the ball.