The plasma sphere and its possible role in ball lightning

Summary form only given. Experimental studies with plasma spheres are incomplete thus far with respect to formation and diagnostics of stable luminous structures despite numerous investigations of electric gas discharges and hot metals. The subject of spherical plasma structure enters into the question of ball lightning, the mobile fireball observed in the atmosphere often associated with the appearance of ordinary lightning. A few experimental fireballs possibly resembling ball lightning have been reported from laboratory studies. In addition to plasma spheres, certain combustion fireballs have been noted, heated metal globes, and some electric discharges, especially luminous microwave discharges. In addition to other discrepancies the experimental observations of those generally taken to be plasma globes have not yet shown the mobility and flight over moderate distance observed with the natural phenomenon. The virial theorem imposes a severe restriction on the energy content of a plasma sphere in the atmosphere far smaller than some estimates of the energy displayed in a few occurrences of natural ball lightning.