Ball lightning as a free-force magnetic knot with linked streamers

Summary form only given. We consider a recently proposed model of ball lightning, based on the ideas of magnetic knot (a magnetic field with linked force lines) and free-force magnetic field (a magnetic field such that B/spl times/(/spl nabla//spl times/B)=0). The fireball is assumed to consist in an air ball coupled to a magnetic knot in such a way that the current flow along some streamers, separated from one another and also linked, so that the system is very tangled indeed. It turns out that the linking of the lines, which can be measured by the helicity integral (the integral of the scalar product A/spl middot/B), has a stabilizing effect on the system. The streamers are hot, in the range 16000 K-19000 K where the curve of the power density emitted by the plasma has a shoulder in which the emission is approximately constant, thus explaining why the ball loses energy by radiation without decreasing its radiance.