On the geo-electromagnetic aspects of tornado initiation

Abstract

The reasoning that joule heating in multiple-stroke lightning flashes associated with an active tornado constitutes the major energy source for itsdrive is questioned. An electrical discharge is proposed as a mechanism for the formation of the initial vortexsink, a high specific-energy source being supplied by Joule heating in a leader-stroke coronal discharge of several hundred amperes and milliseconds duration. Magnetic pinch effects are invoked as a means of preventing large lateral heat losses from the ionised column and a resulting degradation of the energy source. Applying the equation for magneto-hydrostatic balance, it is shown that magnetic pinch exerted on the column by the current-induced magnetic field alone is insufficient to achieve balance and thus prevent energy losses. Qualitative arguments are used to demonstrate that the pinch effect can be enhanced through the interaction with the external, geomagnetic field. Observational evidence is presented to support the hypothesis of geomagnetic control for tornado initiation on a global scale. It is seen in large differences of tornado frequency between regions on the surface of the Earth featured by comparable pre-requisite thunderstorm frequency but significant differences in geomagnetic intensity which qualitatively agree with the predicted effect.