The Theory of the Beta-Plane Baroclinic Topographic Modons

Form-preserving, uniformly translating, horizontally localized solutions (modons) are considered within the framework of nondissipative quasi-geostrophic dynamics for a two-layer model with meridionally sloping bottom. A general classification of the beta-plane baroclinic topographic modons ( g -BTMs) is given, and three distinct domains are shown to exist in the plane of the parameters. The first domain corresponds to the regular modons with the translation speed outside the range of the phase speeds of linear waves. In the second domain, modons cannot exist: only non-localized solutions are permissible here. The third domain contains both linear periodic waves and the so-called anomalous modons traveling without resonant radiation. Exact modon solutions with piecewise linear relation between the potential vorticity and streamfunction are found and analyzed. Special attention is given to the smooth regular dipole-plus-rider solutions (anomalous modons cannot carry a smooth axisymmetric rider). As distinct from their flat-bottom analogs, g -BTMs may have nonzero total angular momentum. This feature combined with the ability of g -BTMs to bear smooth riders of arbitrary amplitude provides the existence of almost monopolar (in both layers) stationary vortices.     

On the geo-electromagnetic aspects of tornado initiation

Summary 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.