Library of Congress Cataloging in Publication Data Marchuk, G. I. (Gurii Ivanovich), 1925-Difference methods and their extrapolations.

42 2.3 Three-dimensional finite elements. .. .. 45 2.3.1 Elements with a tetrahedral cell. . 47 2.3.2 Elements with a mesh shaped as a rectangular parallelepiped. 49 2.4 Affine and isoparametric transformations. .. . .

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Abstract.A quantitative division of the ionosphere into dynamo and motor regions is performed on the base of empirical models of space distributions of ionospheric parameters. Pedersen and Hall conductivities are modified to represent an impact of acceleration of the medium because of Ampére's force. It is shown that the currents in the F 2 layer are greatly reduced for processes of a few hours duration. This reduction is in particular important for the night-side low-latitude ionosphere. The International Reference Ionosphere model is used to analyze the effect quantitatively. This model gives a second high conducting layer in the night-side low-latitude ionosphere that reduces the electric field and equatorial electrojets, but intensifies night-side currents during the shortterm events. These currents occupy regions which are much wider than those of equatorial electrojets.It is demonstrated that the parameter σ d =σ P +σ H H / P that involves the integral Pedersen and Hall conductances P , H ought to be used instead of the local Cowling conductivity σ C in calculations of the electric current density in the equatorial ionosphere. We may note that Gurevich et al. (1976) derived a parameter similar to σ d for more general conditions as those which we discuss in this paper; a more detailed description of this point is given in Sect. 6. Both, σ d and σ C , appear when a magnetic field line is near a nonconducting domain which means zero current through the boundary of this domain. The main difference between σ d and σ C is that σ d definition includes the possibility for the electric current to flow along a magnetic field line in order to close all currents which go to this line from neighboring ones. The local Cowling conductivity σ C corresponds to the current closure at each point of a magnetic field line. It is adequate only for a magnetic field line with constant local conductivity at the whole line when field-aligned currents do not exist because of symmetry, but σ C =σ d in this case. So, Correspondence to: H. K. Biernat (helfried.biernat@oeaw.ac.at) there is no reason to use the local Cowling conductivity while the Cowling conductance C = P + 2 H / P is a useful and well defined parameter.