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Abstract

Energy transfer between the magnetosphere and ionosphere is commonly discussed in terms of the ionospheric conductance, and quantitative estimates are used to set the inner boundary condition for MHD models. Using the usual electrostatic calculation and assuming an ionosphere that is sufficiently uniform in the horizontal direction, it is found that the ionospheric conductance does not depend on the transverse-spatial-scale until below about 10km. So it might come as a surprise that even in this simple geometry, an electromagnetic calculation of the ionospheric conductance finds strong scale size dependence up to a couple of hundred kilometers, culminating in a greatly reduced large-scale conductance. In this talk I will describe my recent electromagnetic calculation, and how such significant electromagnetic effects come to be. I will discuss wave-like effects and multi-modal effects and scattering effects, which all operate to determine the ionospheric conductance even when the ionosphere is horizontally uniform. The discussion will revolve around a simple gedanken experiment.