On the problem of simulating the Earth's induction effects in modeling polar magnetic substorms

Abstract

A major problem encountered in trying to model the current system associated with a polar magnetic substorm from ground‐based magnetic observations is the difficulty of adequately evaluating the earth's induction effects. Two methods for simulating these effects are reviewed here. Method 1 simply reduces the earth to a perfect conductor and leads to very simple field equations. Method 2 considers the earth as a ‘horizontally’ layered body of finite conductivity but requires a large amount of computational time. The performances of both methods are compared when the substorm current system can be approximated by an infinitely long electrojet flowing over a flat earth. In this case it appears that for most substorm modeling problems it is sufficient to treat the earth as a perfect conductor. The depth of this perfect conductor below the earth's surface should be selected in function of the source frequency content.