Some Problems of Electromagnetic Induction in the Equatorial Electrojet Region--I Magneto-telluric Relations

Abstract

General theoretical expressions have been obtained for time variations of the magnetic and electric fields in the vicinity of the magnetic dip equator. From these, magneto-telluric ratios have been determined for a number of earth models, including the general case of n stratified layers, and these are found to be functions of the dimension of the inducing field as well as of the earth conductivity structure and the period of the variation. Model apparent resistivity curves have been computed for the same earth models as used by other research workers and the differences between them are discussed. Some of the problems which have to be considered in the practical application of the magneto-telluric expressions are noted and attention is drawn to the rapid change in the value of the apparent resistivity with electrojet width for variations of period greater than several hours.

Some Problems of Electromagnetic Induction in the Equatorial Electrojet Region--II The Analysis of Magnetic and Telluric Variations at Zaria, Nigeria

“…An outline of the preliminary theory, in which the Hy variation is assumed negligible, was published previously (Hutton 1969) and a more general discussion of the problem has now been completed (Hutton 1972). Only the main assumptions concerning the nature of the magnetic field variations near the dip equator and the resulting expressions required for the present discussion are given here.…”

Electrical conductivity of the Earth's mantle from the first Swarm magnetic field measurements

“…This is a simplification considering the complexity of separating ionospheric from magnetospheric parts. Nevertheless, we restrict ourselves to periods larger than 1 day to further reduce the effect of the ionospheric field at shorter periods [ Hutton , ]. For each day we select the residual measurements of the three satellites and estimate the external magnetospheric field and its induced counterpart.…”

A study of transient variations in the Earth's electromagnetic field at equatorial electrojet latitudes in western Africa (Mali and the Ivory Coast)

“…Surface magnetic data clearly shows that the equatorial electrojet ionospheric equivalent currents are symmetrical with respect to the center of the jet. Other symmetrical distributions of ionospheric equivalent currents have been used to solve the induction problem: For example, a cosine distribution with`half-period' a c : (Hutton, 1972) sx s 0 cos 2x 8b or a gaussian distribution scaled by a`standard deviation' a g (Peltier and Hermance, 1971)…”