Abstract

Local differences of the horizontal components of transient geomagnetic variations have been recorded by using sensitive variometers associated with a telemetric link. Instead of studying a relation between the variations of the vertical anomalous components and horizontal normal ones, we have studied in the time domain, the spatial distribution of the quantities: Delta H oi (t) = H i (t) - H o (t) and Delta D oi (t) = D i (t) - D o (t), which represent the differences between the horizontal components of the transient field at station i and at station o chosen as the reference station.These differences can be interpreted, in every station, as the components of a horizontal anomalous field which has interesting properties: It has a purely internal origin. Its direction in space remains constant. In its expression, time and space variables are naturally separated.The devices that we use allow us to determine the modulus and the direction of the anomalous field in real time without any scattering. The properties of the anomalous field are found to be incompatible with the hypothesis of a local induction in a conductive structure, but can easily be explained by a current concentration in a conductive structure.

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