On the prediction of low‐frequency geomagnetic pulsations for geophysical prospecting

Abstract

Pulsations of the earth’s magnetic field due to solar‐terrestrial interaction are used for geomagnetic soundings to study conductive structures in the earth. However, the pulsations are also the unwanted background noise for magnetic exploration surveys. It is, therefore, desirable to conduct the sounding or survey work during geomagnetic conditions optimum for that particular undertaking. This paper relates the pulsational activity to a parameter (the DRX index) which characterizes the magnetic activity for each individual day and which is routinely forecast in Canada. By using the relations established in this study, it is possible to infer the future levels of pulsations from the forecast DRX, and a period of desired pulsational activity can thus be selected for the field work. In the course of a day, the afternoon is appropriate for conducting magnetic surveys because of a generally lower level of pulsational activity and a virtual absence of intense short‐period pulsations, while morning is optimal for carrying out induction soundings because of more intense pulsational activity and a tendency of enhanced long‐period pulsations to recur during that time of day.